MC: force eager evaluation of relocations in .debug_info

Force eager evaluation of symbolic difference on debug_info which is
required to be resolved eagerly for fission as dwo sections may not
contain relocations.

Fixes: llvm#56642

Author: compnerd

llvm/lib/MC/MCObjectStreamer.cpp

@@ -162,15 +162,17 @@ static Optional<uint64_t> absoluteSymbolDiff(const MCSymbol *Hi,
 void MCObjectStreamer::emitAbsoluteSymbolDiff(const MCSymbol *Hi,
                                               const MCSymbol *Lo,
                                               unsigned Size) {
-  if (!getAssembler().getContext().getTargetTriple().isRISCV())
+  if (!getAssembler().getContext().getTargetTriple().isRISCV() ||
+      getCurrentFragment()->getParent()->getName().startswith(".debug_info"))
     if (Optional<uint64_t> Diff = absoluteSymbolDiff(Hi, Lo))
       return emitIntValue(*Diff, Size);
   MCStreamer::emitAbsoluteSymbolDiff(Hi, Lo, Size);
 }
 
 void MCObjectStreamer::emitAbsoluteSymbolDiffAsULEB128(const MCSymbol *Hi,
                                                        const MCSymbol *Lo) {
-  if (!getAssembler().getContext().getTargetTriple().isRISCV())
+  if (!getAssembler().getContext().getTargetTriple().isRISCV() ||
+      getCurrentFragment()->getParent()->getName().startswith(".debug_info"))
     if (Optional<uint64_t> Diff = absoluteSymbolDiff(Hi, Lo))
       return emitULEB128IntValue(*Diff);
   MCStreamer::emitAbsoluteSymbolDiffAsULEB128(Hi, Lo);

llvm/test/CodeGen/RISCV/fixups-diff.ll

@@ -23,10 +23,8 @@ entry:
 }
 
 ; CHECK:      Section {{.*}} .rela.debug_info {
-; CHECK:        0x22 R_RISCV_ADD32 - 0x0
-; CHECK-NEXT:   0x22 R_RISCV_SUB32 - 0x0
-; CHECK:        0x2B R_RISCV_ADD32 - 0x0
-; CHECK-NEXT:   0x2B R_RISCV_SUB32 - 0x0
+; CHECK:        0x27 R_RISCV_32 - 0x0
+; CHECK:        0x31 R_RISCV_32 - 0x0
 ; CHECK:      }
 
 ; CHECK:      Section {{.*}} .rela.eh_frame {

llvm/test/DebugInfo/RISCV/debug_info.ll

@@ -0,0 +1,41 @@
+; RUN: llc -mtriple riscv64-unknown-linux-gnu -filetype obj %s -o - | llvm-dwarfdump - | FileCheck %s -check-prefix CHECK-DWARF
+; RUN: llc -mtriple riscv64-unknown-linux-gnu -filetype obj %s -o - | llvm-readobj -r - | FileCheck %s -check-prefix CHECK-OBJ
+
+source_filename = "reduced.c"
+target datalayout = "e-m:e-p:64:64-i64:64-i128:128-n64-S128"
+target triple = "riscv64-unknown-linux-gnu"
+
+define dso_local signext i32 @f() #0 !dbg !7 {
+entry:
+  ret i32 32, !dbg !13
+}
+
+attributes #0 = { noinline nounwind optnone "frame-pointer"="none" "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-features"="+64bit" }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!2, !3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 15.0.0", isOptimized: false, runtimeVersion: 0, splitDebugFilename: "reduced.dwo", emissionKind: FullDebug, splitDebugInlining: false, nameTableKind: None)
+!1 = !DIFile(filename: "reduced.c", directory: "/SourceCache")
+!2 = !{i32 2, !"Debug Info Version", i32 3}
+!3 = !{i32 1, !"wchar_size", i32 4}
+!4 = !{i32 1, !"target-abi", !"lp64"}
+!5 = !{i32 1, !"SmallDataLimit", i32 0}
+!6 = !{!"clang version 15.0.0"}
+!7 = distinct !DISubprogram(name: "f", scope: !8, file: !8, line: 2, type: !9, scopeLine: 2, flags: DIFlagPrototyped, spFlags: DISPFlagDefinition, unit: !0, retainedNodes: !12)
+!8 = !DIFile(filename: "/SourceCache/reduced.c", directory: "")
+!9 = !DISubroutineType(types: !10)
+!10 = !{!11}
+!11 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!12 = !{}
+!13 = !DILocation(line: 2, column: 15, scope: !7)
+
+; CHECK-DWARF:      0x0000002a:   DW_TAG_subprogram
+; CHECK-DWARF-NEXT:                 DW_AT_low_pc	(0x0000000000000000)
+; CHECK-DWARF-NEXT:                 DW_AT_high_pc	(0x0000000000000008)
+
+; CHECK-OBJ: Section (5) .rela.debug_info {
+; CHECK-OBJ:       0x1A R_RISCV_32 - 0x0
+; CHECK-OBJ:       0x1E R_RISCV_64 - 0x0
+; CHECK-OBJ: }

llvm/test/DebugInfo/RISCV/dwarf-riscv-relocs.ll

@@ -6,8 +6,7 @@
 
 ; Check that we actually have relocations, otherwise this is kind of pointless.
 ; READOBJ-RELOCS:  Section ({{.*}}) .rela.debug_info {
-; READOBJ-RELOCS:    0x1B R_RISCV_ADD32 - 0x0
-; READOBJ-RELOCS-NEXT:    0x1B R_RISCV_SUB32 - 0x0
+; READOBJ-RELOCS:    0x11 R_RISCV_32 - 0x0
 ; READOBJ-RELOCS:  Section ({{.*}}) .rela.debug_frame {
 ; READOBJ-RELOCS:    0x20 R_RISCV_ADD32 - 0x0
 ; READOBJ-RELOCS-NEXT:    0x20 R_RISCV_SUB32 - 0x0