From 3579e44bf33ed34f8b498834bfb40e407082bf31 Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Tue, 9 Dec 2008 19:47:40 +0000 Subject: [PATCH] Fix a fixme: allow memdep to see past read-only calls when doing load dependence queries. This allows GVN to eliminate a few more instructions on 403.gcc: 152598 gvn - Number of instructions deleted 49240 gvn - Number of loads deleted after: 153986 gvn - Number of instructions deleted 50069 gvn - Number of loads deleted git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60786 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Analysis/MemoryDependenceAnalysis.cpp | 17 +++++++++++++---- 1 file changed, 13 insertions(+), 4 deletions(-) diff --git a/lib/Analysis/MemoryDependenceAnalysis.cpp b/lib/Analysis/MemoryDependenceAnalysis.cpp index cd63c0fc52c..9fcbd8dbf05 100644 --- a/lib/Analysis/MemoryDependenceAnalysis.cpp +++ b/lib/Analysis/MemoryDependenceAnalysis.cpp @@ -213,11 +213,20 @@ getPointerDependencyFrom(Value *MemPtr, uint64_t MemSize, bool isLoad, // See if this instruction (e.g. a call or vaarg) mod/ref's the pointer. // FIXME: If this is a load, we should ignore readonly calls! - if (AA->getModRefInfo(Inst, MemPtr, MemSize) == AliasAnalysis::NoModRef) + switch (AA->getModRefInfo(Inst, MemPtr, MemSize)) { + case AliasAnalysis::NoModRef: + // If the call has no effect on the queried pointer, just ignore it. continue; - - // Otherwise, there is a dependence. - return MemDepResult::getClobber(Inst); + case AliasAnalysis::Ref: + // If the call is known to never store to the pointer, and if this is a + // load query, we can safely ignore it (scan past it). + if (isLoad) + continue; + // FALL THROUGH. + default: + // Otherwise, there is a potential dependence. Return a clobber. + return MemDepResult::getClobber(Inst); + } } // No dependence found. If this is the entry block of the function, it is a