[clang] Fix #pragma (packed, n) not emitting the alignment in debug info (PR #94673)

[Augusto Noronha via cfe-commits]

https://github.com/augusto2112 created https://github.com/llvm/llvm-project/pull/94673

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

>From 8fd0e9dcfd915367db1b66001daab47415406302 Mon Sep 17 00:00:00 2001
From: Augusto Noronha <anoronha at apple.com>
Date: Thu, 6 Jun 2024 12:29:05 -0700
Subject: [PATCH] Fix #pragma (packed, n) not emitting the alignment in debug
 info

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
---
 clang/lib/CodeGen/CGDebugInfo.cpp                 | 11 ++++++++++-
 clang/test/CodeGen/debug-info-packed-struct.c     |  4 ++--
 clang/test/CodeGenCXX/debug-info-struct-align.cpp |  8 ++++++++
 3 files changed, 20 insertions(+), 3 deletions(-)

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");