Skip to content

Commit

Permalink
[mlir][math] powf(a, b) drop support when a < 0 (#126338)
Browse files Browse the repository at this point in the history 
Related: #124402

- change inefficient implementation of `powf(a, b)` to handle `a < 0`
case
  - thus drop `a < 0` case support

However, some special cases are being used such as:
  - `a < 0` and `b = 0, b = 0.5, b = 1 or b = 2`
  - convert those special cases into simpler ops.
  • Loading branch information
@ita9naiwa
ita9naiwa authored Feb 13, 2025
1 parent a1345eb commit de09986
Show file tree
Hide file tree
Showing 3 changed files with 188 additions and 118 deletions.
92 changes: 62 additions & 30 deletions mlir/lib/Dialect/Math/Transforms/ExpandPatterns.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@
#include "mlir/IR/ImplicitLocOpBuilder.h"
#include "mlir/IR/TypeUtilities.h"
#include "mlir/Transforms/DialectConversion.h"
#include "llvm/ADT/APFloat.h"

using namespace mlir;

Expand Down Expand Up @@ -311,40 +312,71 @@ static LogicalResult convertFPowIOp(math::FPowIOp op,
return success();
}

// Converts Powf(float a, float b) (meaning a^b) to exp^(b * ln(a))
// Converts Powf(float a, float b) (meaning a^b) to exp^(b * ln(a))
// Some special cases where b is constant are handled separately:
// when b == 0, or |b| == 0.5, 1.0, or 2.0.
static LogicalResult convertPowfOp(math::PowFOp op, PatternRewriter &rewriter) {
ImplicitLocOpBuilder b(op->getLoc(), rewriter);
Value operandA = op.getOperand(0);
Value operandB = op.getOperand(1);
Type opType = operandA.getType();
Value zero = createFloatConst(op->getLoc(), opType, 0.00, rewriter);
Value one = createFloatConst(op->getLoc(), opType, 1.00, rewriter);
Value two = createFloatConst(op->getLoc(), opType, 2.00, rewriter);
Value negOne = createFloatConst(op->getLoc(), opType, -1.00, rewriter);
Value opASquared = b.create<arith::MulFOp>(opType, operandA, operandA);
Value opBHalf = b.create<arith::DivFOp>(opType, operandB, two);

Value logA = b.create<math::LogOp>(opType, opASquared);
Value mult = b.create<arith::MulFOp>(opType, opBHalf, logA);
Value expResult = b.create<math::ExpOp>(opType, mult);
Value negExpResult = b.create<arith::MulFOp>(opType, expResult, negOne);
Value remainder = b.create<arith::RemFOp>(opType, operandB, two);
Value negCheck =
b.create<arith::CmpFOp>(arith::CmpFPredicate::OLT, operandA, zero);
Value oddPower =
b.create<arith::CmpFOp>(arith::CmpFPredicate::ONE, remainder, zero);
Value oddAndNeg = b.create<arith::AndIOp>(op->getLoc(), oddPower, negCheck);

// First, we select between the exp value and the adjusted value for odd
// powers of negatives. Then, we ensure that one is produced if `b` is zero.
// This corresponds to `libm` behavior, even for `0^0`. Without this check,
// `exp(0 * ln(0)) = exp(0 *-inf) = exp(-nan) = -nan`.
Value zeroCheck =
b.create<arith::CmpFOp>(arith::CmpFPredicate::OEQ, operandB, zero);
Value res = b.create<arith::SelectOp>(op->getLoc(), oddAndNeg, negExpResult,
expResult);
res = b.create<arith::SelectOp>(op->getLoc(), zeroCheck, one, res);
rewriter.replaceOp(op, res);
auto typeA = operandA.getType();
auto typeB = operandB.getType();

auto &sem =
cast<mlir::FloatType>(getElementTypeOrSelf(typeB)).getFloatSemantics();
APFloat valueB(sem);
if (matchPattern(operandB, m_ConstantFloat(&valueB))) {
if (valueB.isZero()) {
// a^0 -> 1
Value one = createFloatConst(op->getLoc(), typeA, 1.0, rewriter);
rewriter.replaceOp(op, one);
return success();
}
if (valueB.isExactlyValue(1.0)) {
// a^1 -> a
rewriter.replaceOp(op, operandA);
return success();
}
if (valueB.isExactlyValue(-1.0)) {
// a^(-1) -> 1 / a
Value one = createFloatConst(op->getLoc(), typeA, 1.0, rewriter);
Value div = b.create<arith::DivFOp>(one, operandA);
rewriter.replaceOp(op, div);
return success();
}
if (valueB.isExactlyValue(0.5)) {
// a^(1/2) -> sqrt(a)
Value sqrt = b.create<math::SqrtOp>(operandA);
rewriter.replaceOp(op, sqrt);
return success();
}
if (valueB.isExactlyValue(-0.5)) {
// a^(-1/2) -> 1 / sqrt(a)
Value rsqrt = b.create<math::RsqrtOp>(operandA);
rewriter.replaceOp(op, rsqrt);
return success();
}
if (valueB.isExactlyValue(2.0)) {
// a^2 -> a * a
Value mul = b.create<arith::MulFOp>(operandA, operandA);
rewriter.replaceOp(op, mul);
return success();
}
if (valueB.isExactlyValue(-2.0)) {
// a^(-2) -> 1 / (a * a)
Value mul = b.create<arith::MulFOp>(operandA, operandA);
Value one =
createFloatConst(op->getLoc(), operandA.getType(), 1.0, rewriter);
Value div = b.create<arith::DivFOp>(one, mul);
rewriter.replaceOp(op, div);
return success();
}
}

Value logA = b.create<math::LogOp>(operandA);
Value mult = b.create<arith::MulFOp>(operandB, logA);
Value expResult = b.create<math::ExpOp>(mult);
rewriter.replaceOp(op, expResult);
return success();
}

Expand Down
145 changes: 88 additions & 57 deletions mlir/test/Dialect/Math/expand-math.mlir
View file
Original file line number Diff line number Diff line change
Expand Up @@ -201,26 +201,86 @@ func.func @roundf_func(%a: f32) -> f32 {
// -----

// CHECK-LABEL: func @powf_func
// CHECK-SAME: ([[ARG0:%.+]]: f64, [[ARG1:%.+]]: f64)
func.func @powf_func(%a: f64, %b: f64) ->f64 {
// CHECK-DAG: [[CST0:%.+]] = arith.constant 0.000000e+00
// CHECK-DAG: [[CST1:%.+]] = arith.constant 1.0
// CHECK-DAG: [[TWO:%.+]] = arith.constant 2.000000e+00
// CHECK-DAG: [[NEGONE:%.+]] = arith.constant -1.000000e+00
// CHECK-DAG: [[SQR:%.+]] = arith.mulf [[ARG0]], [[ARG0]]
// CHECK-DAG: [[HALF:%.+]] = arith.divf [[ARG1]], [[TWO]]
// CHECK-DAG: [[LOG:%.+]] = math.log [[SQR]]
// CHECK-DAG: [[MULT:%.+]] = arith.mulf [[HALF]], [[LOG]]
// CHECK-DAG: [[EXPR:%.+]] = math.exp [[MULT]]
// CHECK-DAG: [[NEGEXPR:%.+]] = arith.mulf [[EXPR]], [[NEGONE]]
// CHECK-DAG: [[REMF:%.+]] = arith.remf [[ARG1]], [[TWO]]
// CHECK-DAG: [[CMPNEG:%.+]] = arith.cmpf olt, [[ARG0]]
// CHECK-DAG: [[CMPZERO:%.+]] = arith.cmpf one, [[REMF]]
// CHECK-DAG: [[AND:%.+]] = arith.andi [[CMPZERO]], [[CMPNEG]]
// CHECK-DAG: [[CMPZERO:%.+]] = arith.cmpf oeq, [[ARG1]], [[CST0]]
// CHECK-DAG: [[SEL:%.+]] = arith.select [[AND]], [[NEGEXPR]], [[EXPR]]
// CHECK-DAG: [[SEL1:%.+]] = arith.select [[CMPZERO]], [[CST1]], [[SEL]]
// CHECK: return [[SEL1]]
// CHECK-SAME: (%[[ARG0:.+]]: f64, %[[ARG1:.+]]: f64) -> f64
func.func @powf_func(%a: f64, %b: f64) -> f64 {
// CHECK: %[[LOGA:.+]] = math.log %[[ARG0]] : f64
// CHECK: %[[MUL:.+]] = arith.mulf %[[ARG1]], %[[LOGA]] : f64
// CHECK: %[[EXP:.+]] = math.exp %[[MUL]] : f64
// CHECK: return %[[EXP]] : f64
%ret = math.powf %a, %b : f64
return %ret : f64
}

// CHECK-LABEL: func @powf_func_zero
// CHECK-SAME: (%[[ARG0:.+]]: f64) -> f64
func.func @powf_func_zero(%a: f64) -> f64{
// CHECK: %[[ONE:.+]] = arith.constant 1.000000e+00 : f64
// CHECK: return %[[ONE]] : f64
%b = arith.constant 0.0 : f64
%ret = math.powf %a, %b : f64
return %ret : f64
}

// CHECK-LABEL: func @powf_func_one
// CHECK-SAME: (%[[ARG0:.+]]: f64) -> f64
func.func @powf_func_one(%a: f64) -> f64{
// CHECK: return %[[ARG0]] : f64
%b = arith.constant 1.0 : f64
%ret = math.powf %a, %b : f64
return %ret : f64
}

// CHECK-LABEL: func @powf_func_negone
// CHECK-SAME: (%[[ARG0:.+]]: f64) -> f64
func.func @powf_func_negone(%a: f64) -> f64{
// CHECK: %[[CSTONE:.+]] = arith.constant 1.000000e+00 : f64
// CHECK: %[[DIV:.+]] = arith.divf %[[CSTONE]], %[[ARG0]] : f64
// CHECK: return %[[DIV]] : f64
%b = arith.constant -1.0 : f64
%ret = math.powf %a, %b : f64
return %ret : f64
}

// CHECK-LABEL: func @powf_func_half
// CHECK-SAME: (%[[ARG0:.+]]: f64) -> f64
func.func @powf_func_half(%a: f64) -> f64{
// CHECK: %[[SQRT:.+]] = math.sqrt %[[ARG0]] : f64
// CHECK: return %[[SQRT]] : f64
%b = arith.constant 0.5 : f64
%ret = math.powf %a, %b : f64
return %ret : f64
}

// CHECK-LABEL: func @powf_func_neghalf
// CHECK-SAME: (%[[ARG0:.+]]: f64) -> f64
func.func @powf_func_neghalf(%a: f64) -> f64{
// CHECK: %[[CSTONE:.+]] = arith.constant 1.000000e+00 : f64
// CHECK: %[[SQRT:.+]] = math.sqrt %[[ARG0]] : f64
// CHECK: %[[DIV:.+]] = arith.divf %[[CSTONE]], %[[SQRT]] : f64
// CHECK: return %[[DIV]] : f64
%b = arith.constant -0.5 : f64
%ret = math.powf %a, %b : f64
return %ret : f64
}

// CHECK-LABEL: func @powf_func_two
// CHECK-SAME: (%[[ARG0:.+]]: f64) -> f64
func.func @powf_func_two(%a: f64) -> f64{
// CHECK: %[[MUL:.+]] = arith.mulf %[[ARG0]], %[[ARG0]] : f64
// CHECK: return %[[MUL]] : f64
%b = arith.constant 2.0 : f64
%ret = math.powf %a, %b : f64
return %ret : f64
}

// CHECK-LABEL: func @powf_func_negtwo
// CHECK-SAME: (%[[ARG0:.+]]: f64) -> f64
func.func @powf_func_negtwo(%a: f64) -> f64{
// CHECK-DAG: %[[MUL:.+]] = arith.mulf %[[ARG0]], %[[ARG0]] : f64
// CHECK-DAG: %[[CSTONE:.+]] = arith.constant 1.000000e+00 : f64
// CHECK: %[[DIV:.+]] = arith.divf %[[CSTONE]], %[[MUL]] : f64
// CHECK: return %[[DIV]] : f64
%b = arith.constant -2.0 : f64
%ret = math.powf %a, %b : f64
return %ret : f64
}
Expand Down Expand Up @@ -602,26 +662,11 @@ func.func @math_fpowi_to_powf_tensor(%0 : tensor<8xf32>, %1: tensor<8xi32>) -> t
return %2 : tensor<8xf32>
}
// CHECK-SAME: (%[[ARG0:.*]]: tensor<8xf32>, %[[ARG1:.*]]: tensor<8xi32>) -> tensor<8xf32> {
// CHECK-DAG: %[[CSTNEG1:.*]] = arith.constant dense<-1.000000e+00> : tensor<8xf32>
// CHECK-DAG: %[[CST2:.*]] = arith.constant dense<2.000000e+00> : tensor<8xf32>
// CHECK-DAG: %[[CST0:.*]] = arith.constant dense<0.000000e+00> : tensor<8xf32>
// CHECK-DAG: %[[CST1:.+]] = arith.constant dense<1.000000e+00> : tensor<8xf32>
// CHECK: %[[TOFP:.*]] = arith.sitofp %[[ARG1]] : tensor<8xi32> to tensor<8xf32>
// CHECK: %[[SQ:.*]] = arith.mulf %[[ARG0]], %[[ARG0]] : tensor<8xf32>
// CHECK: %[[DIV:.*]] = arith.divf %[[TOFP]], %[[CST2]] : tensor<8xf32>
// CHECK: %[[LG:.*]] = math.log %[[SQ]] : tensor<8xf32>
// CHECK: %[[MUL:.*]] = arith.mulf %[[DIV]], %[[LG]] : tensor<8xf32>
// CHECK: %[[EXP:.*]] = math.exp %[[MUL]] : tensor<8xf32>
// CHECK: %[[MUL1:.*]] = arith.mulf %[[EXP]], %[[CSTNEG1]] : tensor<8xf32>
// CHECK: %[[REM:.*]] = arith.remf %[[TOFP]], %[[CST2]] : tensor<8xf32>
// CHECK: %[[CMPF:.*]] = arith.cmpf olt, %[[ARG0]], %[[CST0]] : tensor<8xf32>
// CHECK: %[[CMPF1:.*]] = arith.cmpf one, %[[REM]], %[[CST0]] : tensor<8xf32>
// CHECK: %[[AND:.*]] = arith.andi %[[CMPF1]], %[[CMPF]] : tensor<8xi1>
// CHECK: %[[CMPZERO:.*]] = arith.cmpf oeq, %[[TOFP]], %[[CST0]]
// CHECK: %[[SEL:.*]] = arith.select %[[AND]], %[[MUL1]], %[[EXP]] : tensor<8xi1>, tensor<8xf32>
// CHECK: %[[SEL1:.+]] = arith.select %[[CMPZERO]], %[[CST1]], %[[SEL]]
// CHECK: return %[[SEL1]] : tensor<8xf32>

// CHECK: %[[TOFP:.*]] = arith.sitofp %[[ARG1]] : tensor<8xi32> to tensor<8xf32>
// CHECK: %[[LOGA:.*]] = math.log %[[ARG0]] : tensor<8xf32>
// CHECK: %[[MUL:.*]] = arith.mulf %[[TOFP]], %[[LOGA]] : tensor<8xf32>
// CHECK: %[[EXP:.*]] = math.exp %[[MUL]] : tensor<8xf32>
// CHECK: return %[[EXP]]
// -----

// CHECK-LABEL: func.func @math_fpowi_to_powf_scalar
Expand All @@ -630,25 +675,11 @@ func.func @math_fpowi_to_powf_scalar(%0 : f32, %1: i64) -> f32 {
return %2 : f32
}
// CHECK-SAME: (%[[ARG0:.*]]: f32, %[[ARG1:.*]]: i64) -> f32 {
// CHECK-DAG: %[[CSTNEG1:.*]] = arith.constant -1.000000e+00 : f32
// CHECK-DAG: %[[CST2:.*]] = arith.constant 2.000000e+00 : f32
// CHECK-DAG: %[[CST0:.*]] = arith.constant 0.000000e+00 : f32
// CHECK-DAG: %[[CST1:.+]] = arith.constant 1.000000e+00 : f32
// CHECK: %[[TOFP:.*]] = arith.sitofp %[[ARG1]] : i64 to f32
// CHECK: %[[SQ:.*]] = arith.mulf %[[ARG0]], %[[ARG0]] : f32
// CHECK: %[[DIV:.*]] = arith.divf %[[TOFP]], %[[CST2]] : f32
// CHECK: %[[LG:.*]] = math.log %[[SQ]] : f32
// CHECK: %[[MUL:.*]] = arith.mulf %[[DIV]], %[[LG]] : f32
// CHECK: %[[LOGA:.*]] = math.log %[[ARG0]] : f32
// CHECK: %[[MUL:.*]] = arith.mulf %[[TOFP]], %[[LOGA]] : f32
// CHECK: %[[EXP:.*]] = math.exp %[[MUL]] : f32
// CHECK: %[[MUL1:.*]] = arith.mulf %[[EXP]], %[[CSTNEG1]] : f32
// CHECK: %[[REM:.*]] = arith.remf %[[TOFP]], %[[CST2]] : f32
// CHECK: %[[CMPF:.*]] = arith.cmpf olt, %[[ARG0]], %[[CST0]] : f32
// CHECK: %[[CMPF1:.*]] = arith.cmpf one, %[[REM]], %[[CST0]] : f32
// CHECK: %[[AND:.*]] = arith.andi %[[CMPF1]], %[[CMPF]] : i1
// CHECK: %[[CMPZERO:.*]] = arith.cmpf oeq, %[[TOFP]], %[[CST0]]
// CHECK: %[[SEL:.*]] = arith.select %[[AND]], %[[MUL1]], %[[EXP]] : f32
// CHECK: %[[SEL1:.+]] = arith.select %[[CMPZERO]], %[[CST1]], %[[SEL]]
// CHECK: return %[[SEL1]] : f32
// CHECK: return %[[EXP]] : f32

// -----

Expand Down
69 changes: 38 additions & 31 deletions mlir/test/mlir-runner/test-expand-math-approx.mlir
View file
Original file line number Diff line number Diff line change
Expand Up @@ -202,55 +202,62 @@ func.func @powf() {
%a_p = arith.constant 2.0 : f64
call @func_powff64(%a, %a_p) : (f64, f64) -> ()

// CHECK-NEXT: -27
%b = arith.constant -3.0 : f64
%b_p = arith.constant 3.0 : f64
call @func_powff64(%b, %b_p) : (f64, f64) -> ()

// CHECK-NEXT: 2.343
%c = arith.constant 2.343 : f64
%c_p = arith.constant 1.000 : f64
call @func_powff64(%c, %c_p) : (f64, f64) -> ()
%b = arith.constant 2.343 : f64
%b_p = arith.constant 1.000 : f64
call @func_powff64(%b, %b_p) : (f64, f64) -> ()

// CHECK-NEXT: 0.176171
%d = arith.constant 4.25 : f64
%d_p = arith.constant -1.2 : f64
call @func_powff64(%d, %d_p) : (f64, f64) -> ()
%c = arith.constant 4.25 : f64
%c_p = arith.constant -1.2 : f64
call @func_powff64(%c, %c_p) : (f64, f64) -> ()

// CHECK-NEXT: 1
%e = arith.constant 4.385 : f64
%e_p = arith.constant 0.00 : f64
call @func_powff64(%e, %e_p) : (f64, f64) -> ()
%d = arith.constant 4.385 : f64
%d_p = arith.constant 0.00 : f64
call @func_powff64(%d, %d_p) : (f64, f64) -> ()

// CHECK-NEXT: 6.62637
%f = arith.constant 4.835 : f64
%f_p = arith.constant 1.2 : f64
call @func_powff64(%f, %f_p) : (f64, f64) -> ()
%e = arith.constant 4.835 : f64
%e_p = arith.constant 1.2 : f64
call @func_powff64(%e, %e_p) : (f64, f64) -> ()

// CHECK-NEXT: nan
%i = arith.constant 1.0 : f64
%h = arith.constant 0x7fffffffffffffff : f64
call @func_powff64(%i, %h) : (f64, f64) -> ()
%f = arith.constant 1.0 : f64
%f_p = arith.constant 0x7fffffffffffffff : f64
call @func_powff64(%f, %f_p) : (f64, f64) -> ()

// CHECK-NEXT: inf
%j = arith.constant 29385.0 : f64
%j_p = arith.constant 23598.0 : f64
call @func_powff64(%j, %j_p) : (f64, f64) -> ()
%g = arith.constant 29385.0 : f64
%g_p = arith.constant 23598.0 : f64
call @func_powff64(%g, %g_p) : (f64, f64) -> ()

// CHECK-NEXT: -nan
%k = arith.constant 1.0 : f64
%k_p = arith.constant 0xfff0000001000000 : f64
call @func_powff64(%k, %k_p) : (f64, f64) -> ()
%h = arith.constant 1.0 : f64
%h_p = arith.constant 0xfff0000001000000 : f64
call @func_powff64(%h, %h_p) : (f64, f64) -> ()

// CHECK-NEXT: -nan
%l = arith.constant 1.0 : f32
%l_p = arith.constant 0xffffffff : f32
call @func_powff32(%l, %l_p) : (f32, f32) -> ()
%i = arith.constant 1.0 : f32
%i_p = arith.constant 0xffffffff : f32
call @func_powff32(%i, %i_p) : (f32, f32) -> ()

// CHECK-NEXT: 1
%zero = arith.constant 0.0 : f32
call @func_powff32(%zero, %zero) : (f32, f32) -> ()
%j = arith.constant 0.000 : f32
%j_r = math.powf %j, %j : f32
vector.print %j_r : f32

// CHECK-NEXT: 4
%k = arith.constant -2.0 : f32
%k_p = arith.constant 2.0 : f32
%k_r = math.powf %k, %k_p : f32
vector.print %k_r : f32

// CHECK-NEXT: 0.25
%l = arith.constant -2.0 : f32
%l_p = arith.constant -2.0 : f32
%l_r = math.powf %k, %l_p : f32
vector.print %l_r : f32
return
}

Expand Down

0 comments on commit de09986

Please sign in to comment.