[PATCH] D68492: [PATCH 09/38] [noalias] D9376: llvm.noalias - handling of dead intrinsics

[Jeroen Dobbelaere via Phabricator via llvm-commits]

jeroen.dobbelaere created this revision.
jeroen.dobbelaere added reviewers: hfinkel, jdoerfert.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

This is part of the series started by D68484 <https://reviews.llvm.org/D68484>.

Rebase of D9376 <https://reviews.llvm.org/D9376>


https://reviews.llvm.org/D68492

Files:
  llvm/lib/Analysis/InstructionSimplify.cpp
  llvm/lib/Transforms/Utils/Local.cpp
  llvm/test/Transforms/InstSimplify/noalias.ll


Index: llvm/test/Transforms/InstSimplify/noalias.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/InstSimplify/noalias.ll
@@ -0,0 +1,33 @@
+; RUN: opt -instsimplify -S < %s | FileCheck %s
+
+define void @test1(i8* %ptr) {
+  call i8* @llvm.noalias.p0i8(i8* %ptr, metadata !1)
+  ret void
+
+; CHECK-LABEL: @test1
+; CHECK-NOT: llvm.noalias.p0i8
+; CHECK: ret void
+}
+
+define i8* @test2a() {
+  %v = call i8* @llvm.noalias.p0i8(i8* null, metadata !1)
+  ret i8* %v
+
+; CHECK-LABEL: @test2a
+; CHECK-NOT: llvm.noalias.p0i8
+; CHECK: ret i8* null
+}
+
+define i8* @test2() {
+  %v = call i8* @llvm.noalias.p0i8(i8* undef, metadata !1)
+  ret i8* %v
+
+; CHECK-LABEL: @test2
+; CHECK-NOT: llvm.noalias.p0i8
+; CHECK: ret i8* undef
+}
+
+declare i8* @llvm.noalias.p0i8(i8*, metadata) nounwind
+
+!0 = !{!0, !"some domain"}
+!1 = !{!1, !0, !"some scope"}
Index: llvm/lib/Transforms/Utils/Local.cpp
===================================================================
--- llvm/lib/Transforms/Utils/Local.cpp
+++ llvm/lib/Transforms/Utils/Local.cpp
@@ -417,6 +417,12 @@
 
       return false;
     }
+
+    // noalias intrinsics are dead if they have no uses (they're tagged as
+    // writing, but that is only to maintain control dependencies, not because
+    // they actually write anything).
+    if (II->getIntrinsicID() == Intrinsic::noalias)
+      return II->use_empty();
   }
 
   if (isAllocLikeFn(I, TLI))
Index: llvm/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/lib/Analysis/InstructionSimplify.cpp
+++ llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5146,6 +5146,18 @@
 
   Function *F = cast<Function>(Call->getCalledFunction());
   Intrinsic::ID IID = F->getIntrinsicID();
+
+  // We can remove a noalias intrinsic if the pointer value is undef (by
+  // forwarding the undef). The same goes for an address-space-zero null
+  // pointer.
+  if (IID == Intrinsic::noalias) {
+    Value *Arg0 = Call->getArgOperand(0);
+    if (isa<UndefValue>(Arg0) ||
+        (isa<ConstantPointerNull>(Arg0) &&
+         Arg0->getType()->getPointerAddressSpace() == 0))
+      return Arg0;
+  }
+
   if (NumOperands == 1)
     return simplifyUnaryIntrinsic(F, Call->getArgOperand(0), Q);
 


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