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Fix LCSSA increased compile time

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We are seeing r276077 drastically increasing compiler time for our larger
benchmarks in PGO profile generation build (both clang based and IR based
mode) -- it can be 20x slower than without the patch (like from 30 secs to
780 secs)

The increased time are all in pass LCSSA. The problematic code is about
PostProcessPHIs after use-rewrite. Note that the InsertedPhis from ssa_updater
is accumulating (never been cleared). Since the inserted PHIs are added to the
candidate for each rewrite, The earlier ones will be repeatedly added. Later
when adding the new PHIs to the work-list, we don't check the duplication
either. This can result in extremely long work-list that containing tons of
duplicated PHIs.

This patch fixes the issue by hoisting the code out of the loop.

Differential Revision: http://reviews.llvm.org/D23344


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278250 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rong Xu 2016-08-10 17:49:11 +00:00
parent c047ae7294
commit 9a1106c09e
1 changed files with 7 additions and 7 deletions
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14
lib/Transforms/Utils/LCSSA.cpp
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@ -186,14 +186,14 @@ bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
// Otherwise, do full PHI insertion.
SSAUpdate.RewriteUse(*UseToRewrite);
}
// SSAUpdater might have inserted phi-nodes inside other loops. We'll need
// to post-process them to keep LCSSA form.
for (PHINode *InsertedPN : InsertedPHIs) {
if (auto *OtherLoop = LI.getLoopFor(InsertedPN->getParent()))
if (!L->contains(OtherLoop))
PostProcessPHIs.push_back(InsertedPN);
}
// SSAUpdater might have inserted phi-nodes inside other loops. We'll need
// to post-process them to keep LCSSA form.
for (PHINode *InsertedPN : InsertedPHIs) {
if (auto *OtherLoop = LI.getLoopFor(InsertedPN->getParent()))
if (!L->contains(OtherLoop))
PostProcessPHIs.push_back(InsertedPN);
}
// Post process PHI instructions that were inserted into another disjoint