[llvm] r278250 - Fix LCSSA increased compile time
Rong Xu via llvm-commits
llvm-commits at lists.llvm.org
Wed Aug 10 10:49:12 PDT 2016
Author: xur
Date: Wed Aug 10 12:49:11 2016
New Revision: 278250
URL: http://llvm.org/viewvc/llvm-project?rev=278250&view=rev
Log:
Fix LCSSA increased compile time
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
Modified:
llvm/trunk/lib/Transforms/Utils/LCSSA.cpp
Modified: llvm/trunk/lib/Transforms/Utils/LCSSA.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/LCSSA.cpp?rev=278250&r1=278249&r2=278250&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/LCSSA.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/LCSSA.cpp Wed Aug 10 12:49:11 2016
@@ -186,14 +186,14 @@ bool llvm::formLCSSAForInstructions(Smal
// 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
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