[llvm] Attributor: Don't rely on use_empty for constants (PR #137218)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm created https://github.com/llvm/llvm-project/pull/137218

This allows inferring noalias on a null argument parameter. This
avoids a non-NFC diff in a future change.

>From c45c927526220f10722010865bb5de71790397e1 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Thu, 24 Apr 2025 19:34:23 +0200
Subject: [PATCH] Attributor: Don't rely on use_empty for constants

This allows inferring noalias on a null argument parameter. This
avoids a non-NFC diff in a future change.
---
 llvm/lib/Transforms/IPO/AttributorAttributes.cpp | 2 +-
 llvm/test/Transforms/Attributor/issue87856.ll    | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/llvm/lib/Transforms/IPO/AttributorAttributes.cpp b/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
index ac56df3823e20..1032dede7cb36 100644
--- a/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
+++ b/llvm/lib/Transforms/IPO/AttributorAttributes.cpp
@@ -5746,7 +5746,7 @@ bool AANoCapture::isImpliedByIR(Attributor &A, const IRPosition &IRP,
   assert(ImpliedAttributeKind == Attribute::Captures &&
          "Unexpected attribute kind");
   Value &V = IRP.getAssociatedValue();
-  if (!IRP.isArgumentPosition())
+  if (!isa<Constant>(V) && !IRP.isArgumentPosition())
     return V.use_empty();
 
   // You cannot "capture" null in the default address space.
diff --git a/llvm/test/Transforms/Attributor/issue87856.ll b/llvm/test/Transforms/Attributor/issue87856.ll
index 4990ef909dfaa..592ec33a31369 100644
--- a/llvm/test/Transforms/Attributor/issue87856.ll
+++ b/llvm/test/Transforms/Attributor/issue87856.ll
@@ -4,7 +4,7 @@
 define void @null_ptr_is_valid_call_with_null() #0 {
 ; CHECK-LABEL: define void @null_ptr_is_valid_call_with_null(
 ; CHECK-SAME: ) #[[ATTR0:[0-9]+]] {
-; CHECK-NEXT:    call void @store_as0(ptr nofree noundef writeonly null) #[[ATTR4:[0-9]+]]
+; CHECK-NEXT:    call void @store_as0(ptr noalias nofree noundef writeonly null) #[[ATTR4:[0-9]+]]
 ; CHECK-NEXT:    ret void
 ;
   call void @store_as0(ptr null)