[llvm] [GVN] Add test for scoped-alias metadata dropped on coerced loads (PR #206416)

[Madhur Amilkanthwar via llvm-commits]

https://github.com/madhur13490 created https://github.com/llvm/llvm-project/pull/206416

Precommit test capturing current behavior: when GVN forwards a wider
load to a narrower load at an offset, dropUnknownNonDebugMetadata
strips !noalias and !alias.scope from the surviving wider load even
though that load is unchanged and the metadata stays valid.

>From 149d4b4a3665d42b491a17b82cd3a62bf3e55ff9 Mon Sep 17 00:00:00 2001
From: Madhur Amilkanthwar <madhura at nvidia.com>
Date: Sat, 27 Jun 2026 00:03:34 -0700
Subject: [PATCH] [GVN] Add test for scoped-alias metadata dropped on coerced
 loads

Precommit test capturing current behavior: when GVN forwards a wider
load to a narrower load at an offset, dropUnknownNonDebugMetadata
strips !noalias and !alias.scope from the surviving wider load even
though that load is unchanged and the metadata stays valid.
---
 .../Transforms/GVN/rle-coerced-noalias.ll     | 94 +++++++++++++++++++
 1 file changed, 94 insertions(+)
 create mode 100644 llvm/test/Transforms/GVN/rle-coerced-noalias.ll

diff --git a/llvm/test/Transforms/GVN/rle-coerced-noalias.ll b/llvm/test/Transforms/GVN/rle-coerced-noalias.ll
new file mode 100644
index 0000000000000..277e054fdccd5
--- /dev/null
+++ b/llvm/test/Transforms/GVN/rle-coerced-noalias.ll
@@ -0,0 +1,94 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 6
+; RUN: opt -S -passes=gvn < %s | FileCheck %s
+
+; When GVN coerces a wider load into a narrower load at an offset, it strips
+; !noalias and !alias.scope from the surviving wider load. That load is
+; unchanged and still accesses the same memory, so the metadata stays valid
+; and should be kept. It is currently dropped.
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+; The i8 load at P+1 partially aliases the i32 load at P and is coerced from
+; it. The surviving i32 load should keep its !noalias.
+define i32 @noalias_dropped_local(ptr %p) {
+; CHECK-LABEL: define i32 @noalias_dropped_local(
+; CHECK-SAME: ptr [[P:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[WIDE:%.*]] = load i32, ptr [[P]], align 4
+; CHECK-NEXT:    [[P1:%.*]] = getelementptr inbounds i8, ptr [[P]], i64 1
+; CHECK-NEXT:    [[TMP0:%.*]] = lshr i32 [[WIDE]], 8
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc i32 [[TMP0]] to i8
+; CHECK-NEXT:    [[CONV:%.*]] = zext i8 [[TMP1]] to i32
+; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[WIDE]], [[CONV]]
+; CHECK-NEXT:    ret i32 [[ADD]]
+;
+entry:
+  %wide = load i32, ptr %p, align 4, !noalias !0
+  %p1 = getelementptr inbounds i8, ptr %p, i64 1
+  %narrow = load i8, ptr %p1, align 1
+  %conv = zext i8 %narrow to i32
+  %add = add nsw i32 %wide, %conv
+  ret i32 %add
+}
+
+; Same as above for !alias.scope on the surviving wider load.
+define i32 @alias_scope_dropped_local(ptr %p) {
+; CHECK-LABEL: define i32 @alias_scope_dropped_local(
+; CHECK-SAME: ptr [[P:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[WIDE:%.*]] = load i32, ptr [[P]], align 4
+; CHECK-NEXT:    [[P1:%.*]] = getelementptr inbounds i8, ptr [[P]], i64 1
+; CHECK-NEXT:    [[TMP0:%.*]] = lshr i32 [[WIDE]], 8
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc i32 [[TMP0]] to i8
+; CHECK-NEXT:    [[CONV:%.*]] = zext i8 [[TMP1]] to i32
+; CHECK-NEXT:    [[ADD:%.*]] = add nsw i32 [[WIDE]], [[CONV]]
+; CHECK-NEXT:    ret i32 [[ADD]]
+;
+entry:
+  %wide = load i32, ptr %p, align 4, !alias.scope !0
+  %p1 = getelementptr inbounds i8, ptr %p, i64 1
+  %narrow = load i8, ptr %p1, align 1
+  %conv = zext i8 %narrow to i32
+  %add = add nsw i32 %wide, %conv
+  ret i32 %add
+}
+
+; Cross-block (non-local) coerced load. The i32 load in entry is forwarded to
+; the i8 load at P+1 in the taken block. The surviving i32 load should keep
+; its !noalias.
+define i32 @noalias_dropped_nonlocal(ptr %p) {
+; CHECK-LABEL: define i32 @noalias_dropped_nonlocal(
+; CHECK-SAME: ptr [[P:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    [[WIDE:%.*]] = load i32, ptr [[P]], align 4
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[WIDE]], 127
+; CHECK-NEXT:    [[TMP0:%.*]] = lshr i32 [[WIDE]], 8
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc i32 [[TMP0]] to i8
+; CHECK-NEXT:    br i1 [[CMP]], label %[[T:.*]], label %[[F:.*]]
+; CHECK:       [[T]]:
+; CHECK-NEXT:    [[P1:%.*]] = getelementptr inbounds i8, ptr [[P]], i64 1
+; CHECK-NEXT:    [[CONV:%.*]] = zext i8 [[TMP1]] to i32
+; CHECK-NEXT:    ret i32 [[CONV]]
+; CHECK:       [[F]]:
+; CHECK-NEXT:    ret i32 52
+;
+entry:
+  %wide = load i32, ptr %p, align 4, !noalias !0
+  %cmp = icmp eq i32 %wide, 127
+  br i1 %cmp, label %t, label %f
+
+t:
+  %p1 = getelementptr inbounds i8, ptr %p, i64 1
+  %narrow = load i8, ptr %p1, align 1
+  %conv = zext i8 %narrow to i32
+  ret i32 %conv
+
+f:
+  ret i32 52
+}
+
+; Alias-scope metadata domain.
+!1 = distinct !{!1, !2, !"scope A"}
+!2 = distinct !{!2, !"test domain"}
+
+!0 = !{!1}