Pointer-comparison folding should look through returned-argument functions

For functions which are known to return a specific argument, pointer-comparison
folding can look through the function calls as part of its analysis.

Differential Revision: http://reviews.llvm.org/D9387

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@275039 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 35 insertions, 0 deletions

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index a41be07fcd5..27c10ee7cf8 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -621,6 +621,11 @@ static Constant *stripAndComputeConstantOffsets(const DataLayout &DL, Value *&V,
         break;
       V = GA->getAliasee();
     } else {
+      if (auto CS = CallSite(V))
+        if (Value *RV = CS.getReturnedArgOperand()) {
+          V = RV;
+          continue;
+        }
       break;
     }
     assert(V->getType()->getScalarType()->isPointerTy() &&
diff --git a/test/Transforms/InstSimplify/returned.ll b/test/Transforms/InstSimplify/returned.ll
new file mode 100644
index 00000000000..0e89e91085d
--- /dev/null
+++ b/test/Transforms/InstSimplify/returned.ll
@@ -0,0 +1,30 @@
+; 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
+