From 9971a6841c2df37b57eadc27d7a7ad4440cd8b70 Mon Sep 17 00:00:00 2001 From: James Molloy Date: Thu, 7 Jan 2016 13:33:28 +0000 Subject: [GlobalsAA] Partially back out r248576 See PR25822 for a more full summary, but we were conflating the concepts of "capture" and "escape". We were proving nocapture and using that proof to infer noescape, which is not true. Escaped-ness is a function-local property - as soon as a value is used in a call argument it escapes. Capturedness is a related but distinct property. It implies a *temporally limited* escape. Consider: static int a; int b; int g(int * nocapture arg); int f() { a = 2; // Even though a escapes to g, it is not captured so can be treated as non-escaping here. g(&a); // But here it must be treated as escaping. g(&b); // Now that g(&a) has returned we know it was not captured so we can treat it as non-escaping again. } The original commit did not sufficiently understand this nuance and so caused PR25822 and PR26046. r248576 included both a performance improvement (which has been backed out) and a related conformance fix (which has been kept along with its testcase). llvm-svn: 257058 --- llvm/lib/Analysis/GlobalsModRef.cpp | 15 --------------- 1 file changed, 15 deletions(-) (limited to 'llvm/lib/Analysis') diff --git a/llvm/lib/Analysis/GlobalsModRef.cpp b/llvm/lib/Analysis/GlobalsModRef.cpp index 249f3954d55..1babb822074 100644 --- a/llvm/lib/Analysis/GlobalsModRef.cpp +++ b/llvm/lib/Analysis/GlobalsModRef.cpp @@ -358,21 +358,6 @@ bool GlobalsAAResult::AnalyzeUsesOfPointer(Value *V, if (CS.isArgOperand(&U) && isFreeCall(I, &TLI)) { if (Writers) Writers->insert(CS->getParent()->getParent()); - } else if (CS.doesNotCapture(CS.getDataOperandNo(&U))) { - Function *ParentF = CS->getParent()->getParent(); - // A nocapture argument may be read from or written to, but does not - // escape unless the call can somehow recurse. - // - // nocapture "indicates that the callee does not make any copies of - // the pointer that outlive itself". Therefore if we directly or - // indirectly recurse, we must treat the pointer as escaping. - if (FunctionToSCCMap[ParentF] == - FunctionToSCCMap[CS.getCalledFunction()]) - return true; - if (Readers) - Readers->insert(ParentF); - if (Writers) - Writers->insert(ParentF); } else { return true; // Argument of an unknown call. } -- cgit v1.2.3