llvm.noalias - CodeGen support

[hfinkel]

Summary

This is part of the series started by D9375, and adds CodeGen support for llvm.noalias. The support is trivial (the intrinsic always returns its argument).

[reames]

LGTM

[hfinkel]

Rebased.

[majnemer]

LGTM

[hfinkel]

Rebased

[hfinkel]

Rebased.

lib/CodeGen/IntrinsicLowering.cpp

void IntrinsicLowering::LowerIntrinsicCall(CallInst *CI) {
   case Intrinsic::ptr_annotation:
     // Just drop the annotation, but forward the value
     CI->replaceAllUsesWith(CI->getOperand(0));
     break;
 
   case Intrinsic::assume:
   case Intrinsic::var_annotation:
     break;   // Strip out these intrinsics
- 
+  case Intrinsic::noalias:
+    // Just forward the value
+    CI->replaceAllUsesWith(CI->getOperand(0));
+    break;
+ 
   case Intrinsic::memcpy: {
     Type *IntPtr = DL.getIntPtrType(Context);
     Value *Size = Builder.CreateIntCast(CI->getArgOperand(2), IntPtr,
                                         /* isSigned */ false);
     Value *Ops[3];
     Ops[0] = CI->getArgOperand(0);
     Ops[1] = CI->getArgOperand(1);
     Ops[2] = Size;

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

else
       Res = DAG.getConstant(0, sdl, Ty);
 
     setValue(&I, Res);
     return nullptr;
   }
   case Intrinsic::annotation:
   case Intrinsic::ptr_annotation:
   case Intrinsic::invariant_group_barrier:
+  case Intrinsic::noalias:
     // Drop the intrinsic, but forward the value
     setValue(&I, getValue(I.getOperand(0)));
     return nullptr;
   case Intrinsic::assume:
   case Intrinsic::var_annotation:
     // Discard annotate attributes and assumptions
     return nullptr;
 

test/CodeGen/Generic/noalias.ll

+; RUN: llc < %s
+
+define i8* @main(i8* %p) {
+  %v = call i8* @llvm.noalias.p0i8(i8* %p, metadata !1)
+  ret i8* %v
+}
+
+declare i8* @llvm.noalias.p0i8(i8*, metadata) nounwind
+
+!0 = !{!0, !"some domain"}
+!1 = !{!1, !0, !"some scope"}
+