[DebugInfo] Emit comments for debug_loc bytes as integers

[dstenb]

Summary

The DebugLocDwarfExpression::emitData1() function would emit the
assembly file comments using raw characters. As emitting non-printable
characters or characters >127 can lead to issues, just emit the comments
as integers instead.

[dblaikie]

Perhaps we shouldn't use a comment here? It doesn't seem to add any value - duplicating the literal that's already readable. (ideally we could pass down a comment from a higher level with more semantic information - like the DW_OP_implicit_value comment.

I'd say removing this Twine creation, passing down an empty string would suffice here. If you'd like to add value/maybe in a separate commit, adding an optional Comment parameter to emitUnsigned and emitData1 and using that from in this case DwarfExpression::addConstantFP to pass down something like emitUnsigned(NumBytes, ) and then maybe on the first call to emitData1 a comment with the APF and the original (unswapped) API values, and some text saying that this is the start of a ULEB encoding of the API value, LSB first.

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

void DebugLocDwarfExpression::emitSigned(int64_t Value) {
   getActiveStreamer().emitSLEB128(Value, Twine(Value));
 }
 
 void DebugLocDwarfExpression::emitUnsigned(uint64_t Value) {
   getActiveStreamer().emitULEB128(Value, Twine(Value));
 }
 
 void DebugLocDwarfExpression::emitData1(uint8_t Value) {
-  getActiveStreamer().emitInt8(Value, Twine(Value));
+  getActiveStreamer().emitInt8(Value, Twine((int)Value));
 }
 
 void DebugLocDwarfExpression::emitBaseTypeRef(uint64_t Idx) {
   assert(Idx < (1ULL << (ULEB128PadSize * 7)) && "Idx wont fit");
   getActiveStreamer().emitULEB128(Idx, Twine(Idx), ULEB128PadSize);
 }
 
 bool DebugLocDwarfExpression::isFrameRegister(const TargetRegisterInfo &TRI,

llvm/test/DebugInfo/X86/implicit_value_comments.ll

+;; This test verifies that the comments for the bytes in the
+;; DW_OP_implicit_value operation are emitted as integers rather than
+;; characters.
+
+; RUN: llc -debugger-tune=gdb -filetype=asm %s -o -  | FileCheck %s
+
+; CHECK: .short  6                               # Loc expr size
+; CHECK-NEXT: .byte   158                        # DW_OP_implicit_value
+; CHECK-NEXT: .byte   4                          # 4
+; CHECK-NEXT: .byte   195                        # 195
+; CHECK-NEXT: .byte   245                        # 245
+; CHECK-NEXT: .byte   72                         # 72
+; CHECK-NEXT: .byte   64                         # 64
+; CHECK-NEXT: .quad   0
+; CHECK-NEXT: .quad   0
+
+;; Generated from: clang -ggdb -O1
+;;int main() {
+;;        float f = 3.14f;
+;;        printf("dummy\n");
+;;        f *= f;
+;;        return 0;
+;;}
+; ModuleID = 'implicit_value_comments.c'
+source_filename = "implicit_value_comments.c"
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@str = private unnamed_addr constant [6 x i8] c"dummy\00", align 1
+
+; Function Attrs: nofree nounwind uwtable
+define dso_local i32 @main() local_unnamed_addr #0 !dbg !7 {
+entry:
+  call void @llvm.dbg.value(metadata float 0x40091EB860000000, metadata !12, metadata !DIExpression()), !dbg !14
+  %puts = call i32 @puts(i8* nonnull dereferenceable(1) getelementptr inbounds ([6 x i8], [6 x i8]* @str, i64 0, i64 0)), !dbg !15
+  call void @llvm.dbg.value(metadata float undef, metadata !12, metadata !DIExpression()), !dbg !14
+  ret i32 0, !dbg !16
+}
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare void @llvm.dbg.value(metadata, metadata, metadata) #1
+
+; Function Attrs: nofree nounwind
+declare i32 @puts(i8* nocapture readonly) local_unnamed_addr #2
+
+attributes #0 = { nofree nounwind uwtable }
+attributes #1 = { nounwind readnone speculatable willreturn }
+attributes #2 = { nofree nounwind }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 11.0.0", isOptimized: true, runtimeVersion: 0, emissionKind: FullDebug, enums: !2, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "implicit_value_comments.c", directory: "/home/")
+!2 = !{}
+!3 = !{i32 7, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 11.0.0"}
+!7 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 1, type: !8, scopeLine: 1, flags: DIFlagAllCallsDescribed, spFlags: DISPFlagDefinition | DISPFlagOptimized, unit: !0, retainedNodes: !11)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !{!12}
+!12 = !DILocalVariable(name: "f", scope: !7, file: !1, line: 2, type: !13)
+!13 = !DIBasicType(name: "float", size: 32, encoding: DW_ATE_float)
+!14 = !DILocation(line: 0, scope: !7)
+!15 = !DILocation(line: 3, column: 2, scope: !7)
+!16 = !DILocation(line: 5, column: 2, scope: !7)