1 files changed, 14 insertions, 0 deletions
diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 69e7d25..4e28892 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -760,6 +760,20 @@ ModRefInfo BasicAAResult::getModRefInfo(ImmutableCallSite CS,
       return MRI_NoModRef;
   }
 
+  // If the CallSite is to malloc or calloc, we can assume that it doesn't
+  // modify any IR visible value.  This is only valid because we assume these
+  // routines do not read values visible in the IR.  TODO: Consider special
+  // casing realloc and strdup routines which access only their arguments as
+  // well.  Or alternatively, replace all of this with inaccessiblememonly once
+  // that's implemented fully. 
+  auto *Inst = CS.getInstruction();
+  if (isMallocLikeFn(Inst, &TLI) || isCallocLikeFn(Inst, &TLI)) {
+    // Be conservative if the accessed pointer may alias the allocation -
+    // fallback to the generic handling below.
+    if (getBestAAResults().alias(MemoryLocation(Inst), Loc) == NoAlias)
+      return MRI_NoModRef;
+  }
+
   // While the assume intrinsic is marked as arbitrarily writing so that
   // proper control dependencies will be maintained, it never aliases any
   // particular memory location.