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[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
This commit is contained in:
Vedant Kumar 2019-11-01 17:20:38 -07:00
parent dc34b1c94d
commit a5c8ec4baa
4 changed files with 31 additions and 10 deletions
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10
clang/lib/CodeGen/CGDebugInfo.cpp
View File

@ -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;

21
clang/test/CodeGen/debug-info-extern-call.c
View File

@ -1,8 +1,21 @@
// 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);

1
clang/test/CodeGenCXX/dbg-info-all-calls-described.cpp
View File

@ -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

9
llvm/test/DebugInfo/X86/dwarf-callsite-related-attrs.ll
View File

@ -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