[llvm] r239380 - [DWARF] Fix a few corner cases in expression emission
Frédéric Riss
friss at apple.com
Thu Jun 11 10:11:13 PDT 2015
> On Jun 10, 2015, at 8:16 PM, Keno Fischer <kfischer at college.harvard.edu> wrote:
>
> Well, I found what the problem is, but I'm not really sure how to fix it properly.
>
> Basically, the code for that function ends up looking like
>
> DBG_VALUE %RDI, %noreg, !"d", <<0x3cd2840>>; line no:59
> DBG_VALUE %EDI, %noreg, !"d", <<0x3cd2840>>; line no:59
> MOV32mr %RIP, 1, %noreg, <ga:@values>, %noreg, %EDI, %RDI<imp-use,kill>; mem:ST4[getelementptr inbounds ([50 x %struct.some_struct], [50 x %struct.some_struct]* @values, i64 0, i64 0, i32 0)](align=16)(tbaa=<0x3cdd0b8>) dbg:break1.c:59:43
> RETQ; dbg:break1.c:59:48
>
> so when we emit DWARF information we used to first emit an empty range for RDI and then have EDI cover the rest of the function. I see why the second DBG_VALUE was inserted by LLVM (the 32bit subregister could be a different one, so having that information could increase debug info coverage). I think the best way to fix this would be to implement the ability to represent values that are simultaneously in multiple places ( I want this for other reasons too, but it seems to me that that would fix this situation quite elegantly ).
IIRC, the “a value is present in only one place” is pretty fundamental to the way DbgValueHistoryCalculator works today. I totally agree this is broken, there is no reason why a new DBG_VALUE should end the lifetime of the preceding one for the same value (the pass tries to look at the underlying registers lifetime anyway).
Fred
> Basically what I had in mind is separating the notion of a value being present somewhere and having been given a new value. Right now DBG_VALUE is doing both, which is causing the current situation. If instead the code generator knew that `d` is present in both RDI and EDI, it could figure out the most optimal debug information for this function, which is that `d` is in RDI for the entire function. Anyway, I would like to discuss this and will bring it up in the llvmdev thread that Adrian was intending to start. For now, I'll put this change on ice until a proper solution is found.
>
> On Tue, Jun 9, 2015 at 2:06 PM, David Blaikie <dblaikie at gmail.com <mailto:dblaikie at gmail.com>> wrote:
>
>
> On Mon, Jun 8, 2015 at 9:05 PM, David Blaikie <dblaikie at gmail.com <mailto:dblaikie at gmail.com>> wrote:
> Looks like this might've caused:
>
> http://lab.llvm.org:8011/builders/clang-x86_64-ubuntu-gdb-75/builds/22562 <https://urldefense.proofpoint.com/v2/url?u=http-3A__lab.llvm.org-3A8011_builders_clang-2Dx86-5F64-2Dubuntu-2Dgdb-2D75_builds_22562&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=0oGGOb6Hp5KjOM-NE05Xa2gS8lkl1d6kAE-t2drPTA0&s=Ale7iUh7_NXeUQkT2KQ43W-UfMYAyOS3alQ4GJ9ajpo&e=>
>
> Reverted in r239420 to hopefully get the buildbot back to green.
>
>
>
> On Mon, Jun 8, 2015 at 6:54 PM, Keno Fischer <kfischer at college.harvard.edu <mailto:kfischer at college.harvard.edu>> wrote:
> Author: kfischer
> Date: Mon Jun 8 20:53:59 2015
> New Revision: 239380
>
> URL: http://llvm.org/viewvc/llvm-project?rev=239380&view=rev <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject-3Frev-3D239380-26view-3Drev&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=0oGGOb6Hp5KjOM-NE05Xa2gS8lkl1d6kAE-t2drPTA0&s=vu9gKyh-8rePtm0iYu-JmU2boxqZaCVo7bEQEwurl4U&e=>
> Log:
> [DWARF] Fix a few corner cases in expression emission
>
> Summary: I noticed an object file with `DW_OP_reg4 DW_OP_breg4 0` as a DWARF expression,
> which I traced to a missing break (and `++I`) in this code snippet.
> While I was at it, I also added support for a few other corner cases
> along the same lines that I could think of.
>
> Test Plan: Hand-crafted test case to exercises these cases is included.
>
> Reviewers: echristo, dblaikie, aprantl
>
> Reviewed By: aprantl
>
> Subscribers: llvm-commits
>
> Differential Revision: http://reviews.llvm.org/D10302 <https://urldefense.proofpoint.com/v2/url?u=http-3A__reviews.llvm.org_D10302&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=0oGGOb6Hp5KjOM-NE05Xa2gS8lkl1d6kAE-t2drPTA0&s=yN1MPel33JTfhXBC4e6ldkyodavM-6R88DTxQvhIqBU&e=>
>
> Added:
> llvm/trunk/test/DebugInfo/expressions.ll
> Modified:
> llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
> llvm/trunk/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
> llvm/trunk/lib/CodeGen/AsmPrinter/DwarfExpression.h
>
> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp?rev=239380&r1=239379&r2=239380&view=diff <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_lib_CodeGen_AsmPrinter_DwarfDebug.cpp-3Frev-3D239380-26r1-3D239379-26r2-3D239380-26view-3Ddiff&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=0oGGOb6Hp5KjOM-NE05Xa2gS8lkl1d6kAE-t2drPTA0&s=YuDRp23Sd7-JYCkHCeFseKb9puz_1gjB7r6pcdNeWXc&e=>
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp (original)
> +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfDebug.cpp Mon Jun 8 20:53:59 2015
> @@ -1562,6 +1562,8 @@ void DwarfDebug::emitDebugLoc() {
> Asm->OutStreamer->EmitLabel(List.Label);
> const DwarfCompileUnit *CU = List.CU;
> for (const auto &Entry : DebugLocs.getEntries(List)) {
> + if (Entry.BeginSym == Entry.EndSym)
> + continue;
> // Set up the range. This range is relative to the entry point of the
> // compile unit. This is a hard coded 0 for low_pc when we're emitting
> // ranges, or the DW_AT_low_pc on the compile unit otherwise.
>
> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfExpression.cpp?rev=239380&r1=239379&r2=239380&view=diff <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_lib_CodeGen_AsmPrinter_DwarfExpression.cpp-3Frev-3D239380-26r1-3D239379-26r2-3D239380-26view-3Ddiff&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=0oGGOb6Hp5KjOM-NE05Xa2gS8lkl1d6kAE-t2drPTA0&s=yHmJ1JbiHuiDtu3thxi53mXvoHlOkhUS7-aLaOZ8shY&e=>
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfExpression.cpp (original)
> +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfExpression.cpp Mon Jun 8 20:53:59 2015
> @@ -65,6 +65,11 @@ void DwarfExpression::AddShr(unsigned Sh
> EmitOp(dwarf::DW_OP_shr);
> }
>
> +void DwarfExpression::AddOpStackValue() {
> + if (DwarfVersion >= 4)
> + EmitOp(dwarf::DW_OP_stack_value);
> +}
> +
> bool DwarfExpression::AddMachineRegIndirect(unsigned MachineReg, int Offset) {
> if (isFrameRegister(MachineReg)) {
> // If variable offset is based in frame register then use fbreg.
> @@ -172,16 +177,14 @@ void DwarfExpression::AddSignedConstant(
> // value, so the producers and consumers started to rely on heuristics
> // to disambiguate the value vs. location status of the expression.
> // See PR21176 for more details.
> - if (DwarfVersion >= 4)
> - EmitOp(dwarf::DW_OP_stack_value);
> + AddOpStackValue();
> }
>
> void DwarfExpression::AddUnsignedConstant(unsigned Value) {
> EmitOp(dwarf::DW_OP_constu);
> EmitUnsigned(Value);
> // cf. comment in DwarfExpression::AddSignedConstant().
> - if (DwarfVersion >= 4)
> - EmitOp(dwarf::DW_OP_stack_value);
> + AddOpStackValue();
> }
>
> static unsigned getOffsetOrZero(unsigned OffsetInBits,
> @@ -212,15 +215,30 @@ bool DwarfExpression::AddMachineRegExpre
> getOffsetOrZero(OffsetInBits, PieceOffsetInBits));
> }
> case dwarf::DW_OP_plus: {
> - // [DW_OP_reg,Offset,DW_OP_plus,DW_OP_deref] --> [DW_OP_breg,Offset].
> auto N = I.getNext();
> + unsigned Offset = I->getArg(0);
> + // First combine all DW_OP_plus until we hit either a DW_OP_deref or a
> + // DW_OP_bit_piece
> + while (N != E && N->getOp() == dwarf::DW_OP_plus) {
> + Offset += N->getArg(0);
> + ++I;
> + N = I.getNext();
> + }
> if (N != E && N->getOp() == dwarf::DW_OP_deref) {
> - unsigned Offset = I->getArg(0);
> + // [DW_OP_reg,Offset,DW_OP_plus,DW_OP_deref] --> [DW_OP_breg,Offset].
> ValidReg = AddMachineRegIndirect(MachineReg, Offset);
> std::advance(I, 2);
> - break;
> - } else
> - ValidReg = AddMachineRegPiece(MachineReg);
> + } else {
> + assert ((N == E) || (N->getOp() == dwarf::DW_OP_bit_piece));
> + if (Offset == 0) {
> + ValidReg = AddMachineRegPiece(MachineReg);
> + } else {
> + ValidReg = AddMachineRegIndirect(MachineReg, Offset);
> + AddOpStackValue();
> + }
> + ++I;
> + }
> + break;
> }
> case dwarf::DW_OP_deref: {
> // [DW_OP_reg,DW_OP_deref] --> [DW_OP_breg].
> @@ -237,6 +255,7 @@ bool DwarfExpression::AddMachineRegExpre
>
> // Emit remaining elements of the expression.
> AddExpression(I, E, PieceOffsetInBits);
> +
> return true;
> }
>
>
> Modified: llvm/trunk/lib/CodeGen/AsmPrinter/DwarfExpression.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/AsmPrinter/DwarfExpression.h?rev=239380&r1=239379&r2=239380&view=diff <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_lib_CodeGen_AsmPrinter_DwarfExpression.h-3Frev-3D239380-26r1-3D239379-26r2-3D239380-26view-3Ddiff&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=0oGGOb6Hp5KjOM-NE05Xa2gS8lkl1d6kAE-t2drPTA0&s=RajmMxzqJUENxKM33WStiCEGEtcMl9broelcepJ6WJE&e=>
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/AsmPrinter/DwarfExpression.h (original)
> +++ llvm/trunk/lib/CodeGen/AsmPrinter/DwarfExpression.h Mon Jun 8 20:53:59 2015
> @@ -83,6 +83,9 @@ public:
> bool AddMachineRegPiece(unsigned MachineReg, unsigned PieceSizeInBits = 0,
> unsigned PieceOffsetInBits = 0);
>
> + /// Emit a DW_OP_stack_value
> + void AddOpStackValue();
> +
> /// Emit a signed constant.
> void AddSignedConstant(int Value);
> /// Emit an unsigned constant.
>
> Added: llvm/trunk/test/DebugInfo/expressions.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/DebugInfo/expressions.ll?rev=239380&view=auto <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.org_viewvc_llvm-2Dproject_llvm_trunk_test_DebugInfo_expressions.ll-3Frev-3D239380-26view-3Dauto&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=0oGGOb6Hp5KjOM-NE05Xa2gS8lkl1d6kAE-t2drPTA0&s=AH4RF06Nn2OQ7zbwrP0FWzhVQLzT9LWbwYJOs7HD08A&e=>
> ==============================================================================
> --- llvm/trunk/test/DebugInfo/expressions.ll (added)
> +++ llvm/trunk/test/DebugInfo/expressions.ll Mon Jun 8 20:53:59 2015
> @@ -0,0 +1,110 @@
> +; REQUIRES: object-emission
> +; RUN: %llc_dwarf -mtriple x86_64-apple-darwin14.0.0-elf -filetype=obj %s -o %t
> +; RUN: %llc_dwarf -mtriple x86_64-apple-darwin14.0.0-elf -O0 -filetype=obj %s -o %t0
> +; RUN: llvm-dwarfdump -debug-dump=loc %t | FileCheck %s
> +; RUN: llvm-dwarfdump -debug-dump=loc %t0 | FileCheck -check-prefix CHECK-O0 %s
> +
> +; CHECK: 0x00000000: Beginning address offset: 0x0000000000000000
> +; CHECK: Ending address offset: 0x[[END:[0-9a-f]+]]
> +; CHECK: Location description:
> +; CHECK-NOT: 75 00 55
> +; CHECK-SAME: 55
> +; CHECK: 0x00000023: Beginning address offset: 0x0000000000000000
> +; CHECK: Ending address offset: 0x{{.*}}[[END]]
> +; CHECK: Location description: 75 08 9f
> +; CHECK: 0x00000048: Beginning address offset: 0x0000000000000000
> +; CHECK: Ending address offset: 0x{{.*}}[[END]]
> +; CHECK: Location description: 75 10 9f
> +; CHECK: 0x0000006d: Beginning address offset: 0x0000000000000000
> +; CHECK: Ending address offset: 0x{{.*}}[[END]]
> +; CHECK: Location description: 75 18
> +
> +
> +; CHECK-O0: 0x00000000: Beginning address offset: 0x0000000000000000
> +; CHECK-O0: Ending address offset: 0x000000000000001b
> +; CHECK-O0: Location description: 55
> +; CHECK-O0: Beginning address offset: 0x000000000000001b
> +; CHECK-O0: Ending address offset: 0x0000000000000024
> +; CHECK-O0: Location description: 54
> +; CHECK-O0: Beginning address offset: 0x0000000000000024
> +; CHECK-O0: Ending address offset: 0x0000000000000025
> +; CHECK-O0: Location description: 77 78 23 00
> +; CHECK-O0: 0x0000004c: Beginning address offset: 0x0000000000000000
> +; CHECK-O0: Ending address offset: 0x000000000000001b
> +; CHECK-O0: Location description: 75 08 9f
> +; CHECK-O0: Beginning address offset: 0x000000000000001b
> +; CHECK-O0: Ending address offset: 0x0000000000000024
> +; CHECK-O0: Location description: 74 08 9f
> +; CHECK-O0: Beginning address offset: 0x0000000000000024
> +; CHECK-O0: Ending address offset: 0x0000000000000025
> +; CHECK-O0: Location description: 77 78 23 08
> +; CHECK-O0: 0x0000009c: Beginning address offset: 0x0000000000000000
> +; CHECK-O0: Ending address offset: 0x000000000000001b
> +; CHECK-O0: Location description: 75 10 9f
> +; CHECK-O0: Beginning address offset: 0x000000000000001b
> +; CHECK-O0: Ending address offset: 0x0000000000000024
> +; CHECK-O0: Location description: 74 10 9f
> +; CHECK-O0: Beginning address offset: 0x0000000000000024
> +; CHECK-O0: Ending address offset: 0x0000000000000025
> +; CHECK-O0: Location description: 77 78 23 08 23 08
> +; CHECK-O0: 0x000000ee: Beginning address offset: 0x0000000000000000
> +; CHECK-O0: Ending address offset: 0x000000000000001b
> +; CHECK-O0: Location description: 75 18
> +; CHECK-O0: Beginning address offset: 0x000000000000001b
> +; CHECK-O0: Ending address offset: 0x0000000000000024
> +; CHECK-O0: Location description: 74 18
> +; CHECK-O0: Beginning address offset: 0x0000000000000024
> +; CHECK-O0: Ending address offset: 0x0000000000000025
> +; CHECK-O0: Location description: 77 78 23 10 23 08 06
> +
> +declare void @llvm.dbg.value(metadata, i64, metadata, metadata) #0
> +
> +define float @foo(float* %args, float *%args2)
> +{
> + call void @llvm.dbg.value(metadata float* %args, i64 0, metadata !11, metadata !12), !dbg !19
> + call void @llvm.dbg.value(metadata float* %args, i64 0, metadata !13, metadata !14), !dbg !19
> + call void @llvm.dbg.value(metadata float* %args, i64 0, metadata !15, metadata !16), !dbg !19
> + call void @llvm.dbg.value(metadata float* %args, i64 0, metadata !17, metadata !18), !dbg !19
> + %a = load float, float* %args, !dbg !19
> + %bptr = getelementptr float, float* %args, i32 1, !dbg !19
> + %b = load float, float* %bptr, !dbg !19
> + %cptr = getelementptr float, float* %args, i32 2, !dbg !19
> + %c = load float, float* %cptr, !dbg !19
> + %dptr = getelementptr float, float* %args, i32 3, !dbg !19
> + %d = load float, float* %dptr, !dbg !19
> + %ret1 = fadd float %a, %b, !dbg !19
> + %ret2 = fadd float %c, %d, !dbg !19
> + call void @llvm.dbg.value(metadata float* %args2, i64 0, metadata !11, metadata !12), !dbg !19
> + call void @llvm.dbg.value(metadata float* %args2, i64 0, metadata !13, metadata !14), !dbg !19
> + call void @llvm.dbg.value(metadata float* %args2, i64 0, metadata !15, metadata !16), !dbg !19
> + call void @llvm.dbg.value(metadata float* %args2, i64 0, metadata !17, metadata !18), !dbg !19
> + %ret = fsub float %ret1, %ret2, !dbg !19
> + ret float %ret, !dbg !19
> +}
> +
> +attributes #0 = { nounwind readnone }
> +
> +!llvm.module.flags = !{!0, !1}
> +!llvm.dbg.cu <https://urldefense.proofpoint.com/v2/url?u=http-3A__llvm.dbg.cu&d=AwMFaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=mQ4LZ2PUj9hpadE3cDHZnIdEwhEBrbAstXeMaFoB9tg&m=0oGGOb6Hp5KjOM-NE05Xa2gS8lkl1d6kAE-t2drPTA0&s=0O149Lfck9oiYPzb4rRQC0eNFvJwnhYBQHneqGH2gHQ&e=> = !{!2}
> +
> +!0 = !{i32 2, !"Dwarf Version", i32 4}
> +!1 = !{i32 1, !"Debug Info Version", i32 3}
> +
> +!2 = !DICompileUnit(language: DW_LANG_C89, file: !3, producer: "byHand", isOptimized: true, runtimeVersion: 0, emissionKind: 1, enums: !4, retainedTypes: !4, subprograms: !5, globals: !4, imports: !4)
> +!3 = !DIFile(filename: "expressions", directory: ".")
> +!4 = !{}
> +!5 = !{!6}
> +!6 = !DISubprogram(name: "foo", linkageName: "foo", scope: null, file: !3, type: !7, isLocal: false, isDefinition: true, isOptimized: true, function: float (float*, float*)* @foo, variables: !4)
> +!7 = !DISubroutineType(types: !8)
> +!8 = !{!10, !10}
> +!9 = !DIBasicType(name: "float", size: 4, align: 4, encoding: DW_ATE_float)
> +!10 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: !9, size: 64, align: 64)
> +!11 = !DILocalVariable(tag: DW_TAG_arg_variable, name: "a", arg: 1, scope: !6, file: !3, line: 1, type: !10)
> +!12 = !DIExpression(DW_OP_plus, 0)
> +!13 = !DILocalVariable(tag: DW_TAG_arg_variable, name: "b", arg: 2, scope: !6, file: !3, line: 1, type: !10)
> +!14 = !DIExpression(DW_OP_plus, 8)
> +!15 = !DILocalVariable(tag: DW_TAG_arg_variable, name: "c", arg: 3, scope: !6, file: !3, line: 1, type: !10)
> +!16 = !DIExpression(DW_OP_plus, 8, DW_OP_plus, 8)
> +!17 = !DILocalVariable(tag: DW_TAG_arg_variable, name: "d", arg: 4, scope: !6, file: !3, line: 1, type: !9)
> +!18 = !DIExpression(DW_OP_plus, 16, DW_OP_plus, 8, DW_OP_deref)
> +!19 = !DILocation(line: 1, scope: !6)
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at cs.uiuc.edu <mailto:llvm-commits at cs.uiuc.edu>
> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits <http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits>
>
>
>
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20150611/96a1e70d/attachment.html>
More information about the llvm-commits
mailing list