llvm.noalias - SCEV can look through it

[hfinkel]

Summary

This is part of the series started by D9375, and teaches ScalarEvolution to look through the intrinsic. This is necessary, for example, so that loop vectorization can proceed even with llvm.noalias intrinsics inside the loop.

While, in theory, this could lead to rewriting which removes the intrinsics, I think this is unlikely in practice except very late in the pipeline (by LoopVectorize, LSR, etc.), and we can deal with these passes specifically if that turns out to be a problem.

[reames]

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

[hfinkel]

Rebased (and removed an unintentional whitespace change).

[majnemer]

LGTM

lib/Analysis/ScalarEvolution.cpp

5233 ↗

(On Diff #63349)

const auto *II.

llvm/trunk/lib/Analysis/ScalarEvolution.cpp

const SCEV *ScalarEvolution::createSCEV(Value *V) {
   case Instruction::Select:
     // U can also be a select constant expr, which let fall through.  Since
     // createNodeForSelect only works for a condition that is an `ICmpInst`, and
     // constant expressions cannot have instructions as operands, we'd have
     // returned getUnknown for a select constant expressions anyway.
     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/trunk/test/Analysis/ScalarEvolution/returned.ll

+; 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
+