[llvm] r348806 - debuginfo: Use symbol difference for CU length to simplify assembly reading/editing
David Blaikie via llvm-commits
llvm-commits at lists.llvm.org
Tue Dec 11 15:34:44 PST 2018
Reverted in 348898 due to a Google-internal failure still being
investigated (looks like some other path to build code for ptxas without
being "isNVPTX" I guess?).
On Mon, Dec 10, 2018 at 2:47 PM David Blaikie via llvm-commits <
llvm-commits at lists.llvm.org> wrote:
> Author: dblaikie
> Date: Mon Dec 10 14:44:48 2018
> New Revision: 348806
>
> URL: http://llvm.org/viewvc/llvm-project?rev=348806&view=rev
> Log:
> debuginfo: Use symbol difference for CU length to simplify assembly
> reading/editing
>
> Mucking about simplifying a test case ( https://reviews.llvm.org/D55261 )
> I stumbled across something I've hit before - that LLVM's (GCC's does too,
> FWIW) assembly output includes a hardcode length for a DWARF unit in its
> header. Instead we could emit a label difference - making the assembly
> easier to read/edit (though potentially at a slight (I haven't tried to
> observe it) performance cost of delaying/sinking the length computation
> into the MC layer).
>
> Reviewers: JDevlieghere, probinson, ABataev
>
> Differential Revision: https://reviews.llvm.org/D55281
>
> Modified:
> llvm/trunk/lib/CodeGen/AsmPrinter/DwarfFile.cpp
> llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
> llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.h
> llvm/trunk/test/DebugInfo/X86/sections_as_references.ll
>
> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfFile.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfFile.cpp?rev=348806&r1=348805&r2=348806&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfFile.cpp (original)
> +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfFile.cpp Mon Dec 10 14:44:48
> 2018
> @@ -46,6 +46,8 @@ void DwarfFile::emitUnit(DwarfUnit *TheU
> TheU->emitHeader(UseOffsets);
>
> Asm->emitDwarfDIE(Die);
> +
> + Asm->OutStreamer->EmitLabel(TheU->getEndLabel());
> }
>
> // Compute the size and offset for each DIE.
>
> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp?rev=348806&r1=348805&r2=348806&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp (original)
> +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.cpp Mon Dec 10 14:44:48
> 2018
> @@ -38,6 +38,7 @@
> #include "llvm/Support/Casting.h"
> #include "llvm/Support/CommandLine.h"
> #include "llvm/Target/TargetLoweringObjectFile.h"
> +#include "llvm/Target/TargetMachine.h"
> #include <cassert>
> #include <cstdint>
> #include <string>
> @@ -1553,7 +1554,17 @@ DIE *DwarfUnit::getOrCreateStaticMemberD
> void DwarfUnit::emitCommonHeader(bool UseOffsets, dwarf::UnitType UT) {
> // Emit size of content not including length itself
> Asm->OutStreamer->AddComment("Length of Unit");
> - Asm->emitInt32(getHeaderSize() + getUnitDie().getSize());
> + StringRef Prefix = isDwoUnit() ? "debug_info_dwo_" : "debug_info_";
> + MCSymbol *BeginLabel = Asm->createTempSymbol(Prefix + "start");
> + EndLabel = Asm->createTempSymbol(Prefix + "end");
> +
> + // Use a label difference for the convenience of legible/easily modified
> + // assembly - except on NVPTX where label differences aren't supported.
> + if (Asm->TM.getTargetTriple().isNVPTX())
> + Asm->emitInt32(getHeaderSize() + getUnitDie().getSize());
> + else
> + Asm->EmitLabelDifference(EndLabel, BeginLabel, 4);
> + Asm->OutStreamer->EmitLabel(BeginLabel);
>
> Asm->OutStreamer->AddComment("DWARF version number");
> unsigned Version = DD->getDwarfVersion();
>
> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.h?rev=348806&r1=348805&r2=348806&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.h (original)
> +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfUnit.h Mon Dec 10 14:44:48 2018
> @@ -48,6 +48,7 @@ protected:
>
> /// Target of Dwarf emission.
> AsmPrinter *Asm;
> + MCSymbol *EndLabel;
>
> // Holders for some common dwarf information.
> DwarfDebug *DD;
> @@ -82,6 +83,7 @@ protected:
> public:
> // Accessors.
> AsmPrinter* getAsmPrinter() const { return Asm; }
> + MCSymbol *getEndLabel() const { return EndLabel; }
> uint16_t getLanguage() const { return CUNode->getSourceLanguage(); }
> const DICompileUnit *getCUNode() const { return CUNode; }
>
>
> Modified: llvm/trunk/test/DebugInfo/X86/sections_as_references.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/DebugInfo/X86/sections_as_references.ll?rev=348806&r1=348805&r2=348806&view=diff
>
> ==============================================================================
> --- llvm/trunk/test/DebugInfo/X86/sections_as_references.ll (original)
> +++ llvm/trunk/test/DebugInfo/X86/sections_as_references.ll Mon Dec 10
> 14:44:48 2018
> @@ -9,13 +9,19 @@
> ; CHECK-NOT: .L
>
> ; CHECK: .section .debug_info
> -; CHECK-NOT: .L
> -; CHECK: .short 2 # DWARF version number
> +; CHECK-NEXT: .long .Ldebug_info_end0-.Ldebug_info_start0 # Length of Unit
> +; CHECK-NEXT: .Ldebug_info_start0:
> +; CHECK-NEXT: .short 2 # DWARF version number
> ; CHECK-NOT: .L
> ; CHECK: .long .debug_abbrev # Offset Into Abbrev. Section
> ; CHECK-NOT: .L
> ; CHECK: .long .debug_line # DW_AT_stmt_list
> ; CHECK-NOT: .L
> +; CHECK: .Ldebug_info_end0:
> +; CHECK-NOT: .L
> +; CHECK: .long .Ldebug_info_end1-.Ldebug_info_start1 # Length of Unit
> +; CHECK-NEXT: .Ldebug_info_start1:
> +; CHECK-NOT: .L
> ; CHECK: .long .debug_abbrev # Offset Into Abbrev. Section
> ; CHECK-NOT: .L
> ; CHECK: .long .debug_line # DW_AT_stmt_list
> @@ -23,6 +29,7 @@
> ; CHECK: .quad .debug_info+{{[0-9]+}} # DW_AT_type
> ; CHECK-NOT: .L
> ; CHECK: .byte 0 # End Of Children Mark
> +; CHECK-NEXT: .Ldebug_info_end1:
> ; CHECK-NOT: .L
>
> source_filename = "test/DebugInfo/X86/sections_as_references.ll"
>
>
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