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Tweak the LICM code to reuse the first sub-loop instead of creating a new one

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LICM starts with an *empty* AST, and then merges in each sub-loop. While the
add code is appropriate for sub-loop 2 and up, it's utterly unnecessary for
sub-loop 1. If the AST starts off empty, we can just clone/move the contents
of the subloop into the containing AST.

Reviewed-by: Philip Reames <listmail@philipreames.com>

Differential Revision: http://reviews.llvm.org/D16753

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@260892 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Roman Gareev 2016-02-15 14:48:50 +00:00
parent 6cde049097
commit 78d3a49fad
1 changed files with 32 additions and 14 deletions
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46
lib/Transforms/Scalar/LICM.cpp
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@ -164,6 +164,11 @@ namespace {
/// Simple Analysis hook. Delete loop L from alias set map.
void deleteAnalysisLoop(Loop *L) override;
/// Returns an owning pointer to an alias set which incorporates aliasing
/// info from all subloops of L, but does not include instructions in L
/// itself.
AliasSetTracker *collectAliasInfoFromSubLoops(Loop *L);
};
}
@ -202,20 +207,7 @@ bool LICM::runOnLoop(Loop *L, LPPassManager &LPM) {
assert(L->isLCSSAForm(*DT) && "Loop is not in LCSSA form.");
CurAST = new AliasSetTracker(*AA);
// Collect Alias info from subloops.
for (Loop *InnerL : L->getSubLoops()) {
AliasSetTracker *InnerAST = LoopToAliasSetMap[InnerL];
assert(InnerAST && "Where is my AST?");
// What if InnerLoop was modified by other passes ?
CurAST->add(*InnerAST);
// Once we've incorporated the inner loop's AST into ours, we don't need the
// subloop's anymore.
delete InnerAST;
LoopToAliasSetMap.erase(InnerL);
}
CurAST = collectAliasInfoFromSubLoops(L);
CurLoop = L;
@ -1065,6 +1057,32 @@ bool llvm::promoteLoopAccessesToScalars(AliasSet &AS,
return Changed;
}
/// Returns an owning pointer to an alias set which incorporates aliasing info
/// from all subloops of L, but does not include instructions in L itself.
///
AliasSetTracker *LICM::collectAliasInfoFromSubLoops(Loop *L) {
AliasSetTracker *CurAST = nullptr;
for (Loop *InnerL : L->getSubLoops()) {
AliasSetTracker *InnerAST = LoopToAliasSetMap[InnerL];
assert(InnerAST && "Where is my AST?");
if (CurAST != nullptr) {
// What if InnerLoop was modified by other passes ?
CurAST->add(*InnerAST);
// Once we've incorporated the inner loop's AST into ours, we don't need
// the subloop's anymore.
delete InnerAST;
} else {
CurAST = InnerAST;
}
LoopToAliasSetMap.erase(InnerL);
}
if (CurAST == nullptr)
CurAST = new AliasSetTracker(*AA);
return CurAST;
}
/// Simple analysis hook. Clone alias set info.
///
void LICM::cloneBasicBlockAnalysis(BasicBlock *From, BasicBlock *To, Loop *L) {