llvm.noalias - Pointer comparison folding should look through them

[hfinkel]

Summary

This is part of the series started by D9375, and makes sure that pointer comparison folding that look though calls to llvm.noalias.

[reames]

This patch appears to either be missing pieces, or I'm not aware of a dependency.

[reames]

Resigning as a reviewer to get a very stale review off my list of blocking tasks in phabricator. Please reopen when desired.

[hfinkel]

Rebased.

[majnemer]

LGTM

llvm/trunk/lib/Analysis/InstructionSimplify.cpp

if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
       V = GEP->getPointerOperand();
     } else if (Operator::getOpcode(V) == Instruction::BitCast) {
       V = cast<Operator>(V)->getOperand(0);
     } else if (GlobalAlias *GA = dyn_cast<GlobalAlias>(V)) {
       if (GA->isInterposable())
         break;
       V = GA->getAliasee();
     } else {
+      if (auto CS = CallSite(V))
+        if (Value *RV = CS.getReturnedArgOperand()) {
+          V = RV;
+          continue;
+        }
       break;
     }
     assert(V->getType()->getScalarType()->isPointerTy() &&
            "Unexpected operand type!");
   } while (Visited.insert(V).second);
 
   Constant *OffsetIntPtr = ConstantInt::get(IntPtrTy, Offset);
   if (V->getType()->isVectorTy())

llvm/trunk/test/Transforms/InstSimplify/returned.ll

+; RUN: opt -instsimplify -S < %s | FileCheck %s
+
+define i1 @bitcast() {
+; CHECK-LABEL: @bitcast(
+  %a = alloca i32
+  %b = alloca i64
+  %x = bitcast i32* %a to i8*
+  %z = bitcast i64* %b to i8*
+  %y = call i8* @func1(i8* %z)
+  %cmp = icmp eq i8* %x, %y
+  ret i1 %cmp
+; CHECK-NEXT: ret i1 false
+}
+
+%gept = type { i32, i32 }
+
+define i1 @gep3() {
+; CHECK-LABEL: @gep3(
+  %x = alloca %gept, align 8
+  %a = getelementptr %gept, %gept* %x, i64 0, i32 0
+  %y = call %gept* @func2(%gept* %x)
+  %b = getelementptr %gept, %gept* %y, i64 0, i32 1
+  %equal = icmp eq i32* %a, %b
+  ret i1 %equal
+; CHECK-NEXT: ret i1 false
+}
+
+declare i8* @func1(i8* returned) nounwind readnone
+declare %gept* @func2(%gept* returned) nounwind readnone
+