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

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.

Author: stefanp-synopsys

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;
 

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
+
+@keep_this = internal constant [5 x i8] c"keep1", align 1
+@keep_this2 = internal constant [5 x i8] c"keep2", align 1
+@.str.1 = private unnamed_addr constant [12 x i8] c"str1_STRING\00", align 1
+@.str.2 = private unnamed_addr constant [12 x i8] c"str2_STRING\00", align 1
+@.str.3 = private unnamed_addr constant [12 x i8] c"str3_STRING\00", align 1
+@llvm.used = appending global [1 x ptr] [ptr @keep_this], section "llvm.metadata"
+@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"