Fix #pragma (packed, n) not emitting the alignment in debug info

[augusto2112]

Debug info generation won't emit the alignment of types that have a standard alignment. It was not taking into account the that case.

rdar://127785973

[llvmbot]

@llvm/pr-subscribers-debuginfo
@llvm/pr-subscribers-clang-codegen

@llvm/pr-subscribers-clang

Author: Augusto Noronha (augusto2112)

Changes

Debug info generation won't emit the alignment of types that have a standard alignment. It was not taking into account the that case.

rdar://127785973

---

Full diff: https://github.com/llvm/llvm-project/pull/94673.diff

3 Files Affected:

• (modified) clang/lib/CodeGen/CGDebugInfo.cpp (+10-1)
• (modified) clang/test/CodeGen/debug-info-packed-struct.c (+2-2)
• (modified) clang/test/CodeGenCXX/debug-info-struct-align.cpp (+8)

diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index 5f6f911c7a6d6..591e42b1969b4 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -58,7 +58,16 @@ using namespace clang::CodeGen;
 
 static uint32_t getTypeAlignIfRequired(const Type *Ty, const ASTContext &Ctx) {
   auto TI = Ctx.getTypeInfo(Ty);
-  return TI.isAlignRequired() ? TI.Align : 0;
+  if (TI.isAlignRequired())
+    return TI.Align;
+
+  // MaxFieldAlignmentAttr is the attribute added to types 
+  // declared after #pragma pack(n).
+  if (auto *Decl = Ty->getAsRecordDecl())
+    if (Decl->hasAttr<MaxFieldAlignmentAttr>())
+      return TI.Align;
+
+  return 0;
 }
 
 static uint32_t getTypeAlignIfRequired(QualType Ty, const ASTContext &Ctx) {
diff --git a/clang/test/CodeGen/debug-info-packed-struct.c b/clang/test/CodeGen/debug-info-packed-struct.c
index 6441a740e3799..676cdb38b396f 100644
--- a/clang/test/CodeGen/debug-info-packed-struct.c
+++ b/clang/test/CodeGen/debug-info-packed-struct.c
@@ -59,7 +59,7 @@ struct layout2 {
 #pragma pack()
 // CHECK: l2_ofs0
 // CHECK: !DIDerivedType(tag: DW_TAG_member, name: "l2_ofs1",
-// CHECK-SAME:     {{.*}}size: 64, offset: 8)
+// CHECK-SAME:     {{.*}}size: 64, align: 8, offset: 8)
 // CHECK: !DIDerivedType(tag: DW_TAG_member, name: "l2_ofs9",
 // CHECK-SAME:     {{.*}}size: 1, offset: 72, flags: DIFlagBitField, extraData: i64 72)
 
@@ -81,7 +81,7 @@ struct layout3 {
 #pragma pack()
 // CHECK: l3_ofs0
 // CHECK: !DIDerivedType(tag: DW_TAG_member, name: "l3_ofs4",
-// CHECK-SAME:     {{.*}}size: 64, offset: 32)
+// CHECK-SAME:     {{.*}}size: 64, align: 32, offset: 32)
 // CHECK: !DIDerivedType(tag: DW_TAG_member, name: "l3_ofs12",
 // CHECK-SAME:     {{.*}}size: 1, offset: 96, flags: DIFlagBitField, extraData: i64 96)
 
diff --git a/clang/test/CodeGenCXX/debug-info-struct-align.cpp b/clang/test/CodeGenCXX/debug-info-struct-align.cpp
index 1269cbce83ef0..cd91f4c302ddc 100644
--- a/clang/test/CodeGenCXX/debug-info-struct-align.cpp
+++ b/clang/test/CodeGenCXX/debug-info-struct-align.cpp
@@ -25,3 +25,11 @@ struct MyType2 {
 MyType2 mt2;
 
 static_assert(alignof(MyType2) == 1, "alignof MyType2 is wrong");
+
+#pragma pack(1)
+struct MyType3 {
+  int m;
+};
+MyType3 mt3;
+
+static_assert(alignof(MyType3) == 1, "alignof MyType3 is wrong");

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[adrian-prantl]

LGTM