[llvm-commits] [llvm] r60786 - /llvm/trunk/lib/Analysis/MemoryDependenceAnalysis.cpp
Chris Lattner
sabre at nondot.org
Tue Dec 9 11:47:40 PST 2008
Author: lattner
Date: Tue Dec 9 13:47:40 2008
New Revision: 60786
URL: http://llvm.org/viewvc/llvm-project?rev=60786&view=rev
Log:
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
Modified:
llvm/trunk/lib/Analysis/MemoryDependenceAnalysis.cpp
Modified: llvm/trunk/lib/Analysis/MemoryDependenceAnalysis.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/MemoryDependenceAnalysis.cpp?rev=60786&r1=60785&r2=60786&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/MemoryDependenceAnalysis.cpp (original)
+++ llvm/trunk/lib/Analysis/MemoryDependenceAnalysis.cpp Tue Dec 9 13:47:40 2008
@@ -213,11 +213,20 @@
// 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
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