[PATCH] llvm.noalias - computeKnownBits should look through them

[hfinkel at anl.gov]

Hi chandlerc, reames,

This is part of the series started by D9375, and teaches computeKnownBits to look through calls to llvm.noalias. This is necessary for pointer-alignment propagation to work.

http://reviews.llvm.org/D9397

Files:
  lib/Analysis/ValueTracking.cpp
  test/Transforms/InstCombine/align-attr.ll

Index: lib/Analysis/ValueTracking.cpp
===================================================================
--- lib/Analysis/ValueTracking.cpp
+++ lib/Analysis/ValueTracking.cpp
@@ -1460,6 +1460,9 @@
     if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
       switch (II->getIntrinsicID()) {
       default: break;
+      case Intrinsic::noalias:
+        computeKnownBits(I->getOperand(0), KnownZero, KnownOne, DL, Depth + 1, Q);
+        break;
       case Intrinsic::ctlz:
       case Intrinsic::cttz: {
         unsigned LowBits = Log2_32(BitWidth)+1;
Index: test/Transforms/InstCombine/align-attr.ll
===================================================================
--- test/Transforms/InstCombine/align-attr.ll
+++ test/Transforms/InstCombine/align-attr.ll
@@ -13,3 +13,19 @@
 ; CHECK: ret i32
 }
 
+define i32 @foo2(i32* align 32 %a) #0 {
+entry:
+  %v = call i32* @llvm.noalias.p0i32(i32* %a, metadata !1)
+  %0 = load i32, i32* %v, align 4
+  ret i32 %0
+
+; CHECK-LABEL: @foo2
+; CHECK-DAG: load i32, i32* %v, align 32
+; CHECK: ret i32
+}
+
+declare i32* @llvm.noalias.p0i32(i32*, metadata) nounwind
+
+!0 = !{!0, !"some domain"}
+!1 = !{!1, !0, !"some scope"}
+

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