[llvm] [PowerPC] Do not string pool globals that are part of llvm used. (PR #66848)

[Stefan Pintilie via llvm-commits]

https://github.com/stefanp-ibm updated https://github.com/llvm/llvm-project/pull/66848

>From d03571abb748f34e9fd886a4c83d58322be3078a Mon Sep 17 00:00:00 2001
From: Stefan Pintilie <stefanp at ca.ibm.com>
Date: Tue, 19 Sep 2023 21:09:36 -0500
Subject: [PATCH] [PowerPC] Do not string pool globals that are part of llvm
 used.

The string pooling pass was incorrectly pooling global varables that
were part of llvm.used or llvm.compiler.used. This patch fixes the pass
to prevent that by checking each candidate to make sure that it is not
in either of those lists.
---
 .../lib/Target/PowerPC/PPCMergeStringPool.cpp | 14 +++++
 .../PowerPC/aix-xcoff-used-with-stringpool.ll | 57 +++++++++++++++++++
 2 files changed, 71 insertions(+)
 create mode 100644 llvm/test/CodeGen/PowerPC/aix-xcoff-used-with-stringpool.ll

diff --git a/llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp b/llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp
index a88992c2a8224c2b..d6db056707925428 100644
--- a/llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp
+++ b/llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp
@@ -140,6 +140,16 @@ static bool hasReplaceableUsers(GlobalVariable &GV) {
 // valid candidates to be merged into the string pool. Valid candidates will
 // be added to MergeableStrings.
 void PPCMergeStringPool::collectCandidateConstants(Module &M) {
+  SmallVector<GlobalValue *, 4> UsedV;
+  collectUsedGlobalVariables(M, UsedV, /*CompilerUsed=*/false);
+  SmallVector<GlobalValue *, 4> UsedVCompiler;
+  collectUsedGlobalVariables(M, UsedVCompiler, /*CompilerUsed=*/true);
+  // Combine all of the Global Variables marked as used into a SmallPtrSet for
+  // faster lookup inside the loop.
+  SmallPtrSet<GlobalValue*, 8> AllUsedGlobals;
+  AllUsedGlobals.insert(UsedV.begin(), UsedV.end());
+  AllUsedGlobals.insert(UsedVCompiler.begin(), UsedVCompiler.end());
+
   for (GlobalVariable &Global : M.globals()) {
     LLVM_DEBUG(dbgs() << "Looking at global:");
     LLVM_DEBUG(Global.dump());
@@ -171,6 +181,10 @@ void PPCMergeStringPool::collectCandidateConstants(Module &M) {
     if (!ConstData)
       continue;
 
+    // Do not pool globals that are part of llvm.used or llvm.compiler.end.
+    if (AllUsedGlobals.contains(&Global))
+      continue;
+
     if (!hasReplaceableUsers(Global))
       continue;
 
diff --git a/llvm/test/CodeGen/PowerPC/aix-xcoff-used-with-stringpool.ll b/llvm/test/CodeGen/PowerPC/aix-xcoff-used-with-stringpool.ll
new file mode 100644
index 0000000000000000..fa9a8fb457518aff
--- /dev/null
+++ b/llvm/test/CodeGen/PowerPC/aix-xcoff-used-with-stringpool.ll
@@ -0,0 +1,57 @@
+;; Test that the string pooling pass does not pool globals that are
+;; in llvm.used or in llvm.compiler.used.
+
+; RUN: llc -verify-machineinstrs -mcpu=pwr8 -mtriple powerpc-ibm-aix-xcoff -data-sections=false < %s | \
+; RUN:   FileCheck %s
+
+; RUN: llc -verify-machineinstrs -mcpu=pwr8 -mtriple powerpc64-ibm-aix-xcoff -data-sections=false < %s | \
+; RUN:   FileCheck %s
+
+ at keep_this = internal constant [5 x i8] c"keep1", align 1
+ at keep_this2 = internal constant [5 x i8] c"keep2", align 1
+ at .str.1 = private unnamed_addr constant [12 x i8] c"str1_STRING\00", align 1
+ at .str.2 = private unnamed_addr constant [12 x i8] c"str2_STRING\00", align 1
+ at .str.3 = private unnamed_addr constant [12 x i8] c"str3_STRING\00", align 1
+ at llvm.used = appending global [1 x ptr] [ptr @keep_this], section "llvm.metadata"
+ at llvm.compiler.used = appending global [1 x ptr] [ptr @keep_this2], section "llvm.metadata"
+
+declare signext i32 @callee(ptr noundef)
+
+define dso_local signext i32 @keep1() {
+entry:
+  %call = tail call signext i32 @callee(ptr noundef nonnull @keep_this)
+  ret i32 %call
+}
+
+define dso_local signext i32 @keep2() {
+entry:
+  %call = tail call signext i32 @callee(ptr noundef nonnull @keep_this2)
+  ret i32 %call
+}
+
+define dso_local signext i32 @str1() {
+entry:
+  %call = tail call signext i32 @callee(ptr noundef nonnull @.str.1)
+  ret i32 %call
+}
+
+define dso_local signext i32 @str2() {
+entry:
+  %call = tail call signext i32 @callee(ptr noundef nonnull @.str.2)
+  ret i32 %call
+}
+
+define dso_local signext i32 @str3() {
+entry:
+  %call = tail call signext i32 @callee(ptr noundef nonnull @.str.3)
+  ret i32 %call
+}
+
+; CHECK:    .lglobl keep_this
+; CHECK:  keep_this:
+; CHECK:    .lglobl keep_this2
+; CHECK:  keep_this2:
+; CHECK:  L..__ModuleStringPool:
+; CHECK:    .string "str1_STRING"
+; CHECK:    .string "str2_STRING"
+; CHECK:    .string "str3_STRING"