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interpreter: removes unneeded stack walks #2274

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Jun 27, 2024
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interpreter: removes unneeded stack walks #2274

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78 changes: 38 additions & 40 deletions internal/engine/interpreter/compiler.go
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Original file line number Diff line number Diff line change
Expand Up @@ -26,11 +26,14 @@ const (
type (
controlFrame struct {
frameID uint32
// originalStackLen holds the number of values on the stack
// originalStackLenWithoutParam holds the number of values on the stack
// when Start executing this control frame minus params for the block.
originalStackLenWithoutParam int
blockType *wasm.FunctionType
kind controlFrameKind
// originalStackLenWithoutParamUint64 is almost the same as originalStackLenWithoutParam
// except that it holds the number of values on the stack in uint64.
originalStackLenWithoutParamUint64 int
blockType *wasm.FunctionType
kind controlFrameKind
}
controlFrames struct{ frames []controlFrame }
)
Expand Down Expand Up @@ -157,9 +160,11 @@ type compiler struct {
enabledFeatures api.CoreFeatures
callFrameStackSizeInUint64 int
stack []unsignedType
currentFrameID uint32
controlFrames controlFrames
unreachableState struct {
// stackLenInUint64 is the length of the stack in uint64.
stackLenInUint64 int
currentFrameID uint32
controlFrames controlFrames
unreachableState struct {
on bool
depth int
}
Expand Down Expand Up @@ -341,6 +346,7 @@ func (c *compiler) Next() (*compilationResult, error) {
c.pc = 0
c.currentOpPC = 0
c.currentFrameID = 0
c.stackLenInUint64 = 0
c.unreachableState.on, c.unreachableState.depth = false, 0

if err := c.compile(sig, code.Body, code.LocalTypes, code.BodyOffsetInCodeSection); err != nil {
Expand Down Expand Up @@ -449,10 +455,11 @@ operatorSwitch:

// Create a new frame -- entering this block.
frame := controlFrame{
frameID: c.nextFrameID(),
originalStackLenWithoutParam: len(c.stack) - len(bt.Params),
kind: controlFrameKindBlockWithoutContinuationLabel,
blockType: bt,
frameID: c.nextFrameID(),
originalStackLenWithoutParam: len(c.stack) - len(bt.Params),
originalStackLenWithoutParamUint64: c.stackLenInUint64 - bt.ParamNumInUint64,
kind: controlFrameKindBlockWithoutContinuationLabel,
blockType: bt,
}
c.controlFrames.push(frame)

Expand All @@ -473,10 +480,11 @@ operatorSwitch:

// Create a new frame -- entering loop.
frame := controlFrame{
frameID: c.nextFrameID(),
originalStackLenWithoutParam: len(c.stack) - len(bt.Params),
kind: controlFrameKindLoop,
blockType: bt,
frameID: c.nextFrameID(),
originalStackLenWithoutParam: len(c.stack) - len(bt.Params),
originalStackLenWithoutParamUint64: c.stackLenInUint64 - bt.ParamNumInUint64,
kind: controlFrameKindLoop,
blockType: bt,
}
c.controlFrames.push(frame)

Expand Down Expand Up @@ -515,8 +523,9 @@ operatorSwitch:

// Create a new frame -- entering if.
frame := controlFrame{
frameID: c.nextFrameID(),
originalStackLenWithoutParam: len(c.stack) - len(bt.Params),
frameID: c.nextFrameID(),
originalStackLenWithoutParam: len(c.stack) - len(bt.Params),
originalStackLenWithoutParamUint64: c.stackLenInUint64 - bt.ParamNumInUint64,
// Note this will be set to controlFrameKindIfWithElse
// when else opcode found later.
kind: controlFrameKindIfWithoutElse,
Expand All @@ -543,7 +552,7 @@ operatorSwitch:
// If it is currently in unreachable, and the non-nested if,
// reset the stack so we can correctly handle the else block.
top := c.controlFrames.top()
c.stack = c.stack[:top.originalStackLenWithoutParam]
c.stackSwitchAt(top)
top.kind = controlFrameKindIfWithElse

// Re-push the parameters to the if block so that else block can use them.
Expand Down Expand Up @@ -572,7 +581,7 @@ operatorSwitch:

// Reset the stack manipulated by the then block, and re-push the block param types to the stack.

c.stack = c.stack[:frame.originalStackLenWithoutParam]
c.stackSwitchAt(frame)
for _, t := range frame.blockType.Params {
c.stackPush(wasmValueTypeTounsignedType(t))
}
Expand Down Expand Up @@ -601,7 +610,7 @@ operatorSwitch:
return nil
}

c.stack = c.stack[:frame.originalStackLenWithoutParam]
c.stackSwitchAt(frame)
for _, t := range frame.blockType.Results {
c.stackPush(wasmValueTypeTounsignedType(t))
}
Expand All @@ -628,7 +637,7 @@ operatorSwitch:
// We need to reset the stack so that
// the values pushed inside the block.
dropOp := newOperationDrop(c.getFrameDropRange(frame, true))
c.stack = c.stack[:frame.originalStackLenWithoutParam]
c.stackSwitchAt(frame)

// Push the result types onto the stack.
for _, t := range frame.blockType.Results {
Expand Down Expand Up @@ -3505,18 +3514,25 @@ func (c *compiler) stackPeek() (ret unsignedType) {
return
}

func (c *compiler) stackSwitchAt(frame *controlFrame) {
c.stack = c.stack[:frame.originalStackLenWithoutParam]
c.stackLenInUint64 = frame.originalStackLenWithoutParamUint64
}

func (c *compiler) stackPop() (ret unsignedType) {
// No need to check stack bound
// as we can assume that all the operations
// are valid thanks to validateFunction
// at module validation phase.
ret = c.stack[len(c.stack)-1]
c.stack = c.stack[:len(c.stack)-1]
c.stackLenInUint64 -= 1 + int(unsignedTypeV128&ret>>2)
return
}

func (c *compiler) stackPush(ts unsignedType) {
c.stack = append(c.stack, ts)
c.stackLenInUint64 += 1 + int(unsignedTypeV128&ts>>2)
}

// emit adds the operations into the result.
Expand Down Expand Up @@ -3565,7 +3581,7 @@ func (c *compiler) emitDefaultValue(t wasm.ValueType) {
// of the n-th local.
func (c *compiler) localDepth(index wasm.Index) int {
height := c.localIndexToStackHeightInUint64[index]
return c.stackLenInUint64(len(c.stack)) - 1 - int(height)
return c.stackLenInUint64 - 1 - height
}

func (c *compiler) localType(index wasm.Index) (t wasm.ValueType) {
Expand All @@ -3592,32 +3608,14 @@ func (c *compiler) getFrameDropRange(frame *controlFrame, isEnd bool) inclusiveR
} else {
start = frame.blockType.ResultNumInUint64
}
var end int
if frame.kind == controlFrameKindFunction {
// On the function return, we eliminate all the contents on the stack
// including locals (existing below of frame.originalStackLen)
end = c.stackLenInUint64(len(c.stack)) - 1
} else {
end = c.stackLenInUint64(len(c.stack)) - 1 - c.stackLenInUint64(frame.originalStackLenWithoutParam)
}
end := c.stackLenInUint64 - 1 - frame.originalStackLenWithoutParamUint64
if start <= end {
return inclusiveRange{Start: int32(start), End: int32(end)}
} else {
return nopinclusiveRange
}
}

func (c *compiler) stackLenInUint64(ceil int) (ret int) {
for i := 0; i < ceil; i++ {
if c.stack[i] == unsignedTypeV128 {
ret += 2
} else {
ret++
}
}
return
}

func (c *compiler) readMemoryArg(tag string) (memoryArg, error) {
c.result.UsesMemory = true
alignment, num, err := leb128.LoadUint32(c.body[c.pc+1:])
Expand Down
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