[llvm] llvm-reduce: Avoid using constantdata uselistorder in thinlto test (PR #136288)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm created https://github.com/llvm/llvm-project/pull/136288

This also demonstrates a bug that's a consequence of the two different
paths for the single and multithreaded cases. The parallel path goes
through bitcode serialization and does preserve the uselistorder. It
therefore survives and we can observe a reduced uselistorder with deleted
instructions. In the CloneModule case, nothing is reduced.

>From 8c8a4bc09455e500c76b525888ac2fdc1909c996 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Fri, 18 Apr 2025 11:55:24 +0200
Subject: [PATCH] llvm-reduce: Avoid using constantdata uselistorder in thinlto
 test

This also demonstrates a bug that's a consequence of the two different
paths for the single and multithreaded cases. The parallel path goes
through bitcode serialization and does preserve the uselistorder. It
therefore survives and we can observe a reduced uselistorder with deleted
instructions. In the CloneModule case, nothing is reduced.
---
 .../thinlto-preserve-uselistorder.ll          | 59 ++++++++++++++-----
 1 file changed, 44 insertions(+), 15 deletions(-)

diff --git a/llvm/test/tools/llvm-reduce/thinlto-preserve-uselistorder.ll b/llvm/test/tools/llvm-reduce/thinlto-preserve-uselistorder.ll
index 2332f2d632911..eac3e462aab8a 100644
--- a/llvm/test/tools/llvm-reduce/thinlto-preserve-uselistorder.ll
+++ b/llvm/test/tools/llvm-reduce/thinlto-preserve-uselistorder.ll
@@ -1,19 +1,48 @@
-; RUN: opt --thinlto-bc --thinlto-split-lto-unit %s -o %t.0
-; RUN: llvm-reduce -write-tmp-files-as-bitcode --delta-passes=instructions %t.0 -o %t.1 \
+; RUN: opt --preserve-bc-uselistorder --thinlto-bc --thinlto-split-lto-unit %s -o %t.0
+
+; RUN: llvm-reduce -j=2 --delta-passes=instructions %t.0 -o %t.1 \
 ; RUN:     --test %python --test-arg %p/Inputs/llvm-dis-and-filecheck.py --test-arg llvm-dis --test-arg FileCheck --test-arg --check-prefix=INTERESTING --test-arg %s
 ; RUN: llvm-dis --preserve-ll-uselistorder %t.1 -o %t.2
-; RUN: FileCheck --check-prefix=RESULT %s < %t.2
-
-define i32 @func(i32 %arg0, i32 %arg1) {
-entry:
-  %add0 = add i32 %arg0, 0
-  %add1 = add i32 %add0, 0
-  %add2 = add i32 %add1, 0
-  %add3 = add i32 %arg1, 0
-  %add4 = add i32 %add2, %add3
-  ret i32 %add4
+; RUN: FileCheck --check-prefixes=RESULT,RESULT-PARALLEL %s < %t.2
+
+; FIXME: The single thread path uses CloneModule, which does not
+; preserve uselistorder. Consequently it is incapable of reducing
+; anything a case that depends on uselistorder.
+
+; RUN: llvm-reduce -j=1 --delta-passes=instructions %t.0 -o %t.3 \
+; RUN:     --test %python --test-arg %p/Inputs/llvm-dis-and-filecheck.py --test-arg llvm-dis --test-arg FileCheck --test-arg --check-prefix=INTERESTING --test-arg %s
+; RUN: llvm-dis --preserve-ll-uselistorder %t.3 -o %t.4
+; RUN: FileCheck --check-prefixes=RESULT,RESULT-SINGLE %s < %t.4
+
+ at gv0 = external global [0 x i8]
+
+; RESULT-LABEL: @func(
+; RESULT-PARALLEL-NEXT: %gep0 = getelementptr i8, ptr @gv0, i32 %arg0
+; RESULT-PARALLEL-NEXT: %gep1 = getelementptr i8, ptr @gv0, i32 %arg1
+; RESULT-PARALLEL-NEXT: ret void
+
+; RESULT-SINGLE: ptr @gv0
+; RESULT-SINGLE: ptr @gv0
+; RESULT-SINGLE: ptr @gv0
+; RESULT-SINGLE: ptr @gv0
+; RESULT-SINGLE: ptr @gv0
+define void @func(i32 %arg0, i32 %arg1, i32 %arg2, i32 %arg3) {
+  %gep0 = getelementptr i8, ptr @gv0, i32 %arg0
+  %gep1 = getelementptr i8, ptr @gv0, i32 %arg1
+  %gep2 = getelementptr i8, ptr @gv0, i32 %arg2
+  %gep3 = getelementptr i8, ptr @gv0, i32 %arg3
+  store i32 0, ptr %gep0
+  store i32 0, ptr %gep1
+  store i32 0, ptr %gep2
+  store i32 0, ptr %gep3
+  store i32 0, ptr @gv0
+  ret void
 }
 
-; INTERESTING: uselistorder i32 0
-; RESULT: uselistorder i32 0, { 0, 2, 1 }
-uselistorder i32 0, { 3, 2, 1, 0 }
+; INTERESTING: uselistorder ptr
+
+; RESULT: uselistorder directives
+; RESULT-PARALLEL: uselistorder ptr @gv0, { 1, 0 }
+; RESULT-SINGLE: uselistorder ptr @gv0, { 3, 4, 2, 1, 0 }
+
+uselistorder ptr @gv0, { 3, 4, 2, 1, 0 }