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[LICM] Compute exit blocks for promotion eagerly. NFC. 

This moves the exit block and insertion point computation to be eager,
instead of after seeing the first scalar we can promote.

The cost is relatively small (the computation happens anyway, see discussion
on D28147), and the code is easier to follow, and can bail out earlier
if there's a catchswitch present.

llvm-svn: 290729
This commit is contained in:
Michael Kuperstein 2016-12-29 23:11:19 +00:00
parent 5566092963
commit ff36baefe7
1 changed files with 32 additions and 31 deletions
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41
llvm/lib/Transforms/Scalar/LICM.cpp
View File

@ -256,20 +256,34 @@ bool LoopInvariantCodeMotion::runOnLoop(Loop *L, AliasAnalysis *AA,
// preheader for SSA updater, so also avoid sinking when no preheader
// is available.
if (!DisablePromotion && Preheader && L->hasDedicatedExits()) {
// Figure out the loop exits and their insertion points
SmallVector<BasicBlock *, 8> ExitBlocks;
L->getUniqueExitBlocks(ExitBlocks);
// We can't insert into a catchswitch.
bool HasCatchSwitch = llvm::any_of(ExitBlocks, [](BasicBlock *Exit) {
return isa<CatchSwitchInst>(Exit->getTerminator());
});
if (!HasCatchSwitch) {
SmallVector<Instruction *, 8> InsertPts;
InsertPts.reserve(ExitBlocks.size());
for (BasicBlock *ExitBlock : ExitBlocks)
InsertPts.push_back(&*ExitBlock->getFirstInsertionPt());
PredIteratorCache PIC;
bool Promoted = false;
// Loop over all of the alias sets in the tracker object.
for (AliasSet &AS : *CurAST)
Promoted |= promoteLoopAccessesToScalars(
AS, ExitBlocks, InsertPts, PIC, LI, DT, TLI, L, CurAST, &SafetyInfo);
Promoted |=
promoteLoopAccessesToScalars(AS, ExitBlocks, InsertPts, PIC, LI, DT,
TLI, L, CurAST, &SafetyInfo);
// Once we have promoted values across the loop body we have to recursively
// reform LCSSA as any nested loop may now have values defined within the
// loop used in the outer loop.
// Once we have promoted values across the loop body we have to
// recursively reform LCSSA as any nested loop may now have values defined
// within the loop used in the outer loop.
// FIXME: This is really heavy handed. It would be a bit better to use an
// SSAUpdater strategy during promotion that was LCSSA aware and reformed
// it as it went.
@ -278,6 +292,7 @@ bool LoopInvariantCodeMotion::runOnLoop(Loop *L, AliasAnalysis *AA,
Changed |= Promoted;
}
}
// Check that neither this loop nor its parent have had LCSSA broken. LICM is
// specifically moving instructions across the loop boundary and so it is
@ -1016,24 +1031,10 @@ bool llvm::promoteLoopAccessesToScalars(
PromotionIsLegal =
isAllocLikeFn(Object, TLI) && !PointerMayBeCaptured(Object, true, true);
}
if (!PromotionIsLegal)
return Changed;
// Figure out the loop exits and their insertion points, if this is the
// first promotion.
if (ExitBlocks.empty()) {
CurLoop->getUniqueExitBlocks(ExitBlocks);
InsertPts.clear();
InsertPts.reserve(ExitBlocks.size());
for (BasicBlock *ExitBlock : ExitBlocks)
InsertPts.push_back(&*ExitBlock->getFirstInsertionPt());
}
// Can't insert into a catchswitch.
for (BasicBlock *ExitBlock : ExitBlocks)
if (isa<CatchSwitchInst>(ExitBlock->getTerminator()))
return Changed;
// Otherwise, this is safe to promote, lets do it!
DEBUG(dbgs() << "LICM: Promoting value stored to in loop: " << *SomePtr
<< '\n');