Add support to meger strings used by metadata (#77364)

Currently if the merged string is used by metadata, its metadata uses
are not replaced if the string is merged. This is to add code support
for the metadata use replacement.

Author: scui-ibm

llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp

@@ -268,6 +268,17 @@ bool PPCMergeStringPool::mergeModuleStringPool(Module &M) {
     // before every use in order to compute this offset.
     replaceUsesWithGEP(GV, PooledGlobal, ElementIndex);
 
+    // Replace all the uses by metadata.
+    if (GV->isUsedByMetadata()) {
+      Constant *Indices[2] = {
+          ConstantInt::get(Type::getInt32Ty(*Context), 0),
+          ConstantInt::get(Type::getInt32Ty(*Context), ElementIndex)};
+      Constant *ConstGEP = ConstantExpr::getInBoundsGetElementPtr(
+          PooledStructType, PooledGlobal, Indices);
+      ValueAsMetadata::handleRAUW(GV, ConstGEP);
+    }
+    assert(!GV->isUsedByMetadata() && "Should be no metadata use anymore");
+
     // This GV has no more uses so we can erase it.
     if (GV->use_empty())
       GV->eraseFromParent();

llvm/test/CodeGen/PowerPC/merge-string-used-by-metadata.mir

@@ -0,0 +1,54 @@
+# RUN: llc -run-pass=ppc-merge-strings -mcpu=pwr8 -mtriple powerpc64le-unknown-linux-gnu \
+# RUN:   -verify-machineinstrs -o - %s | FileCheck %s
+# RUN: llc -run-pass=ppc-merge-strings -mcpu=pwr8 -mtriple powerpc64-ibm-aix-xcoff \
+# RUN:   -verify-machineinstrs -o - %s | FileCheck %s
+
+--- |
+  ; Constants list.
+  @const.1 = internal constant [7 x i8] c"const1\00", align 1
+  @const.2 = internal constant [7 x i8] c"const2\00", align 1
+
+  ;;
+  ;; Start of test code.
+  ;;
+
+  define noundef ptr @func1(ptr noundef nonnull align 8 dereferenceable(8) %this) #0 !dbg !6 {
+  ; CHECK-LABEL: func1
+  ; CHECK:       %0 = getelementptr { [7 x i8], [7 x i8] }, ptr @__ModuleStringPool, i32 0, i32 1
+  ; CHECK-NEXT:  ret ptr %0, !dbg !14
+  entry:
+    ret ptr @const.2, !dbg !14
+  }
+
+  define noundef ptr @func2(ptr noundef nonnull align 8 dereferenceable(8) %this) #0 {
+  ; CHECK-LABEL: func2
+  ; CHECK:       %0 = getelementptr { [7 x i8], [7 x i8] }, ptr @__ModuleStringPool, i32 0, i32 0
+  ; CHECK-NEXT:  ret ptr %0
+  entry:
+    ret ptr @const.1
+  }
+
+  attributes #0 = { noinline nounwind "frame-pointer"="all" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="pwr8" "target-features"="+altivec,+bpermd,+crbits,+crypto,+direct-move,+extdiv,+htm,+isa-v206-instructions,+isa-v207-instructions,+power8-vector,+quadword-atomics,+vsx,-aix-small-local-exec-tls,-isa-v30-instructions,-power9-vector,-privileged,-rop-protect,-spe" }
+
+  !llvm.dbg.cu = !{!0}
+  !llvm.module.flags = !{!3, !4}
+  !llvm.ident = !{!5}
+
+  ; CHECK:       !10 = !DITemplateValueParameter(name: "ID", type: !11, value: ptr getelementptr inbounds ({ [7 x i8], [7 x i8] }, ptr @__ModuleStringPool, i32 0, i32 1))
+  !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !1, isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, retainedTypes: !2, globals: !2, imports: !2)
+  !1 = !DIFile(filename: "constant-pointers.cpp", directory: "/tmp/dbginfo")
+  !2 = !{}
+  !3 = !{i32 7, !"Dwarf Version", i32 3}
+  !4 = !{i32 2, !"Debug Info Version", i32 3}
+  !5 = !{!"clang version 17.0.0"}
+  !6 = distinct !DISubprogram(name: "getId", linkageName: "func1", scope: !1, file: !1, line: 2, type: !7, scopeLine: 2, virtualIndex: 6, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, templateParams: !9, retainedNodes: !2)
+  !7 = !DISubroutineType(types: !8)
+  !8 = !{null}
+  !9 = !{!10}
+  !10 = !DITemplateValueParameter(name: "ID", type: !11, value: ptr @const.2)
+  !11 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !12, size: 64)
+  !12 = !DIDerivedType(tag: DW_TAG_const_type, baseType: !13)
+  !13 = !DIBasicType(name: "char", size: 8, encoding: DW_ATE_unsigned_char)
+  !14 = !DILocation(line: 3, scope: !6)
+
+...