Author: resistor
Date: Sun Feb 17 15:29:08 2008
New Revision: 47247
URL: http://llvm.org/viewvc/llvm-project?rev=47247&view=rev
Log:
Teach getModRefInfo that memcpy, memmove, and memset don't "capture" memory
addresses.
Also, noalias arguments are be considered "like" stack allocated ones for this
purpose, because
the only way they can be modref'ed is if they escape somewhere in the current
function.
Modified:
llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
Modified: llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp
URL:
http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp?rev=47247&r1=47246&r2=47247&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp (original)
+++ llvm/trunk/lib/Analysis/BasicAliasAnalysis.cpp Sun Feb 17 15:29:08 2008
@@ -21,7 +21,7 @@
#include "llvm/ParameterAttributes.h"
#include "llvm/GlobalVariable.h"
#include "llvm/Instructions.h"
-#include "llvm/Intrinsics.h"
+#include "llvm/IntrinsicInst.h"
#include "llvm/Pass.h"
#include "llvm/Target/TargetData.h"
#include "llvm/ADT/SmallVector.h"
@@ -228,6 +228,13 @@
// If returned, the address will escape to calling functions, but no
// callees could modify it.
break; // next use
+ case Instruction::Call:
+ // If the call is to a few known safe intrinsics, we know that it does
+ // not escape
+ if (isa<MemIntrinsic>(I))
+ return false;
+ else
+ return true;
default:
return true;
}
@@ -247,8 +254,11 @@
// Allocations and byval arguments are "new" objects.
if (Object &&
(isa<AllocationInst>(Object) ||
- (isa<Argument>(Object) && cast<Argument>(Object)->hasByValAttr()))) {
- // Okay, the pointer is to a stack allocated object. If we can prove
that
+ (isa<Argument>(Object) &&
+ (cast<Argument>(Object)->hasByValAttr() ||
+ cast<Argument>(Object)->hasNoAliasAttr()))))
{
+ // Okay, the pointer is to a stack allocated (or effectively so, for
+ // for noalias parameters) object. If we can prove that
// the pointer never "escapes", then we know the call cannot clobber it,
// because it simply can't get its address.
if (!AddressMightEscape(Object))
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