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[CaptureTracking] Allow null to be in either icmp operand

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Summary:
Before we required the comparison against null to be "canonical", hence
null to be operand #1. This patch allows null to be in either operand,
similar to the handling of loaded globals that follows.

Reviewers: sanjoy, hfinkel, aykevl, sstefan1, uenoku

Subscribers: hiraditya, bollu, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66321

llvm-svn: 369158
This commit is contained in:
Johannes Doerfert 2019-08-16 21:53:49 +00:00
parent 25d065f267
commit aad9f9ab3e
2 changed files with 21 additions and 5 deletions
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12
lib/Analysis/CaptureTracking.cpp
View File

@ -331,7 +331,9 @@ void llvm::PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker,
AddUses(I);
break;
case Instruction::ICmp: {
if (auto *CPN = dyn_cast<ConstantPointerNull>(I->getOperand(1))) {
unsigned Idx = (I->getOperand(0) == V) ? 0 : 1;
unsigned OtherIdx = 1 - Idx;
if (auto *CPN = dyn_cast<ConstantPointerNull>(I->getOperand(OtherIdx))) {
// Don't count comparisons of a no-alias return value against null as
// captures. This allows us to ignore comparisons of malloc results
// with null, for example.
@ -339,7 +341,7 @@ void llvm::PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker,
if (isNoAliasCall(V->stripPointerCasts()))
break;
if (!I->getFunction()->nullPointerIsDefined()) {
auto *O = I->getOperand(0)->stripPointerCastsSameRepresentation();
auto *O = I->getOperand(Idx)->stripPointerCastsSameRepresentation();
// An inbounds GEP can either be a valid pointer (pointing into
// or to the end of an allocation), or be null in the default
// address space. So for an inbounds GEPs there is no way to let
@ -353,15 +355,15 @@ void llvm::PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker,
// cannot lead to pointer escapes, because if it is not null it
// must be a valid (in-bounds) pointer.
bool CanBeNull;
if (O->getPointerDereferenceableBytes(I->getModule()->getDataLayout(), CanBeNull))
if (O->getPointerDereferenceableBytes(I->getModule()->getDataLayout(),
CanBeNull))
break;
}
}
// Comparison against value stored in global variable. Given the pointer
// does not escape, its value cannot be guessed and stored separately in a
// global variable.
unsigned OtherIndex = (I->getOperand(0) == V) ? 1 : 0;
auto *LI = dyn_cast<LoadInst>(I->getOperand(OtherIndex));
auto *LI = dyn_cast<LoadInst>(I->getOperand(OtherIdx));
if (LI && isa<GlobalVariable>(LI->getPointerOperand()))
break;
// Otherwise, be conservative. There are crazy ways to capture pointers

14
test/Transforms/FunctionAttrs/nocapture.ll
View File

@ -259,6 +259,12 @@ define i1 @captureICmp(i32* %x) {
ret i1 %1
}
; CHECK: define i1 @captureICmpRev(i32* readnone %x)
define i1 @captureICmpRev(i32* %x) {
%1 = icmp eq i32* null, %x
ret i1 %1
}
; CHECK: define i1 @nocaptureInboundsGEPICmp(i32* nocapture readnone %x)
define i1 @nocaptureInboundsGEPICmp(i32* %x) {
%1 = getelementptr inbounds i32, i32* %x, i32 5
@ -267,6 +273,14 @@ define i1 @nocaptureInboundsGEPICmp(i32* %x) {
ret i1 %3
}
; CHECK: define i1 @nocaptureInboundsGEPICmpRev(i32* nocapture readnone %x)
define i1 @nocaptureInboundsGEPICmpRev(i32* %x) {
%1 = getelementptr inbounds i32, i32* %x, i32 5
%2 = bitcast i32* %1 to i8*
%3 = icmp eq i8* null, %2
ret i1 %3
}
; CHECK: define i1 @nocaptureDereferenceableOrNullICmp(i32* nocapture readnone dereferenceable_or_null(4) %x)
define i1 @nocaptureDereferenceableOrNullICmp(i32* dereferenceable_or_null(4) %x) {
%1 = bitcast i32* %x to i8*