Debug Info: Support DW_AT_calling_convention on composite types.

This implements the DWARF 5 feature described at
http://www.dwarfstd.org/ShowIssue.php?issue=141215.1

This allows a consumer to understand whether a composite data type is
trivially copyable and thus should be passed by value instead of by
reference. The canonical example is being able to distinguish the
following two types:

  // S is not trivially copyable because of the explicit destructor.
  struct S {
     ~S() {}
  };

  // T is a POD type.
  struct T {
     ~T() = default;
  };

This patch adds two new (DI)flags to LLVM metadata: TypePassByValue
and TypePassByReference.

<rdar://problem/36034922>
Differential Revision: https://reviews.llvm.org/D41743

llvm-svn: 321844

llvm/include/llvm-c/DebugInfo.h

@@ -52,6 +52,8 @@ typedef enum {
   LLVMDIFlagBitField = 1 << 19,
   LLVMDIFlagNoReturn = 1 << 20,
   LLVMDIFlagMainSubprogram = 1 << 21,
+  LLVMDIFlagTypePassByValue = 1 << 22,
+  LLVMDIFlagTypePassByReference = 1 << 23,
   LLVMDIFlagIndirectVirtualBase = (1 << 2) | (1 << 5),
   LLVMDIFlagAccessibility = LLVMDIFlagPrivate | LLVMDIFlagProtected |
                             LLVMDIFlagPublic,

llvm/include/llvm/IR/DebugInfoFlags.def

@@ -43,6 +43,8 @@ HANDLE_DI_FLAG((1 << 18), IntroducedVirtual)
 HANDLE_DI_FLAG((1 << 19), BitField)
 HANDLE_DI_FLAG((1 << 20), NoReturn)
 HANDLE_DI_FLAG((1 << 21), MainSubprogram)
+HANDLE_DI_FLAG((1 << 22), TypePassByValue)
+HANDLE_DI_FLAG((1 << 23), TypePassByReference)
 
 // To avoid needing a dedicated value for IndirectVirtualBase, we use
 // the bitwise or of Virtual and FwdDecl, which does not otherwise
@@ -52,7 +54,7 @@ HANDLE_DI_FLAG((1 << 2) | (1 << 5), IndirectVirtualBase)
 #ifdef DI_FLAG_LARGEST_NEEDED
 // intended to be used with ADT/BitmaskEnum.h
 // NOTE: always must be equal to largest flag, check this when adding new flag
-HANDLE_DI_FLAG((1 << 21), Largest)
+HANDLE_DI_FLAG((1 << 23), Largest)
 #undef DI_FLAG_LARGEST_NEEDED
 #endif
 

llvm/include/llvm/IR/DebugInfoMetadata.h

@@ -633,6 +633,10 @@ class DIType : public DIScope {
   bool isStaticMember() const { return getFlags() & FlagStaticMember; }
   bool isLValueReference() const { return getFlags() & FlagLValueReference; }
   bool isRValueReference() const { return getFlags() & FlagRValueReference; }
+  bool isTypePassByValue() const { return getFlags() & FlagTypePassByValue; }
+  bool isTypePassByReference() const {
+    return getFlags() & FlagTypePassByReference;
+  }
 
   static bool classof(const Metadata *MD) {
     switch (MD->getMetadataID()) {

llvm/lib/CodeGen/AsmPrinter/DwarfUnit.cpp

@@ -975,6 +975,15 @@ void DwarfUnit::constructTypeDIE(DIE &Buffer, const DICompositeType *CTy) {
         Tag == dwarf::DW_TAG_structure_type || Tag == dwarf::DW_TAG_union_type)
       addTemplateParams(Buffer, CTy->getTemplateParams());
 
+    // Add the type's non-standard calling convention.
+    uint8_t CC = 0;
+    if (CTy->isTypePassByValue())
+      CC = dwarf::DW_CC_pass_by_value;
+    else if (CTy->isTypePassByReference())
+      CC = dwarf::DW_CC_pass_by_reference;
+    if (CC)
+      addUInt(Buffer, dwarf::DW_AT_calling_convention, dwarf::DW_FORM_data1,
+              CC);
     break;
   }
   default:

llvm/lib/IR/Verifier.cpp

@@ -905,9 +905,12 @@ void Verifier::visitDIDerivedType(const DIDerivedType &N) {
   }
 }
 
+/// Detect mutually exclusive flags.
 static bool hasConflictingReferenceFlags(unsigned Flags) {
-  return (Flags & DINode::FlagLValueReference) &&
-         (Flags & DINode::FlagRValueReference);
+  return ((Flags & DINode::FlagLValueReference) &&
+          (Flags & DINode::FlagRValueReference)) ||
+         ((Flags & DINode::FlagTypePassByValue) &&
+          (Flags & DINode::FlagTypePassByReference));
 }
 
 void Verifier::visitTemplateParams(const MDNode &N, const Metadata &RawParams) {

llvm/test/DebugInfo/Generic/pass-by-value.ll

@@ -0,0 +1,63 @@
+; RUN: %llc_dwarf -O0 -filetype=obj < %s | llvm-dwarfdump -debug-info - | FileCheck %s
+;
+; // S is not trivially copyable.
+; struct S {
+;    ~S() {}
+; };
+;
+; // T is a POD.
+; struct T {
+;    ~T() = default;
+; };
+;  
+; S s;
+; T t;
+;
+; CHECK: DW_TAG_structure_type
+; CHECK-NEXT: DW_AT_calling_convention	(DW_CC_pass_by_reference)
+; CHECK-NEXT: DW_AT_name	("S")
+;
+; CHECK: DW_TAG_structure_type
+; CHECK-NEXT: DW_AT_calling_convention	(DW_CC_pass_by_value)
+; CHECK-NEXT: DW_AT_name	("T")
+
+source_filename = "pass.cpp"
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.13.0"
+
+%struct.S = type { i8 }
+%struct.T = type { i8 }
+
+@s = global %struct.S zeroinitializer, align 1, !dbg !0
+@__dso_handle = external hidden global i8
+@t = global %struct.T zeroinitializer, align 1, !dbg !6
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!20, !21, !22, !23}
+!llvm.ident = !{!24}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "s", scope: !2, file: !3, line: 9, type: !14, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "clang version 7.0.0 (trunk 321763) (llvm/trunk 321758)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5)
+!3 = !DIFile(filename: "pass.cpp", directory: "/")
+!4 = !{}
+!5 = !{!0, !6}
+!6 = !DIGlobalVariableExpression(var: !7, expr: !DIExpression())
+!7 = distinct !DIGlobalVariable(name: "t", scope: !2, file: !3, line: 10, type: !8, isLocal: false, isDefinition: true)
+!8 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "T", file: !3, line: 5, size: 8, elements: !9, identifier: "_ZTS1T", flags: DIFlagTypePassByValue)
+!9 = !{!10}
+!10 = !DISubprogram(name: "~T", scope: !8, file: !3, line: 6, type: !11, isLocal: false, isDefinition: false, scopeLine: 6, flags: DIFlagPrototyped, isOptimized: false)
+!11 = !DISubroutineType(types: !12)
+!12 = !{null, !13}
+!13 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !8, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!14 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "S", file: !3, line: 1, size: 8, elements: !15, identifier: "_ZTS1S", flags: DIFlagTypePassByReference)
+!15 = !{!16}
+!16 = !DISubprogram(name: "~S", scope: !14, file: !3, line: 2, type: !17, isLocal: false, isDefinition: false, scopeLine: 2, flags: DIFlagPrototyped, isOptimized: false)
+!17 = !DISubroutineType(types: !18)
+!18 = !{null, !19}
+!19 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !14, size: 64, flags: DIFlagArtificial | DIFlagObjectPointer)
+!20 = !{i32 2, !"Dwarf Version", i32 4}
+!21 = !{i32 2, !"Debug Info Version", i32 3}
+!22 = !{i32 1, !"wchar_size", i32 4}
+!23 = !{i32 7, !"PIC Level", i32 2}
+!24 = !{!"clang version 7.0.0 (trunk 321763) (llvm/trunk 321758)"}

llvm/test/Verifier/cc-flags.ll

@@ -0,0 +1,5 @@
+; RUN: not opt -S < %s 2>&1 | FileCheck %s
+
+!named = !{!0}
+!0 = !DICompositeType(tag: DW_TAG_structure_type, name: "A", size: 1, flags: DIFlagTypePassByReference | DIFlagTypePassByValue)
+; CHECK: invalid reference flags