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Bug 1508550 - StackMapGenerator::createStackMap: don't clone the MachineStackTracker. r=lth.

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Currently createStackMap makes a temporary clone of StackMapGenerator::mst_ on
every call.  This will cause a heap allocation and free in the case where
mst_'s vector size exceeds its inline capacity (64 booleans).  This patch
removes the cloning and instead adds a second MachineStackTracker,
augmentedMst_, to StackMapGenerator, which is used as the temporary inside
createStackMap.  The expectation is that augmentedMst_'s vector will grow in
capacity monotonically during the lifetime of the StackMapGenerator, that is,
over multiple calls to createStackMap.  This should significantly cut down on
heap (re)allocation caused by createStackMap.

--HG--
extra : rebase_source : 3a682e88571c1452f15efe711be3e403f64e0a8f
This commit is contained in:
Julian Seward 2018-12-17 08:08:13 +01:00
parent 2887ed4c57
commit 1c2b472ac1
1 changed files with 21 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

29
js/src/wasm/WasmBaselineCompile.cpp
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@ -2043,6 +2043,13 @@ class MachineStackTracker {
MOZ_ASSERT(numPtrs_ <= length());
return numPtrs_;
}
// Discard all contents, but (per mozilla::Vector::clear semantics) don't
// free or reallocate any dynamic storage associated with |vec_|.
void clear() {
vec_.clear();
numPtrs_ = 0;
}
};
// StackMapGenerator, which carries all state needed to create stack maps.
@ -2097,6 +2104,11 @@ struct StackMapGenerator {
// BaseCompiler::stk_.
size_t memRefsOnStk_;
// This is a copy of mst_ that is used only within individual calls to
// createStackMap. It is here only to avoid possible heap allocation costs
// resulting from making it local to createStackMap().
MachineStackTracker augmentedMst_;
StackMapGenerator(StackMaps* stackMaps, const MachineState& trapExitLayout,
const size_t trapExitLayoutNumWords,
const MacroAssembler& masm)
@ -2182,10 +2194,11 @@ struct StackMapGenerator {
}
#endif
// Start with the frame-setup map, and add operand-stack information
// to that.
MachineStackTracker augmentedMst;
if (!mst_.cloneTo(&augmentedMst)) {
// Start with the frame-setup map, and add operand-stack information to
// that. augmentedMst_ holds live data only within individual calls to
// createStackMap.
augmentedMst_.clear();
if (!mst_.cloneTo(&augmentedMst_)) {
return false;
}
@ -2227,7 +2240,7 @@ struct StackMapGenerator {
uint32_t bodyPushedBytes =
framePushedExcludingArgs.value() - framePushedAtEntryToBody_.value();
MOZ_ASSERT(0 == bodyPushedBytes % sizeof(void*));
if (!augmentedMst.pushNonGCPointers(bodyPushedBytes / sizeof(void*))) {
if (!augmentedMst_.pushNonGCPointers(bodyPushedBytes / sizeof(void*))) {
return false;
}
}
@ -2304,13 +2317,13 @@ struct StackMapGenerator {
MOZ_ASSERT(v.offs() <= framePushedExcludingArgs.value());
uint32_t offsFromMapLowest = framePushedExcludingArgs.value() - v.offs();
MOZ_ASSERT(0 == offsFromMapLowest % sizeof(void*));
augmentedMst.setGCPointer(offsFromMapLowest / sizeof(void*));
augmentedMst_.setGCPointer(offsFromMapLowest / sizeof(void*));
}
// Create the final StackMap. The initial map is zeroed out, so there's
// no need to write zero bits in it.
const uint32_t extraWords = extras.length();
const uint32_t augmentedMstWords = augmentedMst.length();
const uint32_t augmentedMstWords = augmentedMst_.length();
const uint32_t numMappedWords = extraWords + augmentedMstWords;
StackMap* stackMap = StackMap::create(numMappedWords);
if (!stackMap) {
@ -2329,7 +2342,7 @@ struct StackMapGenerator {
}
// Followed by the "main" part of the map.
for (uint32_t i = 0; i < augmentedMstWords; i++) {
if (augmentedMst.isGCPointer(i)) {
if (augmentedMst_.isGCPointer(i)) {
stackMap->setBit(numMappedWords - 1 - i);
}
}