[DebugInfo] Handle generic type DW_OP_convert ops in dsymutil

[dstenb]

Summary

This is a preparatory change for allowing LLVM to emit DW_OP_convert
operations converting to the generic type.

If DW_OP_convert's operand is 0, it converts the top of the stack to the
generic type, as specified by DWARFv5 section 2.5.1.6:

"[...] takes one operand, which is an unsigned LEB128 integer that
represents the offset of a debugging information entry in the current
compilation unit, or value 0 which represents the generic type."

This adds support for such operations to dsymutil.

I have no knowledge of dsymutil, so I have been guided in the dark by
completely by D58534.

[aprantl]

Thanks!

[dstenb]

Remove binary file from diff due to issues with arc patch. I'll add the file back when landing this, which I plan to do shortly.

llvm/lib/DWARFLinker/DWARFLinker.cpp

if ((Op0 == Encoding::BaseTypeRef && Op1 == Encoding::SizeNA) ||
       OutputBuffer.push_back(Op.getCode());
       uint64_t RefOffset;
       if (Op1 == Encoding::SizeNA) {
         RefOffset = Op.getRawOperand(0);
       } else {
         OutputBuffer.push_back(Op.getRawOperand(0));
         RefOffset = Op.getRawOperand(1);
       }
+      uint32_t Offset = 0;
+      // Look up the base type. For DW_OP_convert, the operand may be 0 to
+      // instead indicate the generic type. The same holds for
+      // DW_OP_reinterpret, which is currently not supported.
+      if (RefOffset > 0 || Op.getCode() != dwarf::DW_OP_convert) {
         auto RefDie = Unit.getOrigUnit().getDIEForOffset(RefOffset);
         uint32_t RefIdx = Unit.getOrigUnit().getDIEIndex(RefDie);
         CompileUnit::DIEInfo &Info = Unit.getInfo(RefIdx);
-      uint32_t Offset = 0;
         if (DIE *Clone = Info.Clone)
           Offset = Clone->getOffset();
         else
-        Linker.reportWarning("base type ref doesn't point to DW_TAG_base_type.",
-                             File);
+          Linker.reportWarning(
+              "base type ref doesn't point to DW_TAG_base_type.", File);
+      }
       uint8_t ULEB[16];
       unsigned RealSize = encodeULEB128(Offset, ULEB, ULEBsize);
       if (RealSize > ULEBsize) {
         // Emit the generic type as a fallback.
         RealSize = encodeULEB128(0, ULEB, ULEBsize);
         Linker.reportWarning("base type ref doesn't fit.", File);
       }
       assert(RealSize == ULEBsize && "padding failed");

llvm/test/tools/dsymutil/Inputs/op-convert.ll

 ; ModuleID = 'dbg.ll'
 source_filename = "dbg.c"
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
 target triple = "x86_64-apple-macosx"
 
 ; Function Attrs: noinline nounwind uwtable
 define signext i8 @foo(i8 signext %x) #0 !dbg !7 {
 entry:
   call void @llvm.dbg.value(metadata i8 42, metadata !17, metadata !DIExpression(DW_OP_LLVM_convert, 32, DW_ATE_signed, DW_OP_stack_value)), !dbg !12
   call void @llvm.dbg.value(metadata i8 %x, metadata !11, metadata !DIExpression()), !dbg !12
   call void @llvm.dbg.value(metadata i8 %x, metadata !13, metadata !DIExpression(DW_OP_LLVM_convert, 8, DW_ATE_signed, DW_OP_LLVM_convert, 32, DW_ATE_signed, DW_OP_stack_value)), !dbg !15
+  call void @llvm.dbg.value(metadata i8 51, metadata !18, metadata !DIExpression(DW_OP_LLVM_convert_generic, DW_OP_stack_value)), !dbg !15
   ret i8 %x, !dbg !16
 }
 
 ; Function Attrs: nounwind readnone speculatable
 declare void @llvm.dbg.declare(metadata, metadata, metadata) #1
 
 ; Function Attrs: nounwind readnone speculatable
 declare void @llvm.dbg.value(metadata, metadata, metadata) #1

 !10 = !DIBasicType(name: "signed char", size: 8, encoding: DW_ATE_signed_char)
 !11 = !DILocalVariable(name: "x", arg: 1, scope: !7, file: !1, line: 1, type: !10)
 !12 = !DILocation(line: 1, column: 29, scope: !7)
 !13 = !DILocalVariable(name: "y", scope: !7, file: !1, line: 3, type: !14)
 !14 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
 !15 = !DILocation(line: 3, column: 14, scope: !7)
 !16 = !DILocation(line: 4, column: 3, scope: !7)
 !17 = !DILocalVariable(name: "c", scope: !7, file: !1, line: 3, type: !14)
+!18 = !DILocalVariable(name: "d", scope: !7, file: !1, line: 3, type: !14)

llvm/test/tools/dsymutil/X86/op-convert.test

 
 CHECK:     DW_TAG_variable
 CHECK-NEXT:     DW_AT_location  (
 CHECK-NEXT:     [0x0000000000001000,  0x0000000000001002): DW_OP_breg5 RDI+0, DW_OP_constu 0xffffffff, DW_OP_and, DW_OP_convert (0x0000002a) "DW_ATE_signed_8", DW_OP_convert (0x00000031) "DW_ATE_signed_32", DW_OP_stack_value
 CHECK-NEXT:     [0x0000000000001002,  0x0000000000001003): DW_OP_breg0 RAX+0, DW_OP_constu 0xffffffff, DW_OP_and, DW_OP_convert (0x0000002a) "DW_ATE_signed_8", DW_OP_convert (0x00000031) "DW_ATE_signed_32", DW_OP_stack_value)
 CHECK-NEXT:     DW_AT_name  ("y")
 
 CHECK:     DW_TAG_variable
+CHECK-NEXT:     DW_AT_location  (DW_OP_constu 0x33, DW_OP_convert 0x0, DW_OP_stack_value)
+CHECK-NEXT:     DW_AT_name  ("d")
+
+CHECK:     DW_TAG_variable
 CHECK-NEXT:     DW_AT_location  (DW_OP_constu 0x2a, DW_OP_convert (0x00000031) "DW_ATE_signed_32", DW_OP_stack_value)
 CHECK-NEXT:     DW_AT_name  ("c")