[llvm] Add support to meger strings used by metadata (PR #77364)

[Shimin Cui via llvm-commits]

https://github.com/scui-ibm created https://github.com/llvm/llvm-project/pull/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.

>From 67cf77a4dbb07407812d30efd5c3cc38def9fa3c Mon Sep 17 00:00:00 2001
From: Shimin Cui <scui at ca.ibm.com>
Date: Mon, 8 Jan 2024 14:45:26 -0500
Subject: [PATCH] Add support to meger strings used by metadata

---
 .../lib/Target/PowerPC/PPCMergeStringPool.cpp | 11 ++++
 .../PowerPC/merge-string-used-by-metadata.mir | 54 +++++++++++++++++++
 2 files changed, 65 insertions(+)
 create mode 100644 llvm/test/CodeGen/PowerPC/merge-string-used-by-metadata.mir

diff --git a/llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp b/llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp
index d9465e86d89662..ab9cfed3079734 100644
--- a/llvm/lib/Target/PowerPC/PPCMergeStringPool.cpp
+++ b/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();
diff --git a/llvm/test/CodeGen/PowerPC/merge-string-used-by-metadata.mir b/llvm/test/CodeGen/PowerPC/merge-string-used-by-metadata.mir
new file mode 100644
index 00000000000000..2a791966be4ecf
--- /dev/null
+++ b/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)
+
+...