[llvm] a5c8ec4 - [CGDebugInfo] Emit subprograms for decls when AT_tail_call is understood

Wed Nov 6 18:04:45 PST 2019

As a heads up we're starting to see a problem around this commit with
backtraces for inline functions with msan where the line number has
gone away (replaced with 0).

Dave is looking at it, but I thought I'd send a message as early as I could.

-eric

On Mon, Nov 4, 2019 at 3:14 PM Vedant Kumar via llvm-commits
<llvm-commits at lists.llvm.org> wrote:
>
>
> Author: Vedant Kumar
> Date: 2019-11-04T15:14:24-08:00
> New Revision: a5c8ec4baa2c00d8dbca36ffd236a40f9e0c07ed
>
> URL: https://github.com/llvm/llvm-project/commit/a5c8ec4baa2c00d8dbca36ffd236a40f9e0c07ed
> DIFF: https://github.com/llvm/llvm-project/commit/a5c8ec4baa2c00d8dbca36ffd236a40f9e0c07ed.diff
>
> LOG: [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
>
> Added:
>
>
> Modified:
>     clang/lib/CodeGen/CGDebugInfo.cpp
>     clang/test/CodeGen/debug-info-extern-call.c
>     clang/test/CodeGenCXX/dbg-info-all-calls-described.cpp
>     llvm/test/DebugInfo/X86/dwarf-callsite-related-attrs.ll
>
> Removed:
>
>
>
> ################################################################################
> diff  --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
> index e0bb3fda7acf..c0c8fd3c8f16 100644
> --- a/clang/lib/CodeGen/CGDebugInfo.cpp
> +++ b/clang/lib/CodeGen/CGDebugInfo.cpp
> @@ -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;
>
> diff  --git a/clang/test/CodeGen/debug-info-extern-call.c b/clang/test/CodeGen/debug-info-extern-call.c
> index e35669b78f93..7f58fe59a635 100644
> --- a/clang/test/CodeGen/debug-info-extern-call.c
> +++ b/clang/test/CodeGen/debug-info-extern-call.c
> @@ -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);
>
>
> diff  --git a/clang/test/CodeGenCXX/dbg-info-all-calls-described.cpp b/clang/test/CodeGenCXX/dbg-info-all-calls-described.cpp
> index 1cb2b6c609f3..667c2469b55e 100644
> --- a/clang/test/CodeGenCXX/dbg-info-all-calls-described.cpp
> +++ b/clang/test/CodeGenCXX/dbg-info-all-calls-described.cpp
> @@ -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
>
> diff  --git a/llvm/test/DebugInfo/X86/dwarf-callsite-related-attrs.ll b/llvm/test/DebugInfo/X86/dwarf-callsite-related-attrs.ll
> index c37ce1eb7fbe..33e06faba57b 100644
> --- a/llvm/test/DebugInfo/X86/dwarf-callsite-related-attrs.ll
> +++ b/llvm/test/DebugInfo/X86/dwarf-callsite-related-attrs.ll
> @@ -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
>
>
>
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