Commit a5c8ec4b authored by Vedant Kumar's avatar Vedant Kumar
Browse files

[CGDebugInfo] Emit subprograms for decls when AT_tail_call is understood 

Currently, clang emits subprograms for declared functions when the
target debugger or DWARF standard is known to support entry values
(DW_OP_entry_value & the GNU equivalent).

Treat DW_AT_tail_call the same way to allow debuggers to follow cross-TU
tail calls.

Pre-patch debug session with a cross-TU tail call:

```
  * frame #0: 0x0000000100000fa4 main`target at b.c:4:3 [opt]
    frame #1: 0x0000000100000f99 main`main at a.c:8:10 [opt]
```

Post-patch (note that the tail-calling frame, "helper", is visible):

```
  * frame #0: 0x0000000100000fa4 main`target at b.c:4:3 [opt]
    frame #1: 0x0000000100000f80 main`helper [opt] [artificial]
    frame #2: 0x0000000100000f99 main`main at a.c:8:10 [opt]
```

rdar://46577651

Differential Revision: https://reviews.llvm.org/D69743
parent dc34b1c9

clang/lib/CodeGen/CGDebugInfo.cpp

+4 −6
Original line number Diff line number Diff line
@@ -3748,9 +3748,7 @@ void CGDebugInfo::EmitFunctionDecl(GlobalDecl GD, SourceLocation Loc, 
void CGDebugInfo::EmitFuncDeclForCallSite(llvm::CallBase *CallOrInvoke,

                                          QualType CalleeType,

                                          const FunctionDecl *CalleeDecl) {

  auto &CGOpts = CGM.getCodeGenOpts();

  if (!CGOpts.EnableDebugEntryValues || !CGM.getLangOpts().Optimize ||

      !CallOrInvoke)

  if (!CallOrInvoke || getCallSiteRelatedAttrs() == llvm::DINode::FlagZero)

    return;



  auto *Func = CallOrInvoke->getCalledFunction();
@@ -4824,10 +4822,10 @@ llvm::DINode::DIFlags CGDebugInfo::getCallSiteRelatedAttrs() const { 
  bool SupportsDWARFv4Ext =

      CGM.getCodeGenOpts().DwarfVersion == 4 &&

      (CGM.getCodeGenOpts().getDebuggerTuning() == llvm::DebuggerKind::LLDB ||

       (CGM.getCodeGenOpts().EnableDebugEntryValues &&

       CGM.getCodeGenOpts().getDebuggerTuning() == llvm::DebuggerKind::GDB));

       CGM.getCodeGenOpts().getDebuggerTuning() == llvm::DebuggerKind::GDB);



  if (!SupportsDWARFv4Ext && CGM.getCodeGenOpts().DwarfVersion < 5)

  if (!SupportsDWARFv4Ext && CGM.getCodeGenOpts().DwarfVersion < 5 &&

      !CGM.getCodeGenOpts().EnableDebugEntryValues)

    return llvm::DINode::FlagZero;



  return llvm::DINode::FlagAllCallsDescribed;

clang/test/CodeGen/debug-info-extern-call.c

+17 −4
Original line number Diff line number Diff line 
// RUN: %clang -Xclang -femit-debug-entry-values -g -O2 -target x86_64-none-linux-gnu -S -emit-llvm %s -o - | FileCheck %s -check-prefix=CHECK-EXT

// CHECK-EXT: !DISubprogram(name: "fn1"

// When entry values are emitted, expect a subprogram for extern decls so that

// the dwarf generator can describe call site parameters at extern call sites.

//

// RUN: %clang -Xclang -femit-debug-entry-values -g -O2 -target x86_64-none-linux-gnu -S -emit-llvm %s -o - | FileCheck %s -check-prefix=ENTRY-VAL

// ENTRY-VAL: !DISubprogram(name: "fn1"



// RUN: %clang -g -O2 -target x86_64-none-linux-gnu -S -emit-llvm %s -o - | FileCheck %s

// CHECK-NOT: !DISubprogram(name: "fn1"

// Similarly, when the debugger tuning is gdb, expect a subprogram for extern

// decls so that the dwarf generator can describe information needed for tail

// call frame reconstrution.

//

// RUN: %clang -g -O2 -target x86_64-none-linux-gnu -ggdb -S -emit-llvm %s -o - | FileCheck %s -check-prefix=GDB

// GDB: !DISubprogram(name: "fn1"

//

// Do not emit a subprogram for extern decls when entry values are disabled and

// the tuning is not set to gdb.

//

// RUN: %clang -g -O2 -target x86_64-none-linux-gnu -gsce -S -emit-llvm %s -o - | FileCheck %s -check-prefix=SCE

// SCE-NOT: !DISubprogram(name: "fn1"



extern int fn1(int a, int b);

clang/test/CodeGenCXX/dbg-info-all-calls-described.cpp

+1 −0
Original line number Diff line number Diff line
@@ -56,6 +56,7 @@ 


// NO-ATTR-NOT: FlagAllCallsDescribed



// HAS-ATTR-DAG: DISubprogram(name: "declaration1", {{.*}}, flags: DIFlagPrototyped

// HAS-ATTR-DAG: DISubprogram(name: "declaration2", {{.*}}, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition

// HAS-ATTR-DAG: DISubprogram(name: "struct1", {{.*}}, flags: DIFlagPrototyped, spFlags: DISPFlagOptimized)

// HAS-ATTR-DAG: DISubprogram(name: "struct1", {{.*}}, flags: DIFlagPrototyped | DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition

llvm/test/DebugInfo/X86/dwarf-callsite-related-attrs.ll

+9 −0
Original line number Diff line number Diff line
@@ -25,6 +25,14 @@ 


@sink = global i32 0, align 4, !dbg !0



define void @__has_no_subprogram() {

entry:

  %0 = load volatile i32, i32* @sink, align 4

  %inc = add nsw i32 %0, 1

  store volatile i32 %inc, i32* @sink, align 4

  ret void

}



; ASM: DW_TAG_subprogram

; ASM:   DW_AT_call_all_calls

; OBJ: [[bat_sp:.*]]: DW_TAG_subprogram
@@ -70,6 +78,7 @@ entry: 
; OBJ:     DW_AT_call_tail_call

define void @_Z3foov() !dbg !25 {

entry:

  tail call void @__has_no_subprogram()

  tail call void @_Z3barv(), !dbg !26

  tail call void @_Z3batv(), !dbg !27

  tail call void @_Z3barv(), !dbg !26