add getUnderlyingObjectSize()

this is similar to getObjectSize(), but doesnt subtract the offset
tweak the BasicAA code accordingly (per PR14988)

llvm-svn: 176407

1 files changed, 1 insertions, 30 deletions

diff --git a/llvm/lib/Analysis/BasicAliasAnalysis.cpp b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
index ad36cbbec3a..4139336f268 100644
--- a/llvm/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/BasicAliasAnalysis.cpp
@@ -88,7 +88,7 @@ static uint64_t getObjectSize(const Value *V, const DataLayout &TD,
                               const TargetLibraryInfo &TLI,
                               bool RoundToAlign = false) {
   uint64_t Size;
-  if (getObjectSize(V, Size, &TD, &TLI, RoundToAlign))
+  if (getUnderlyingObjectSize(V, Size, &TD, &TLI, RoundToAlign))
     return Size;
   return AliasAnalysis::UnknownSize;
 }
@@ -98,35 +98,6 @@ static uint64_t getObjectSize(const Value *V, const DataLayout &TD,
 static bool isObjectSmallerThan(const Value *V, uint64_t Size,
                                 const DataLayout &TD,
                                 const TargetLibraryInfo &TLI) {
-  // Note that the meanings of the "object" are slightly different in the
-  // following contexts:
-  //    c1: llvm::getObjectSize()
-  //    c2: llvm.objectsize() intrinsic
-  //    c3: isObjectSmallerThan()
-  // c1 and c2 share the same meaning; however, the meaning of "object" in c3
-  // refers to the "entire object".
-  //
-  //  Consider this example:
-  //     char *p = (char*)malloc(100)
-  //     char *q = p+80;
-  //
-  //  In the context of c1 and c2, the "object" pointed by q refers to the
-  // stretch of memory of q[0:19]. So, getObjectSize(q) should return 20.
-  //
-  //  However, in the context of c3, the "object" refers to the chunk of memory
-  // being allocated. So, the "object" has 100 bytes, and q points to the middle
-  // the "object". In case q is passed to isObjectSmallerThan() as the 1st
-  // parameter, before the llvm::getObjectSize() is called to get the size of
-  // entire object, we should:
-  //    - either rewind the pointer q to the base-address of the object in
-  //      question (in this case rewind to p), or
-  //    - just give up. It is up to caller to make sure the pointer is pointing
-  //      to the base address the object.
-  // 
-  // We go for 2nd option for simplicity.
-  if (!isIdentifiedObject(V))
-    return false;
-
   // This function needs to use the aligned object size because we allow
   // reads a bit past the end given sufficient alignment.
   uint64_t ObjectSize = getObjectSize(V, TD, TLI, /*RoundToAlign*/true);