From 8e4df489d0e02e0fbdd00ed829e70e5f21998162 Mon Sep 17 00:00:00 2001 From: Nadav Rotem Date: Tue, 9 Apr 2013 18:16:05 +0000 Subject: Revert r176408 and r176407 to address PR15540. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179111 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Analysis/BasicAliasAnalysis.cpp | 31 ++++++++++++++++++++++++++++++- 1 file changed, 30 insertions(+), 1 deletion(-) (limited to 'lib/Analysis/BasicAliasAnalysis.cpp') diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp index ae6da1af0c..f8509dd070 100644 --- a/lib/Analysis/BasicAliasAnalysis.cpp +++ b/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 (getUnderlyingObjectSize(V, Size, &TD, &TLI, RoundToAlign)) + if (getObjectSize(V, Size, &TD, &TLI, RoundToAlign)) return Size; return AliasAnalysis::UnknownSize; } @@ -98,6 +98,35 @@ 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); -- cgit v1.2.3-18-g5258