[CaptureTracking] Allow null to be in either icmp operand

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

1 files changed, 7 insertions, 5 deletions

diff --git a/llvm/lib/Analysis/CaptureTracking.cpp b/llvm/lib/Analysis/CaptureTracking.cpp
index f12e50e6c92..fe551bdfe18 100644
--- a/llvm/lib/Analysis/CaptureTracking.cpp
+++ b/llvm/lib/Analysis/CaptureTracking.cpp
@@ -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