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[CopyPropagation] Eliminate redundant moves.

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SemanticARCOpts already eliminates move values that are redundant that
block its optimizations.  But it's always run after CopyPropagation.

Because move_values divide copy-extended lifetimes, move_values obstruct
lifetime canonicalization.  If a move_value isn't separating lifetimes
with different characteristics (specifically: lexicallity, escaping),
then it is only obstructing lifetime canonicalization.  Remove it
before canonicalizing the lifetime of the moved-from value.
This commit is contained in:
Nate Chandler
2023-03-13 17:07:19 -07:00
parent e9294539f0
commit 16216924b1
4 changed files with 104 additions and 43 deletions
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26
lib/SILOptimizer/Transforms/CopyPropagation.cpp
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@@ -42,6 +42,7 @@
#include "swift/SIL/BasicBlockDatastructures.h"
#include "swift/SIL/BasicBlockUtils.h"
#include "swift/SIL/DebugUtils.h"
#include "swift/SIL/OwnershipUtils.h"
#include "swift/SIL/SILUndef.h"
#include "swift/SILOptimizer/Analysis/BasicCalleeAnalysis.h"
#include "swift/SILOptimizer/Analysis/DeadEndBlocksAnalysis.h"
@@ -263,6 +264,24 @@ static bool convertExtractsToDestructures(CanonicalDefWorklist &copiedDefs,
return changed;
}
//===----------------------------------------------------------------------===//
// MARK: Eliminate redundant moves
//===----------------------------------------------------------------------===//
/// If the specified move_value is redundant (there's no benefit to separating
/// the lifetime at it), replace its uses with uses of the moved-from value and
/// delete it.
static bool eliminateRedundantMove(MoveValueInst *mvi,
InstructionDeleter &deleter) {
if (!isRedundantMoveValue(mvi))
return false;
mvi->replaceAllUsesWith(mvi->getOperand());
// Call InstructionDeleter::forceDeleteWithUsers to avoid "fixing up"
// ownership of the moved-from value, i.e. inserting a destroy_value.
deleter.forceDeleteWithUsers(mvi);
return true;
}
//===----------------------------------------------------------------------===//
// MARK: Sink owned forwarding operations
//===----------------------------------------------------------------------===//
@@ -420,6 +439,7 @@ void CopyPropagation::run() {
bool changed = false;
StackList<BeginBorrowInst *> beginBorrowsToShrink(f);
StackList<MoveValueInst *> moveValues(f);
// Driver: Find all copied or borrowed defs.
for (auto &bb : *f) {
@@ -428,6 +448,8 @@ void CopyPropagation::run() {
defWorklist.updateForCopy(copy);
} else if (auto *borrow = dyn_cast<BeginBorrowInst>(&i)) {
beginBorrowsToShrink.push_back(borrow);
} else if (auto *move = dyn_cast<MoveValueInst>(&i)) {
moveValues.push_back(move);
} else if (canonicalizeAll) {
if (auto *destroy = dyn_cast<DestroyValueInst>(&i)) {
defWorklist.updateForCopy(destroy->getOperand());
@@ -480,9 +502,13 @@ void CopyPropagation::run() {
hoistDestroysOfOwnedLexicalValue(folded, *f, deleter, calleeAnalysis);
// Keep running even if the new move's destroys can't be hoisted.
(void)hoisted;
eliminateRedundantMove(folded, deleter);
firstRun = false;
}
}
for (auto *mvi : moveValues) {
eliminateRedundantMove(mvi, deleter);
}
for (auto *argument : f->getArguments()) {
if (argument->getOwnershipKind() == OwnershipKind::Owned) {
hoistDestroysOfOwnedLexicalValue(argument, *f, deleter, calleeAnalysis);