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[DebugInfo] Add DW_OP_LLVM_extract_bits #93990

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Merged
merged 4 commits into from
Jun 7, 2024
Merged

[DebugInfo] Add DW_OP_LLVM_extract_bits #93990

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7b0ac40
[DebugInfo] Add DW_OP_LLVM_extract_bits
john-brawn-arm May 29, 2024
7dab730
Remove some unnecessary debug metadata in test
john-brawn-arm Jun 3, 2024
083dc52
Put sign information in the opcode instead of as an operand.
john-brawn-arm Jun 6, 2024
342011f
Use regex in tests
john-brawn-arm Jun 6, 2024
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7 changes: 7 additions & 0 deletions llvm/docs/LangRef.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -6312,6 +6312,13 @@ The current supported opcode vocabulary is limited:
(``16`` and ``DW_ATE_signed`` here, respectively) to which the top of the
expression stack is to be converted. Maps into a ``DW_OP_convert`` operation
that references a base type constructed from the supplied values.
- ``DW_OP_LLVM_extract_bits, 16, 8, DW_ATE_signed`` specifies the offset, size,
and encoding (``16``, ``8``, and ``DW_ATE_signed`` here, respectively) of bits
that are to be extracted from the value at the top of the expression stack.
If the top of the expression stack is a memory location then these bits are
extracted from the value pointed to by that memory location. Maps into a
``DW_OP_shl`` followed by ``DW_OP_shr`` or ``DW_OP_shra`` (depending on
encoding).
- ``DW_OP_LLVM_tag_offset, tag_offset`` specifies that a memory tag should be
optionally applied to the pointer. The memory tag is derived from the
given tag offset in an implementation-defined manner.
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1 change: 1 addition & 0 deletions llvm/include/llvm/BinaryFormat/Dwarf.h
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Expand Up @@ -144,6 +144,7 @@ enum LocationAtom {
DW_OP_LLVM_entry_value = 0x1003, ///< Only used in LLVM metadata.
DW_OP_LLVM_implicit_pointer = 0x1004, ///< Only used in LLVM metadata.
DW_OP_LLVM_arg = 0x1005, ///< Only used in LLVM metadata.
DW_OP_LLVM_extract_bits = 0x1006, ///< Only used in LLVM metadata.
};

enum LlvmUserLocationAtom {
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3 changes: 3 additions & 0 deletions llvm/lib/BinaryFormat/Dwarf.cpp
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Expand Up @@ -155,6 +155,8 @@ StringRef llvm::dwarf::OperationEncodingString(unsigned Encoding) {
return "DW_OP_LLVM_implicit_pointer";
case DW_OP_LLVM_arg:
return "DW_OP_LLVM_arg";
case DW_OP_LLVM_extract_bits:
return "DW_OP_LLVM_extract_bits";
}
}

Expand All @@ -169,6 +171,7 @@ unsigned llvm::dwarf::getOperationEncoding(StringRef OperationEncodingString) {
.Case("DW_OP_LLVM_entry_value", DW_OP_LLVM_entry_value)
.Case("DW_OP_LLVM_implicit_pointer", DW_OP_LLVM_implicit_pointer)
.Case("DW_OP_LLVM_arg", DW_OP_LLVM_arg)
.Case("DW_OP_LLVM_extract_bits", DW_OP_LLVM_extract_bits)
.Default(0);
}

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32 changes: 32 additions & 0 deletions llvm/lib/CodeGen/AsmPrinter/DwarfExpression.cpp
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Expand Up @@ -18,6 +18,7 @@
#include "llvm/CodeGen/Register.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/MC/MCAsmInfo.h"
#include "llvm/Support/ErrorHandling.h"
#include <algorithm>

Expand Down Expand Up @@ -546,6 +547,37 @@ bool DwarfExpression::addExpression(
LocationKind = Unknown;
return true;
}
case dwarf::DW_OP_LLVM_extract_bits: {
unsigned SizeInBits = Op->getArg(1);
unsigned BitOffset = Op->getArg(0);
dwarf::TypeKind Encoding = static_cast<dwarf::TypeKind>(Op->getArg(2));

// If we have a memory location then dereference to get the value
if (isMemoryLocation())
emitOp(dwarf::DW_OP_deref);

// Extract the bits by a shift left (to shift out the bits after what we
// want to extract) followed by shift right (to shift the bits to position
// 0 and also sign/zero extend). These operations are done in the DWARF
// "generic type" whose size is the size of a pointer.
unsigned PtrSizeInBytes = CU.getAsmPrinter()->MAI->getCodePointerSize();
unsigned LeftShift = PtrSizeInBytes * 8 - (SizeInBits + BitOffset);
unsigned RightShift = LeftShift + BitOffset;
if (LeftShift) {
emitOp(dwarf::DW_OP_constu);
emitUnsigned(LeftShift);
emitOp(dwarf::DW_OP_shl);
}
emitOp(dwarf::DW_OP_constu);
emitUnsigned(RightShift);
emitOp(Encoding == dwarf::DW_ATE_signed ? dwarf::DW_OP_shra
: dwarf::DW_OP_shr);

// The value is now at the top of the stack, so set the location to
// implicit so that we get a stack_value at the end.
LocationKind = Implicit;
break;
}
case dwarf::DW_OP_plus_uconst:
assert(!isRegisterLocation());
emitOp(dwarf::DW_OP_plus_uconst);
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4 changes: 4 additions & 0 deletions llvm/lib/IR/AsmWriter.cpp
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Expand Up @@ -2468,6 +2468,10 @@ static void writeDIExpression(raw_ostream &Out, const DIExpression *N,
if (Op.getOp() == dwarf::DW_OP_LLVM_convert) {
Out << FS << Op.getArg(0);
Out << FS << dwarf::AttributeEncodingString(Op.getArg(1));
} else if (Op.getOp() == dwarf::DW_OP_LLVM_extract_bits) {
Out << FS << Op.getArg(0);
Out << FS << Op.getArg(1);
Out << FS << dwarf::AttributeEncodingString(Op.getArg(2));
} else {
for (unsigned A = 0, AE = Op.getNumArgs(); A != AE; ++A)
Out << FS << Op.getArg(A);
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3 changes: 3 additions & 0 deletions llvm/lib/IR/DebugInfoMetadata.cpp
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Expand Up @@ -1402,6 +1402,8 @@ unsigned DIExpression::ExprOperand::getSize() const {
return 2;

switch (Op) {
case dwarf::DW_OP_LLVM_extract_bits:
return 4;
case dwarf::DW_OP_LLVM_convert:
case dwarf::DW_OP_LLVM_fragment:
case dwarf::DW_OP_bregx:
Expand Down Expand Up @@ -1474,6 +1476,7 @@ bool DIExpression::isValid() const {
case dwarf::DW_OP_LLVM_convert:
case dwarf::DW_OP_LLVM_arg:
case dwarf::DW_OP_LLVM_tag_offset:
case dwarf::DW_OP_LLVM_extract_bits:
case dwarf::DW_OP_constu:
case dwarf::DW_OP_plus_uconst:
case dwarf::DW_OP_plus:
Expand Down
99 changes: 99 additions & 0 deletions llvm/test/DebugInfo/X86/DW_OP_LLVM_extract_bits.ll
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@@ -0,0 +1,99 @@
; RUN: llc -mtriple=x86_64-unknown-linux-gnu %s -o %t -filetype=obj
; RUN: llvm-dwarfdump --debug-info %t | FileCheck %s

%struct.struct_t = type { i8 }

@g = dso_local global %struct.struct_t zeroinitializer, align 1, !dbg !0

; CHECK-LABEL: DW_TAG_subprogram
; CHECK: DW_AT_name ("test1")
; CHECK: DW_TAG_variable
; CHECK: DW_AT_location (DW_OP_fbreg -1, DW_OP_deref, DW_OP_constu 0x3d, DW_OP_shl, DW_OP_constu 0x3d, DW_OP_shr, DW_OP_stack_value)
; CHECK: DW_AT_name ("x")
; CHECK: DW_TAG_variable
; CHECK: DW_AT_location (DW_OP_fbreg -1, DW_OP_deref, DW_OP_constu 0x39, DW_OP_shl, DW_OP_constu 0x3c, DW_OP_shra, DW_OP_stack_value)
; CHECK: DW_AT_name ("y")

define i32 @test1() !dbg !13 {
entry:
%0 = alloca %struct.struct_t, align 1
tail call void @llvm.dbg.declare(metadata ptr %0, metadata !17, metadata !DIExpression(DW_OP_LLVM_extract_bits, 0, 3, DW_ATE_unsigned)), !dbg !18
tail call void @llvm.dbg.declare(metadata ptr %0, metadata !19, metadata !DIExpression(DW_OP_LLVM_extract_bits, 3, 4, DW_ATE_signed)), !dbg !21
ret i32 0, !dbg !22
}

; CHECK-LABEL: DW_TAG_subprogram
; CHECK: DW_AT_name ("test2")
; CHECK: DW_TAG_variable
; CHECK: DW_AT_location (DW_OP_breg0 RAX+0, DW_OP_constu 0xff, DW_OP_and, DW_OP_constu 0x3d, DW_OP_shl, DW_OP_constu 0x3d, DW_OP_shr, DW_OP_stack_value)
; CHECK: DW_AT_name ("x")
; CHECK: DW_TAG_variable
; CHECK: DW_AT_location (DW_OP_breg0 RAX+0, DW_OP_constu 0xff, DW_OP_and, DW_OP_constu 0x39, DW_OP_shl, DW_OP_constu 0x3c, DW_OP_shra, DW_OP_stack_value)
; CHECK: DW_AT_name ("y")

define i8 @test2() !dbg !23 {
entry:
%0 = load i8, ptr @g, align 1
tail call void @llvm.dbg.value(metadata i8 %0, metadata !24, metadata !DIExpression(DW_OP_LLVM_extract_bits, 0, 3, DW_ATE_unsigned)), !dbg !25
tail call void @llvm.dbg.value(metadata i8 %0, metadata !26, metadata !DIExpression(DW_OP_LLVM_extract_bits, 3, 4, DW_ATE_signed)), !dbg !27
ret i8 %0, !dbg !28
}

; CHECK-LABEL: DW_TAG_subprogram
; CHECK: DW_AT_name ("test3")
; CHECK: DW_TAG_variable
; CHECK: DW_AT_location (DW_OP_breg0 RAX+0, DW_OP_constu 0x3f, DW_OP_shr, DW_OP_stack_value)
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This test seems to hardcode some register allocation assumptions. What do you think about converting it to MIR?

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It looks like MIR doesn't handle multiple debug values in the same stack location. The MIR generated for test1 (by running DW_OP_LLVM_extract_bits.ll through llc with --stop-after=patchable-function) has

stack:
  - { id: 0, name: '', type: default, offset: -9, size: 1, alignment: 1,
      stack-id: default, callee-saved-register: '', callee-saved-restored: true,
      debug-info-variable: '!17!19', debug-info-expression: '!DIExpression(DW_OP_LLVM_extract_bits, 0, 3, DW_ATE_unsigned)!DIExpression(DW_OP_LLVM_extract_bits, 3, 4, DW_ATE_signed)',
      debug-info-location: '!18!21' }

which llc then gives an error for on reading it:

error: tmp.mir:130:32: expected end of string after the metadata node
      debug-info-variable: '!17!19', debug-info-expression: '!DIExpression(DW_OP_LLVM_extract_bits, 0, 3, DW_ATE_unsigned)!DIExpression(DW_OP_LLVM_extract_bits, 3, 4, DW_ATE_signed)',
                               ^

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Hm, this is a silly bug - I remember seeing it some time ago, I thought it had been fixed! This isn't a technical limitation of MIR in-memory, but an error in how it is printed (and possibly parsed) that should be fixed soon; I'll take a look at it soon. In the meanwhile, you could use regex (something like {{R[^+]+}}?) to match any 64 bit register.

; CHECK: DW_AT_name ("x")
; CHECK: DW_TAG_variable
; CHECK: DW_AT_location (DW_OP_breg0 RAX+0, DW_OP_constu 0x3f, DW_OP_shra, DW_OP_stack_value)
; CHECK: DW_AT_name ("y")

define i64 @test3(ptr %p) !dbg !29 {
entry:
%0 = load i64, ptr %p, align 8
tail call void @llvm.dbg.value(metadata i64 %0, metadata !33, metadata !DIExpression(DW_OP_LLVM_extract_bits, 63, 1, DW_ATE_unsigned)), !dbg !30
tail call void @llvm.dbg.value(metadata i64 %0, metadata !34, metadata !DIExpression(DW_OP_LLVM_extract_bits, 63, 1, DW_ATE_signed)), !dbg !31
ret i64 %0, !dbg !32
}

declare void @llvm.dbg.declare(metadata, metadata, metadata)
declare void @llvm.dbg.value(metadata, metadata, metadata)

!llvm.dbg.cu = !{!2}
!llvm.module.flags = !{!11, !12}

!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
!1 = distinct !DIGlobalVariable(name: "g", scope: !2, file: !3, line: 6, type: !5, isLocal: false, isDefinition: true)
!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus_14, file: !3, isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, globals: !4, splitDebugInlining: false, nameTableKind: None)
!3 = !DIFile(filename: "DW_OP_bit_piece.cpp", directory: "./")
!4 = !{!0}
!5 = !DIDerivedType(tag: DW_TAG_typedef, name: "struct_t", file: !3, line: 4, baseType: !6)
!6 = distinct !DICompositeType(tag: DW_TAG_structure_type, file: !3, line: 1, size: 8, flags: DIFlagTypePassByValue, elements: !7, identifier: "_ZTS8struct_t")
!7 = !{!8, !10}
!8 = !DIDerivedType(tag: DW_TAG_member, name: "x", scope: !6, file: !3, line: 2, baseType: !9, size: 3, flags: DIFlagBitField, extraData: i64 0)
!9 = !DIBasicType(name: "unsigned int", size: 32, encoding: DW_ATE_unsigned)
!10 = !DIDerivedType(tag: DW_TAG_member, name: "y", scope: !6, file: !3, line: 3, baseType: !9, size: 4, offset: 3, flags: DIFlagBitField, extraData: i64 0)
!11 = !{i32 7, !"Dwarf Version", i32 5}
!12 = !{i32 2, !"Debug Info Version", i32 3}
!13 = distinct !DISubprogram(name: "test1", linkageName: "test1", scope: !3, file: !3, line: 8, type: !14, scopeLine: 8, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !16)
!14 = !DISubroutineType(types: !15)
!15 = !{!9}
!16 = !{}
!17 = !DILocalVariable(name: "x", scope: !13, file: !3, line: 9, type: !9)
!18 = !DILocation(line: 9, column: 9, scope: !13)
!19 = !DILocalVariable(name: "y", scope: !13, file: !3, line: 9, type: !20)
!20 = !DIBasicType(name: "signed int", size: 32, encoding: DW_ATE_signed)
!21 = !DILocation(line: 9, column: 12, scope: !13)
!22 = !DILocation(line: 10, column: 3, scope: !13)
!23 = distinct !DISubprogram(name: "test2", linkageName: "test2", scope: !3, file: !3, line: 8, type: !14, scopeLine: 8, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !16)
!24 = !DILocalVariable(name: "x", scope: !23, file: !3, line: 9, type: !9)
!25 = !DILocation(line: 9, column: 9, scope: !23)
!26 = !DILocalVariable(name: "y", scope: !23, file: !3, line: 9, type: !20)
!27 = !DILocation(line: 9, column: 12, scope: !23)
!28 = !DILocation(line: 10, column: 3, scope: !23)
!29 = distinct !DISubprogram(name: "test3", linkageName: "test3", scope: !3, file: !3, line: 8, type: !14, scopeLine: 8, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !2, retainedNodes: !16)
!30 = !DILocation(line: 9, column: 9, scope: !29)
!31 = !DILocation(line: 9, column: 12, scope: !29)
!32 = !DILocation(line: 10, column: 3, scope: !29)
!33 = !DILocalVariable(name: "x", scope: !29, file: !3, line: 9, type: !9)
!34 = !DILocalVariable(name: "y", scope: !29, file: !3, line: 9, type: !20)