Teach SCEV to look through returned-argument functions

When building SCEVs, if a function is known to return its argument, then we can
build the SCEV using the corresponding argument value.

Differential Revision: http://reviews.llvm.org/D9381

llvm-svn: 275037

llvm/lib/Analysis/ScalarEvolution.cpp

@@ -5225,6 +5225,13 @@ const SCEV *ScalarEvolution::createSCEV(Value *V) {
     if (isa<Instruction>(U))
       return createNodeForSelectOrPHI(cast<Instruction>(U), U->getOperand(0),
                                       U->getOperand(1), U->getOperand(2));
+    break;
+
+  case Instruction::Call:
+  case Instruction::Invoke:
+    if (Value *RV = CallSite(U).getReturnedArgOperand())
+      return getSCEV(RV);
+    break;
   }
 
   return getUnknown(V);

llvm/test/Analysis/ScalarEvolution/returned.ll

@@ -0,0 +1,16 @@
+; RUN: opt < %s -S -analyze -scalar-evolution | FileCheck %s
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
+
+define i8* @foo(i32 %no, i8* nocapture %d) nounwind {
+entry:
+  %v = call i8* @func1(i8* %d)
+  %w = getelementptr i8, i8* %v, i64 5
+  ret i8* %w
+}
+
+; CHECK-LABEL: Classifying expressions for: @foo
+; CHECK: %w = getelementptr i8, i8* %v, i64 5
+; CHECK-NEXT: (5 + %d)
+
+declare i8* @func1(i8* returned) nounwind argmemonly
+