Revert "[BasicAliasAnalysis] Remove isMallocOrCallocLikeFn"

This reverts commit 1f2cfc4fdc1eefb2c5f562c77a5fe7e916bbf670.

1 files changed, 14 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index 9485565..fa9ccb0 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -996,6 +996,20 @@ ModRefInfo BasicAAResult::getModRefInfo(const CallBase *Call,
     }
   }
 
+  // If the call is malloc/calloc like, 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.
+  if (isMallocOrCallocLikeFn(Call, &TLI)) {
+    // Be conservative if the accessed pointer may alias the allocation -
+    // fallback to the generic handling below.
+    if (getBestAAResults().alias(MemoryLocation::getBeforeOrAfter(Call), Loc,
+                                 AAQI) == AliasResult::NoAlias)
+      return ModRefInfo::NoModRef;
+  }
+
   // The semantics of memcpy intrinsics either exactly overlap or do not
   // overlap, i.e., source and destination of any given memcpy are either
   // no-alias or must-alias.