[PATCH] D66321: [CaptureTracking] Allow null to be in either icmp operand

[Johannes Doerfert via Phabricator via llvm-commits]

jdoerfert created this revision.
jdoerfert added reviewers: sanjoy, hfinkel, aykevl, sstefan1, uenoku.
Herald added subscribers: bollu, hiraditya.
Herald added a project: LLVM.

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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D66321

Files:
  llvm/lib/Analysis/CaptureTracking.cpp
  llvm/test/Transforms/FunctionAttrs/nocapture.ll


Index: llvm/test/Transforms/FunctionAttrs/nocapture.ll
===================================================================
--- llvm/test/Transforms/FunctionAttrs/nocapture.ll
+++ llvm/test/Transforms/FunctionAttrs/nocapture.ll
@@ -259,6 +259,12 @@
   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 @@
   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*
Index: llvm/lib/Analysis/CaptureTracking.cpp
===================================================================
--- llvm/lib/Analysis/CaptureTracking.cpp
+++ llvm/lib/Analysis/CaptureTracking.cpp
@@ -331,7 +331,9 @@
       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 @@
           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 @@
           // 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


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