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

Author: augusto2112

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) {

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)
 

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");