MemorySSA: Revert r269678 and r268068; replace with special casing in MemorySSA.
It turns out that too many passes are relying on alias analysis results
for control dependencies. Until we fix that by introducing a more accurate
modelling of control dependencies, special case assume in MemorySSA instead.
Also introduce tests to ensure we don't regress the FunctionAttrs or LICM
passes.
Differential Revision: http://reviews.llvm.org/D20658
llvm-svn: 270823
diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 6d166da..f1b60c6 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -580,20 +580,11 @@
/// Returns the behavior when calling the given function. For use when the call
/// site is not known.
-/// NOTE: Because of the special case handling of llvm.assume below, the result
-/// of this function may not match similar results derived from function
-/// attributes (e.g. "readnone").
FunctionModRefBehavior BasicAAResult::getModRefBehavior(const Function *F) {
// If the function declares it doesn't access memory, we can't do better.
if (F->doesNotAccessMemory())
return FMRB_DoesNotAccessMemory;
- // While the assume intrinsic is marked as arbitrarily writing so that
- // proper control dependencies will be maintained, it never aliases any
- // actual memory locations.
- if (F->getIntrinsicID() == Intrinsic::assume)
- return FMRB_DoesNotAccessMemory;
-
FunctionModRefBehavior Min = FMRB_UnknownModRefBehavior;
// If the function declares it only reads memory, go with that.
diff --git a/llvm/lib/Transforms/Utils/MemorySSA.cpp b/llvm/lib/Transforms/Utils/MemorySSA.cpp
index b87a6d6..9d8c088 100644
--- a/llvm/lib/Transforms/Utils/MemorySSA.cpp
+++ b/llvm/lib/Transforms/Utils/MemorySSA.cpp
@@ -354,6 +354,14 @@
/// \brief Helper function to create new memory accesses
MemoryUseOrDef *MemorySSA::createNewAccess(Instruction *I) {
+ // The assume intrinsic has a control dependency which we model by claiming
+ // that it writes arbitrarily. Ignore that fake memory dependency here.
+ // FIXME: Replace this special casing with a more accurate modelling of
+ // assume's control dependency.
+ if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
+ if (II->getIntrinsicID() == Intrinsic::assume)
+ return nullptr;
+
// Find out what affect this instruction has on memory.
ModRefInfo ModRef = AA->getModRefInfo(I);
bool Def = bool(ModRef & MRI_Mod);