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Release 2.7.1, 2016-07-18
=========================
- Ported to Coq 8.5pl2.
Bug fixing:
- Fixed a compile-time assertion failure involving builtins
taking a 64-bit integer parameter and given an unsigned 32-bit integer
argument.
- Updates to the Cminor parser.
Release 2.7, 2016-06-29
=======================
Major improvement:
- The proof of semantic preservation now accounts for separate compilation
and linking, following the approach of Kang, Kim, Hur, Dreyer and
Vafeiadis, "Lightweight verification of separate compilation", POPL 2016.
Namely, the proof considers a set of C compilation units, separately
compiled to assembly then linked, and shows that the resulting
assembly program preserves the semantics of the C program that would
be obtained by syntactic linking of the source C compilation units.
Language features:
- Parse the _Noreturn function attribute from ISO C11.
- New standard includes files: <iso646.h> and <stdnoreturn.h> from ISO C11.
- New built-in functions: __builtin_clzl, __builtin_clzll
(count leading zeros, 32 and 64 bits) for ARM, IA32 and PowerPC;
__builtin_ctz, __builtin_ctzl, __builtin_ctzll
(count trailing zeros, 32 and 64 bits) for IA32.
Formal C semantics:
- The semantics of conversions from pointer types to _Bool
is fully defined (again).
Usability:
- The generation of DWARF debugging information in "-g" mode is now
supported for ARM and IA32 (in addition to PowerPC).
Coq development:
- Revised the Stacking pass and its proof to make it more extensible
later to e.g. 64-bit integer registers.
- Use register pairs in function calling conventions to control more
precisely the splitting of 64-bit integer arguments and results
into pairs of 32-bit quantities
- Revised the way register conventions are described in Machregs
and Conventions.
- Simulation diagrams now live in Prop instead of Type.
OCaml development:
- Code cleanup to remove warnings, support "safe strings" mode,
and be fully compatible with OCaml 4.02 and 4.03.
- Cminor parser: support for single-precision FP numbers and operators.
Bug fixing:
- Some declarations within C expressions were incorrectly ignored
(e.g. "sizeof(enum e {A})").
- ARM in Thumb mode: incorrect "movs" instructions involving the stack
pointer register were generated.
Bug fixing:
- Issue #179: clightgen produces wrong output for "switch" statements.
Release 2.6, 2015-12-21
=======================
Usability:
- Generation of full DWARF v2 debugging information in "-g" mode,
including function-local variables. This is fully supported
for the PowerPC target with GNU tools or Diab tools. Support
for IA32 and ARM is nearly there.
- Production of detailed explanations for syntax errors during parsing.
(Exploiting recent work by F. Pottier on the Menhir parser generator.)
- PowerPC port: added many new builtin functions.
Code generation and optimization:
- Support for PowerPC 64-bits (pointers are still 32-bit wide)
and Freescale's E5500 variant.
- More prudent alias analysis for operations over pointers that are
formally undefined, such as bit masking.
- New pass: Debugvar, to associate debug information to local variables.
Coq development:
- Richer representation of arguments and results to builtin operations.
- As a consequence, annotation builtins no longer need special handling.
- Added EF_debug builtins to transport debugging information throughout
the compiler back-end.
- Upgraded the Flocq library to version 2.5.0.
Bug fixing:
- Issue #71: incorrect initialization of an array of wchar_t
- Corrected the handling of bit-fields of type _Bool and width > 1
- Removed copy optimization when returning a struct from a function.
- Full parsing of unprototyped (K&R-style) function definitions.
(Before, the parsing was incomplete and would reject some definitions.)
Miscellaneous:
- The cchecklink tool (for a posteriori validation of assembly
and linking) was removed. It is replaced by the Valex tool,
available from AbsInt.
- Added a command-line option -conf <config file> to select
a different "compcert.ini" configuration file.
- Removed the command-line options -fstruct-passing=<convention>
and -fstruct-return=<convention>, more confusing than useful.
- Added a command-line option -fstruct-passing that activates
ABI-conformant by-value passing of structs and unions as
function arguments or results. If this option is not set,
passing a struct/union as function argument is now rejected.
- The -fstruct-return command-line option is deprecated and
becomes a synonymous for -fstruct-passing.
- The return type of __builtin_clz() is "int", as documented,
and not "unsigned int", as previously implemented.
Release 2.5, 2015-06-12
=======================
Language features:
- Extended inline assembly in the style of GCC. (See section 6.5
of the user's manual.) The implementation is not as complete
as that of GCC or Clang. In particular, the only constraints
supported over operands are "r" (register), "m" (memory), and
"i" (integer immediate).
Code generation and optimization:
- Revised translation of '||' and '&&' to Clight so as to
produce well-typed Clight code.
- More prudent value analysis of uninitialized declarations of
"const" global variables.
- Revised handling of "common" global declarations, fixes an issue
with uninitialized declarations of "const" global variables.
Improvements in confidence:
- Formalized the typing rules for CompCert C in Coq and verified
a type-checker, which is used to produce the type annotations
in CompCert C ASTs, rather than trusting the types produced by
the Elab pass.
- Coq proof of correctness for the Unusedglob pass (elimination
of unreferenced static global definitions). The Coq AST for
compilation units now records which globals are static.
- More careful semantics of comparisons between a non-null pointer
and the null pointer. The comparison is undefined if the non-null
pointer is out of bounds.
Usability:
- Generation of DWARF v2 debugging information in "-g" mode.
The information describes C types, global variables, functions,
but not yet function-local variables. This is currently available
only for the PowerPC/Diab target.
- Added command-line options to turn individual optimizations on or off,
and a "-O0" option to turn them all off.
- Revised handling of arguments to __builtin_annot so that no code
is generated for an argument that is a global variable or a local
variable whose address is taken.
- In string and character literals, treat illegal escape sequences
(e.g. "\%" or "\0") as an error instead of a warning.
- Warn if floating-point literals overflow or underflow when converted
to FP numbers.
- In "-g -S" mode, annotate the generated .s file with comments
containing the C source code.
- Recognize and accept more of GCC's alternate keywords, e.g. __signed,
__volatile__, etc.
- cchecklink: added option "-files-from" to read .sdump file names
from a file or from standard input.
ABI conformance:
- Improved ABI conformance for passing values of struct or union types
as function arguments or results. Full conformance is achieved on
IA32/ELF, IA32/MacOSX, PowerPC/EABI, PowerPC/Linux, and ARM/EABI.
- Support the "va_arg" macro from <stdarg.h> in the case of arguments
of struct or union types.
Coq development:
- In the CompCert C and Clight ASTs, struct and union types are now
represented by name instead of by structure. A separate environment
maps these names to struct/union definitions. This avoids
bad algorithmic complexity of operations over structural types.
- Introduce symbol environments (type Senv.t) as a restricted view on
global environments (type Genv.t).
- Upgraded the Flocq library to version 2.4.0.
Bug fixing:
- Issue #4: exponential behaviors with deeply-nested struct types.
- Issue #6: mismatch on the definition of wchar_t
- Issue #10: definition of composite type missing from the environment.
- Issue #13: improved handling of wide string literals
- Issue #15: variable-argument functions are not eligible for inlining.
- Issue #19: support empty "switch" statements
- Issue #20: ABI incompatibility wrt struct passing on IA32.
- Issue #28: missing type decay in __builtin_memcpy_aligned applied to arrays.
- Issue #42: emit error if "static" definition follows non-"static" declaration.
- Issue #44: OSX assembler does not recognize ".global" directive.
- Protect against redefinition of the __i64_xxx helper library functions.
- Revised handling of nonstandard attributes in C type compatibility check.
- Emit an error on "preprocessing numbers" that are invalid numerical literals.
- Added missing check for static redefinition following a non-static
declaration.
- Added missing check for redefinition of a typedef as an ordinary
identifier within the same scope.
Miscellaneous:
- When preprocessing with gcc or clang, use "-std=c99" mode to force
C99 conformance.
- Use a Makefile instead of ocamlbuild to compile the OCaml code.
Release 2.4, 2014-09-17
=======================
Language features:
- Support C99 compound literals (ISO C99 section 6.5.2.5).
- Support "switch" statements over an argument of type "long long".
Code generation and optimization:
- Revised and improved support for single-precision floating-point
arithmetic. Earlier, all FP arithmetic was performed at double
precision, with conversions to/from single precision as needed,
in particular when loading/storing a single-precision FP number
from/to memory. Now, FP operations whose arguments are of type
"float" are performed in single-precision, using the processor's
single FP instructions. Fewer conversions between double and
single precision are generated.
- Value analysis and constant propagation: more precise treatment of
comparisons against an integer constant.
Improvements in confidence:
- Full correctness proofs for the algorithms used in the runtime
support library for conversions between 64-bit integers and
floating-point numbers.
ARM port:
- Added support for Thumb2 instruction encoding (option -mthumb).
Thumb2 is supported on ARMv7 and up, and produces more compact
machine code.
- Exploit some VFPv3 instructions when available.
- Built-in function '__builtin_cntlz' (count leading zeros)
renamed '__builtin_clz' for GCC / Clang compatibility.
PowerPC port:
- Refactored the expansion of built-in functions and
pseudo-instructions so that it does not need to be re-done in
cchecklink.
- Updated the cchecklink validator accordingly.
- More efficient code generated for volatile accesses to small data areas.
- Built-in function '__builtin_cntlz' (count leading zeros)
renamed '__builtin_clz' for GCC / Clang compatibility.
IA32 port:
- Added built-in functions __builtin_clz and __builtin_ctz
(count leading / trailing zeros).
Coq development:
- The memory model was extended with two new "chunks", Many32 and Many64,
that enable storing any 32-bit value or 64-bit value using
an abstract, not bit-based encoding, and reloading these values exactly.
These new chunks are used to implement saving and restoring callee-save
registers that can contain data of unknown types (e.g. float32 or float64)
but known sizes.
- Refactored the library of FP arithmetic (lib/Floats.v) to support
both 64- and 32-bit floats.
Release 2.3pl2, 2014-05-15
==========================
Usability:
- Re-added support for "__func__" identifier as per ISO C99.
- Re-added some popular GCC extensions to ISO C99:
. alternate keywords __restrict, __inline__, etc,
. support for empty structs and unions
. support '\e' escape in char and string literals, meaning ESC
- Do not assume that the preprocessor removed all comments.
Bug fixing:
- Fixed regression on initializers of the form T x[N] = "literal";
where T is a typedef for a character type.
- "asm" statements were causing syntax errors.
- Better handling of "extern" and "extern inline" function definitions.
- Internal error on some octal escape sequences in string literals.
- Parsing of "#pragma section" directives made more robust and
with better error reporting.
Release 2.3, 2014-05-05
=======================
Language features:
- Support for C99 designated initializers. (ISO C99 section 6.7.8.)
Improvements in confidence:
- The parser is now formally verified against the ISO C99 grammar plus
CompCert's extensions. The verification proves that the parser
recognizes exactly the language specified by the grammar, and that
the grammar has no ambiguities. For more details, see the paper
"Validating LR(1) parsers" by Jacques-Henri Jourdan, François Pottier,
and Xavier Leroy, ESOP 2012, http://dx.doi.org/10.1007/978-3-642-28869-2_20
- More theorems proved about float<->integer conversions.
Optimizations:
- Optimize "x != 0", "x == 0", "x != 1", and "x == 1" when x is known
to be a boolean already, ranging over {0, 1, undef}.
- More systematic constant propagation in pass Selection, lightens
the work of later RTL optimisations.
- IA32: recognize and use the "not" instruction.
Usability:
- Option "-timings" to print compilation times for various passes.
- Various tweaks in IRC graph coloring to reduce compilation time.
- IA32: add built-in functions for fused multiply-add
(require a recent processor with FMA3 extensions).
Improvements in ABI conformance:
- New target platform: ARM with EABI "hard float" calling conventions
(armhf in Debian's classification).
- IA32 and ARM: revised handling of "common" variables to conform with ABI.
Bug fixing:
- In -fbitfields emulation: "a->f" was not properly rewritten if "a"
had "array of structs" type instead of "pointer to struct".
- Moved analysis of single-precision floats from RTLtyping to Machtyping.
(RTLtyping was incorrectly rejecting some functions involving
single-precision floats.) Simplified LTL semantics and Allocation
pass accordingly.
- Assignment to a l-value of "volatile float" type could cause
an internal error in RTLtyping/Machtyping.
- The case __builtin_fabs applied to integers was missing in the
C semantics and in C#minor generation.
- Fixed some type annotations on CompCert C expressions. These
annotations were incorrect but not in a way that impacted code
generation.
Release 2.2, 2014-02-24
=======================
Major improvements:
- Two new static analyses are performed on the RTL intermediate form:
. Value analysis, tracking constants, some integer range information,
and pointer aliasing information.
. Neededness analysis, generalizing liveness analysis to individual
bits of integer values and to stack memory locations.
- Improved RTL optimizations, exploiting the results of these analyses:
. Constant propagation can track constants across memory stores and loads.
. Common subexpression elimination exploits nonaliasing information.
. Dead code elimination can eliminate useless memory writes and
block copies, as well as integer operations that do not change
the needed bits.
. Redundant cast elimination is now performed globally (at
function level) rather than locally on individual expressions.
- Experimental support for defining and calling variable-argument functions,
including support for the <stdarg.h> interface.
(Option -fvararg-calls, "on" by default.)
Language features:
- In "switch" statements, "default" cases can now appear anywhere, not
just as the last case.
- Support for incomplete array as last field of a struct,
as specified in ISO C 99.
- Support for declarations within 'for' loops, as specified in ISO C 99.
(E.g. "for (int i = 0; i < 4; i++) ...")
- Revised semantics and implementation of _Alignas(N) attribute
to better match those of GCC and Clang.
- Better tolerance for functions declared without prototypes
(option -funprototyped, "on" by default).
- On PowerPC, support "far-data" sections
(register-relative addressing with 32-bit offsets).
Improvements in ABI conformance:
- For x86/IA32, align struct fields of types "double" or "long long" to 4
instead of 8, as prescribed by the x86 ELF ABI.
- For PowerPC and ARM, structs and unions returned as function results
are now passed in integer registers if their sizes are small enough
(<= 8 bytes for PowerPC, <= 4 bytes for ARM).
Usability:
- Revised parsing of command-line arguments to be closer to GCC and Clang.
In particular, "ccomp -c foo.c -o obj/foo.o" now works as expected,
instead of ignoring the "-o" option as in earlier CompCert versions.
- Recognize input files ending in .i and .p as C source files that
must not be preprocessed.
- Warn for uses of the following GCC extensions to ISO C:
zero-sized arrays, empty structs/unions, empty initializer braces.
- Option "-fno-fpu" to prevent the use of FP registers for some
integer operations such as block copies. (Replaces the previous
"-fno-sse" option which was x86/IA32-specific, and extends it to
PowerPC and ARM.)
- Option "-drtl" to record the RTL intermediate representation
at every stage of optimization. (Replaces "-dtailcall", "-dinlining",
"-dconstprop", and "-dcse".)
- Add CompCert version number and command-line arguments as comments
in the generated assembly files.
Other performance improvements:
- Recognize __builtin_fabs as a primitive unary operator instead of
a built-in function, enabling more optimizations.
- PowerPC: shorter code generated for "&global_variable + expr".
Improvements in compilation times:
- More efficient implementation of Kildall's dataflow equation solver,
reduces size of worklist and nomber of times a node is visited.
- Better OCaml GC settings significantly reduce compilation times
for very large source functions.
Bug fixing:
- Fixed incorrect hypothesis on __builtin_write{16,32}_reversed.
- Fixed syntax error in __attribute__((__packed__)).
- Emit clean compile-time error for 'switch' over a value of 64-bit
integer type (currently not supported).
- Recognize source files with .i or .p extension as C sources that
should not be preprocessed.
Coq development:
- Removed propositional extensionality axiom (prop_ext).
- Suppressed the Mfloat64al32 memory_chunk, no longer needed.
Release 2.1, 2013-10-28
=======================
Language semantics:
- More precise modeling of not-a-numbers (NaNs) in floating-point
arithmetic.
- The CompCert C language is now defined with reference to ISO C99
instead of ISO C90 ("ANSI C") as before. This affects mostly the
wording of the reference manual. However, the parsing of integer
constants and character constants was revised to follow the ISO C99
standard.
Language features:
- Support for _Alignas(N) attribute from ISO C 2011.
- Revised implementation of packed structs, taking advantage of _Alignas.
- Suppressed the pragma "packed", replaced by a struct-level attribute
__packed__(params) or __attribute__(packed(params)).
- Fixed typing rules for __builtin_annot() to avoid casting arguments
of small integer or FP types.
Performance improvements:
- Optimize integer divisions by positive constants, turning them into
multiply-high and shifts.
- Optimize floating-point divisions by powers of 2, turning them
into multiplications.
- Optimize "x * 2.0" and "2.0 * x" into "x + x".
- PowerPC: more efficient implementation of division on 64-bit integers.
Bug fixing:
- Fixed compile-time error when assigning a long long RHS to a bitfield.
- Avoid double rounding issues in conversion from 64-bit integers
to single-precision floats.
Miscellaneous:
- Minor simplifications in the generic solvers for dataflow analysis.
- Small improvements in compilation times for the register allocation pass.
- MacOS X port updated to the latest XCode (version 5.0).
Release 2.0, 2013-06-21
=======================
Major improvements:
- Support for C types "long long" and "unsigned long long", that is,
64-bit integers. Regarding arithmetic operations on 64-bit integers,
. simple operations are expanded in-line and proved correct;
. more complex operations (division, modulus, conversions to/from floats)
call into library functions written in assembly, heavily tested
but not yet proved correct.
- The register allocator was completely rewritten to use an "end-to-end"
translation validation approach, using a validation algorithm
described in the paper "Validating register allocation and spilling"
by Silvain Rideau and Xavier Leroy, Compiler Construction 2010,
http://dx.doi.org/10.1007/978-3-642-11970-5_13
This validation-based approach enables better register allocation, esp:
. live-range splitting is implemented
. two-address operations are treated more efficiently
. no need to reserve processor registers for spilling and reloading.
The improvements in quality of generated code is significant for
IA32 (because of its paucity of registers) but less so for ARM and PowerPC.
- Preliminary support for debugging information. The "-g" flag
causes DWARF debugging information to be generated for line numbers
and stack structure (Call Frame Information). With a debugger like
GDB, this makes it possible to step through the code, put breakpoints
by line number, and print stack backtraces. However, no information
is generated yet for C type definitions nor for variables; therefore,
it is not possible to print the values of variables.
Improvements in ABI conformance:
- For IA32 and ARM, function arguments of type "float"
(single-precision FP) were incorrectly passed as "double".
- For PowerPC, fixed alignment of "double" and "long long" arguments
passed on stack.
Improvements in code generation:
- More aggressive common subexpression elimination across some builtin
function calls, esp. annotations.
Improvements in compiler usability:
- Option -fno-taillcalls to turn off tail-call elimination.
(Some static analysis tools are confused by this optimization.)
- Reduced stack usage of the compiler by rewriting some key functions
in tail-recursive style.
- Reduced memory requirements of constant propagation pass by forgetting
compile-time approximations of dead variables.
- More careful elaboration of C struct and union types into CompCert C
types, avoiding behaviors exponential in the nesting of structs.
Bug fixing:
- Fixed parsing of labeled statements inside "switch" constructs,
which were causing syntax errors.
- The "->" operator applied to an array type was causing a type error.
- Nested conditional expressions "a ? (b ? c : d) : e" were causing
a compile-time error if "c", "d" and "e" had different types.
Coq development:
- Adapted the memory model to the needs of the VST project at Princeton:
. Memory block identifiers are now of type "positive" instead of "Z"
. Strengthened invariants in the definition of memory injections
and the specification of external calls.
- The LTL intermediate language is now a CFG of basic blocks.
- Suppressed the LTLin intermediate language, no longer used.
Release 1.13, 2013-03-12
========================
Language semantics:
- Comparisons involving pointers "one past" the end of a block are
now defined. (They used to be undefined behavior.)
(Contributed by Robbert Krebbers).
Language features:
- Arguments to __builtin_annot() that are compile-time constants
are now replaced by their (integer or float) value in the annotation
generated in the assembly file.
Improvements in performance:
- ARM and PowerPC ports: more efficient access to function parameters
that are passed on the call stack.
- ARM port; slightly better code generated for some indirect memory
accesses.
Bug fixing:
- Fixed a bug in the reference interpreter in -all mode causing some
reductions to be incorrectly merged.
- Wrong parsing of hexadecimal floating-point literals 0xMMMMpEEE.
Improvements in usability:
- Better error and warning messages for declarations of variables
of size >= 2^32 bits.
- Reference interpreter: more efficient exploration of states in -all mode.
Coq development:
- More efficient implementation of machine integers (module Integers)
taking advantage of bitwise operations defined in ZArith in Coq 8.4.
- Revised handling of return addresses in the Mach language
and the Stacking and Asmgen passes.
- A number of definitions that were opaque for no good reason are now
properly transparent.
Release 1.12.1, 2013-01-29
==========================
Ported to Coq 8.4pl1. Otherwise functionally identical to release 1.12.
Release 1.12, 2013-01-11
========================
Improvements in confidence:
- Floating-point literals are now parsed and converted to IEEE-754 binary
FP numbers using a provably-correct conversion function implemented on
top of the Flocq library.
Language semantics:
- Comparison between function pointers is now correctly defined
in the semantics of CompCert C (it was previously undefined behavior,
by mistake).
- Bit-fields of 'enum' type are now treated as either unsigned or signed,
whichever is able to represent all values of the enum.
(Previously: always signed.)
- The "&&" and "||" operators are now primitive in CompCert C and are
given explicit semantic rules, instead of being expressed in terms
of "_ ? _ : _" as in previous CompCert releases.
- Added a "Ebuiltin" expression form (invocation of built-in function)
to CompCert C, and a "Sbuiltin" statement form to Clight.
Used it to simplify the encoding of annotations, memcpy, and volatile
memory accesses.
Performance improvements:
- Better code generated for "&&" and "||" operators.
- More aggressive elimination of conditional branches during constant
propagation, taking better advantage of inferred constants.
Language features:
- By popular demand, "asm" statements for inline assembly are now supported
if the flag -finline-asm is set. Use with extreme caution, as the
semantic preservation proof assumes these statements have no effect
on the processor state.
Internal simplifications and reorganization:
- Clight, Csharpminor, Cminor: suppressed the "Econdition" conditional
expressions, no longer useful.
- Clight: a single loop form, the three C loops are derived forms.
- Clight: volatile memory accesses are materialized as builtin operations.
- Clight: removed dependencies on CompCert C syntax and semantics.
- New pass SimplLocals over Clight that replaces local scalar variables
whose address is never taken by temporary, nonadressable variables.
(This used to be done in Cminorgen.)
- Csharpminor: simplified semantics.
- Cminor: suppressed the "Oboolval" and "Onotbool" operators,
which can be expressed in terms of "Ocmpu" at no performance costs.
- All languages: programs are now presented as a list of global definitions
(of functions or variables) instead of two lists, one for functions
and the other for variables.
Other changes:
- For compatibility with other C compilers, output files are now generated
in the current directory, by default; output file name can be controlled
with the -o option, somewhat like with GCC.
- Reference interpreter: better handling of volatile memory accesses.
- IA32/MacOS X: now supports referencing global variables defined in shared
libraries; old hack for stdio is no longer needed.
- PowerPC/MacOS X: this port was removed, as recent version of MacOS X
no longer support PowerPC.
Release 1.11, 2012-07-13
========================
Improvements in confidence:
- Floating-point numbers and arithmetic operations, previously axiomatized,
are now implemented and proved correct in Coq, using the Flocq library
of S. Boldo and G. Melquiond.
Language semantics:
- In accordance with ISO C standards, the signed division min_int / -1
and the signed remainder min_int % -1 (where min_int is the smallest
representable signed integer) now have undefined semantics and are
treated as "going wrong" behaviors.
(Previously, they were defined with results min_int and 0 respectively,
but this behavior requires unnatural code to be generated on IA32 and
PowerPC.)
Performance improvements:
- Function inlining is now implemented. The functions that are inlined
are those declared "inline" in the C source, provided they are not
recursive.
- Constant propagation is now able to propagate the initial values of
"const" global variables.
- Added option -ffloat-const-prop to control the propagation of
floating-point constants; see user's manual for documentation.
- Common subexpression elimination can now eliminate memory loads
following a memory store at the same location.
- ARM: make use of the "fcmpzd" and "fmdrr" instructions.
New tool:
- The "cchecklink" tool performs a posteriori validation of the
assembling and linking phases. It is available for PowerPC-EABI
only. It takes as inputs an ELF-PowerPC executable as produced
by the linker, as well as .sdump files (abstract assembly) as
produced by "ccomp -sdump", and checks that the executable contains
properly-assembled and linked code and data corresponding to those
produced by CompCert.
Other changes:
- Elimination of "static" functions and "static" global variables that
are not referenced in the generated code.
- The memory model was enriched with "max" permissions in addition to
"current" permissions, to better reason over "const" blocks and
already-deallocated blocks.
- More efficient implementation of the memory model, resulting
in faster interpretation of source files by "ccomp -interp".
- Added option "-falign-functions" to control alignment of function code.
Release 1.10, 2012-03-13
========================
Improvements in confidence:
- CompCert C now natively supports volatile types. Its semantics fully
specifies the meaning of volatile memory accesses. The translation
of volatile accesses to built-in function invocations is now proved correct.
- CompCert C now natively supports assignment between composite types
(structs or unions), passing composite types by value as function
parameters, and other instances of using composites as r-values, with
the exception of returning composites by value from a function.
(The latter remains emulated, using the -fstruct-return option.)
- PowerPC: removed the -fmadd option, not semantically-preserving
in the strict sense.
Language features:
- Support for _Bool type from ISO C99.
- Support for _Alignof(ty) operator from ISO C 2011
and __alignof__(ty), __alignof__(expr) from GCC.
Performance improvements:
- Improvements in instruction selection, especially for integer casts
and their combinations with bitwise operations.
- Shorter, more efficient code generated for accessing volatile global
variables.
- Better code generated for the && and || operators.
- More aggressive common subexpression elimination (CSE) of memory loads.
- Improved register allocation for invocations of built-ins,
especially for annotations.
- In Cminor and down, make safe operators non-strict: they return Vundef
instead of getting stuck. This enables more optimizations.
- Cast optimization is no longer performed by a separate pass over
RTL, but equivalent optimization is done during Cminor generation
and during instruction selection.
Other improvements:
- PowerPC/EABI: uninitialized global variables now go in common (bss) section.
- PowerPC: work around limited excursion of conditional branch instructions.
- PowerPC: added __builtin_fnmadd() and __builtin_fnmsub().
- Reference interpreter: better printing of pointer values and locations.
- Added command-line options -Wp,<opt> -Wa,<opt> -Wl,<opt> to pass
specific options to the preprocessor, assembler, or linker, respectively.
- More complete Cminor parser and printer (contributed by Andrew Tolmach).
Release 1.9.1, 2011-11-28
=========================
Bug fixes:
- Initialization of a char array by a short string literal was wrongly rejected
- Incorrect handling of volatile arrays.
- IA32 code generator: make sure that min_int / -1 does not cause a
machine trap.
Improvements:
- Added language option -flongdouble to treat "long double" like "double".
- The reference interpreter (ccomp -interp) now supports 2-argument main
functions (int main(int, char **)).
- Improved but still very experimental emulation of packed structs
(-fpacked-structs)
- Coq->Caml extraction: extract Coq pairs to Caml pairs and Coq
characters to Caml "char" type.
Release 1.9, 2011-08-22
=======================
- The reduction semantics of CompCert C was made executable and turned
into a reference interpreter for CompCert C, enabling animation of
the semantics. (Thanks to Brian Campbell for suggesting this approach.)
Usage is: ccomp -interp [options] source.c
Options include:
-trace to print a detailed trace of reduction steps
-random to randomize execution order
-all to explore all possible execution orders in parallel
- Revised and strengthened the top-level statements of semantic preservation.
In particular, we now show:
. backward simulation for the whole compiler without assuming
a deterministic external world;
. if the source program goes wrong after performing some I/O,
the compiled code performs at least these I/O before continuing
with an arbitrary behavior.
- Fixed two omissions in the semantics of CompCert C
(reported by Brian Campbell):
. Functions calls through a function pointer had undefined semantics.
. Conditional expressions "e1 ? e2 : e3" where e2 and e3 have different
types were missing a cast to their common type.
- Support for "read-modify-write" operations over volatiles
(such as e++ or --e or e |= 1 where e has volatile type)
through a new presimplification (flag -fvolatile-rmw, "on" by default).
- New optimization pass: Redundant Reload Elimination, which fixes up
inefficiencies introduced during the Reload pass. On x86, it increases
performance by up to 10%. On PowerPC and ARM, the effect is negligible.
- Revised handling of annotation statements. Now they come in two forms:
1. __builtin_annot("format", x1, ..., xN)
(arbitrarily many arguments; no code generated, even if some
of the xi's were spilled; no return value)
2. __builtin_annot_intval("format", x1)
(one integer argument, reloaded in a register if needed,
returned as result).
- Related clean-ups in the handling of external functions and
compiler built-ins. In particular, __builtin_memcpy is now
fully specified.
- ARM code generator was ported to the new ABI (EABI in ARM parlance,
armel in Debian parlance), using VFD instructions for floating-point.
(Successfully tested on a Trimslice platform running Ubuntu 11.04.)
- IA32 code generator:
. Added -fno-sse option to prevent generation of SSE instructions
for memory copy operations.
. More realistic modeling of the ST0 (top-of-FP-stack) register
and of floating-point compare and branch.
- PowerPC code generator: more efficient instruction sequences generated
for insertion in a bit field and for some comparisons against 0.
Release 1.8.2, 2011-05-24
=========================
- Support for "aligned" and "section" attributes on global variables, e.g.
__attribute__((aligned(16))) int x;
- Experimental emulation of packed structs (flag -fpacked-structs).
- Pointer comparisons now treated as unsigned comparisons (previously: signed).
This fixes an issue with arrays straddling the 0x8000_0000 boundary.
Consequently, the "ofs" part of pointer values "Vptr b ofs" is
now treated as unsigned (previously: signed).
- Elimination of unreferenced labels now performed by a separate pass
(backend/CleanupLabels.v) and proved correct.
- Stacking pass revised: supports more flexible layout of the stack
frame; two-step proof (Stackingproof + Machabstr2concr) merged
into one single proof (Stackingproof).
- The requirement that pointers be valid in pointer comparisons
was pushed through all intermediate languages of the back-end
(previously: requirement present only up to Csharpminor).
- Emulation of assignment between structs and between unions was
simplified and made more efficient, thanks to a better implementation
of __builtin_memcpy.
- Improvements to the compiler driver:
. -E option now prints preprocessed result to standard output
instead of saving it in a .i file
. support for .s (assembly) and .S (assembly to be preprocessed)
input files
Release 1.8.1, 2011-03-14
=========================
- Adapted to Coq 8.3pl1.
- Reduced compilation times through several algorithmic improvements
(contributed by A. Pilkiewicz).
- In the various semantics, allow float-to-int conversions to fail
(if the float argument is outside the range of representable ints).
- Initialization of global C variables made more robust and proved correct.
- ABI conformance improved:
. the "char" type is now signed for x86, remains unsigned for PowerPC and ARM
. placement of bit-fields now follows SVR4 conventions (affects PowerPC)
- Bug fixes in the C pre-simplifier:
. nontermination with some recursive struct types
. issues with zero-width bit fields
. elimination of struct assignments duplicating some volatile accesses
Release 1.8, 2010-09-21
=======================
- The input language to the proved part of the compiler is no longer
Clight but CompCert C: a larger subset of the C language supporting
in particular side-effects within expressions. The transformations
that pull side effects out of expressions and materialize implicit
casts, formerly performed by untrusted Caml code, are now fully
proved in Coq.
- New port targeting Intel/AMD x86 processors. Generates 32-bit x86 code
using SSE2 extensions for floating-point arithmetic. Works under
Linux, MacOS X, and the Cygwin environment for Windows.
CompCert's compilation strategy is not a very good match for the
x86 architecture, therefore the performance of the generated code
is not as good as for the PowerPC port, but still usable.
(About 75% of the performance of gcc -O1 for x86, compared with
> 90% for PowerPC.)
- More faithful semantics for volatile accesses:
. volatile reads and writes from a volatile global variable are treated
like input and output system calls (respectively), bypassing
the memory model entirely;
. volatile reads and writes from other locations are treated like
regular loads and stores.
- Introduced __builtin_memcpy() and __builtin_memcpy_words(), use them
instead of memcpy() to compile struct and union assignments.
- Introduced __builtin_annotation() to transmit assertions from
the source program all the way to the generated assembly code.
- Elimination of some useless casts around "&", "|" and "^" bitwise operators.
- Produce fewer "moves" during RTL generation. This speeds up the
rest of compilation and slightly improves the result of register
allocation when register pressure is high.
- Improvements in register allocation:
. Implemented a spilling heuristic during register allocation.
This heuristic reduces significantly the amount of spill code
generated when register pressure is high.
. More coalescing between low-pressure and high-pressure variables.
. Aggressive coalescing between pairs of spilled variables.
- Fixed some bugs in the emulation of bit fields.
Release 1.7.1, 2010-04-13
=========================
Bug fixes in the new C pre-simplifier:
- Missing cast on return value for some functions
- Incorrect simplification of some uses of || and &&
- Nontermination in the presence of a bit field of size exactly 32 bits.
- Global initializers for structs containing bit fields.
- Wrong type in volatile reads from variables of type 'unsigned int'.
Small improvements to the PowerPC port:
- Added __builtin_trap() built-in function.
- Support for '#pragma reserve_register' (EABI)
- Less aggressive alignment of global variables.
- Generate '.type' and '.size' directives (EABI).
Release 1.7, 2010-03-31
=======================
- New implementation of the C type-checker, simplifier, and translation to
Clight. Compared with the previous CIL-based solution, the new
implementation is more modular and supports more optional simplifications.
- More features of the C language are handled by expansion during
translation to Clight:
. assignment between structs and unions (option -fstruct-assign)
. passing structs and union by value (option -fstruct-passing)
. bit-fields in structs (option -fbitfields)
- The "volatile" modifier is now honored. Volatile accesses are represented
in Clight by calls to built-in functions, which are preserved throughout
the compilation chain, then turned into processor loads and stores
at the end.
- Generic support for C built-in functions. These predefined external
functions give access to special instructions of the processor. See
powerpc/CBuiltins.ml for the list of PowerPC built-in functions.
- The memory model now exposes the bit-level in-memory representation
of integers and floats. This strengthens the semantic preservation
theorem: we now prove that C code that directly manipulates these
bit-level representations (e.g. via a union between floats and integers)
is correctly compiled.
- The memory model now supports fine-grained access control to individual
bytes of a memory block. This feature is currently unused in the
compiler proofs, but will facilitate connections with separation logics
later.
- External functions are now allowed to read and modify memory.
The semantic preservation proofs were strengthened accordingly.
In particular, this enables the malloc() and free() C library functions
to be modeled as external functions in a provably correct manner.
- Minor improvements in the handling of global environments and the
construction of the initial memory state.
- Bug fixes in the handling of '#pragma section' and '#pragma set_section'.
- The C test suite was enriched and restructured.
Release 1.6, 2010-01-13
=======================
- Support Clight initializers of the form "int * x = &y;".
- Fixed spurious compile-time error on Clight initializers of the form
"const enum E x[2] = { E_1, E_2 };".
- Produce informative error message if a 'return' without argument
occurs in a non-void function, or if a 'return' with an argument
occurs in a void function.
- Preliminary support for '#pragma section' and '#pragma set_section'.
- Preliminary support for small data areas in PowerPC code generator.
- Back-end: added support for jump tables; used them to compile
dense 'switch' statements.
- PowerPC code generator: force conversion to single precision before
doing a "store single float" instruction.
Release 1.5, 2009-08-28
=======================