From 63f970ee2484d39782cb9686fdeca00d55e866ca Mon Sep 17 00:00:00 2001 From: Rong Xu Date: Wed, 10 Aug 2016 17:49:11 +0000 Subject: [PATCH] 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 llvm-svn: 278250 --- llvm/lib/Transforms/Utils/LCSSA.cpp | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/llvm/lib/Transforms/Utils/LCSSA.cpp b/llvm/lib/Transforms/Utils/LCSSA.cpp index 8071df6..d15c15a 100644 --- a/llvm/lib/Transforms/Utils/LCSSA.cpp +++ b/llvm/lib/Transforms/Utils/LCSSA.cpp @@ -186,14 +186,14 @@ bool llvm::formLCSSAForInstructions(SmallVectorImpl &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 -- 2.7.4