[WebAssembly] Add support for DWARF type units

Since Wasm comdat sections work similarly to ELF, we can use that mechanism
to eliminate duplicate dwarf type information in the same way.

Differential Revision: https://reviews.llvm.org/D88603

clang/lib/Driver/ToolChains/Clang.cpp

@@ -3989,7 +3989,7 @@ static void RenderDebugOptions(const ToolChain &TC, const Driver &D,
 
   if (Args.hasFlag(options::OPT_fdebug_types_section,
                    options::OPT_fno_debug_types_section, false)) {
-    if (!T.isOSBinFormatELF()) {
+    if (!(T.isOSBinFormatELF() || T.isOSBinFormatWasm())) {
       D.Diag(diag::err_drv_unsupported_opt_for_target)
           << Args.getLastArg(options::OPT_fdebug_types_section)
                  ->getAsString(Args)

clang/test/Driver/debug-options.c

@@ -214,6 +214,9 @@
 // RUN: %clang -### -fdebug-types-section -fno-debug-types-section -target x86_64-unknown-linux %s 2>&1 \
 // RUN:        | FileCheck -check-prefix=NOFDTS %s
 //
+// RUN: %clang -### -fdebug-types-section -target wasm32-unknown-unknown %s 2>&1 \
+// RUN:        | FileCheck -check-prefix=FDTS %s
+//
 // RUN: %clang -### -fdebug-types-section -target x86_64-apple-darwin %s 2>&1 \
 // RUN:        | FileCheck -check-prefix=FDTSE %s
 //

llvm/lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -394,8 +394,9 @@ DwarfDebug::DwarfDebug(AsmPrinter *A, Module *M)
     UseSectionsAsReferences = DwarfSectionsAsReferences == Enable;
 
   // Don't generate type units for unsupported object file formats.
-  GenerateTypeUnits =
-      A->TM.getTargetTriple().isOSBinFormatELF() && GenerateDwarfTypeUnits;
+  GenerateTypeUnits = (A->TM.getTargetTriple().isOSBinFormatELF() ||
+                       A->TM.getTargetTriple().isOSBinFormatWasm()) &&
+                      GenerateDwarfTypeUnits;
 
   TheAccelTableKind = computeAccelTableKind(
       DwarfVersion, GenerateTypeUnits, DebuggerTuning, A->TM.getTargetTriple());

llvm/lib/MC/MCObjectFileInfo.cpp

@@ -963,9 +963,11 @@ MCSection *MCObjectFileInfo::getDwarfComdatSection(const char *Name,
   case Triple::ELF:
     return Ctx->getELFSection(Name, ELF::SHT_PROGBITS, ELF::SHF_GROUP, 0,
                               utostr(Hash));
+  case Triple::Wasm:
+    return Ctx->getWasmSection(Name, SectionKind::getMetadata(), utostr(Hash),
+                               MCContext::GenericSectionID);
   case Triple::MachO:
   case Triple::COFF:
-  case Triple::Wasm:
   case Triple::GOFF:
   case Triple::XCOFF:
   case Triple::UnknownObjectFormat:

llvm/lib/MC/WasmObjectWriter.cpp

@@ -1378,9 +1378,6 @@ uint64_t WasmObjectWriter::writeOneObject(MCAssembler &Asm,
       MCSymbol *Begin = Sec.getBeginSymbol();
       if (Begin) {
         WasmIndices[cast<MCSymbolWasm>(Begin)] = CustomSections.size();
-        if (SectionName != Begin->getName())
-          report_fatal_error("section name and begin symbol should match: " +
-                             Twine(SectionName));
       }
 
       // Separate out the producers and target features sections

llvm/test/DebugInfo/WebAssembly/dwarf-headers.ll

@@ -0,0 +1,116 @@
+; RUN: llc -dwarf-version=4 -generate-type-units \
+; RUN:     -filetype=obj -O0 -mtriple=wasm32-unknown-unknown < %s \
+; RUN:     | llvm-dwarfdump -v - | FileCheck %s --check-prefix=SINGLE-4
+
+; RUN: llc -split-dwarf-file=foo.dwo -split-dwarf-output=%t.dwo \
+; RUN:     -dwarf-version=4 -generate-type-units \
+; RUN:     -filetype=obj -O0 -mtriple=wasm32-unknown-unknown < %s \
+; RUN:     | llvm-dwarfdump -v - | FileCheck %s --check-prefix=O-4
+; RUN: llvm-dwarfdump -v %t.dwo | FileCheck %s --check-prefix=DWO-4
+
+; TODO: enable testing for dwarf v5
+; RUN: llc -dwarf-version=5 -generate-type-units \
+; RUN:     -filetype=obj -O0 -mtriple= < %s \
+; RUN:     | llvm-dwarfdump -v - | FileCheck %s --check-prefix=SINGLE-5
+
+; RUN: llc -split-dwarf-file=foo.dwo -split-dwarf-output=%t.dwo \
+; RUN:     -dwarf-version=5 -generate-type-units \
+; RUN:     -filetype=obj -O0 -mtriple= < %s \
+; RUN:     | llvm-dwarfdump -v - | FileCheck %s --check-prefix=O-5
+; RUN: llvm-dwarfdump -v %t.dwo | FileCheck %s --check-prefix=DWO-5
+
+; This test is derived from test/CodeGen/X86/dwarf-headers.ll
+
+; Looking for DWARF headers to be generated correctly.
+; There are 8 variants with 5 formats: v4 CU, v4 TU, v5 normal/partial CU,
+; v5 skeleton/split CU, v5 normal/split TU.  Some v5 variants differ only
+; in the unit_type code, and the skeleton/split CU differs from normal/partial
+; by having one extra field (dwo_id).
+; (v2 thru v4 CUs are all the same, and TUs were invented in v4,
+; so we don't bother checking older versions.)
+
+; Test case built from:
+;struct S {
+;  int s1;
+;};
+;
+;S s;
+
+; Verify the v4 non-split headers.
+; Note that we check the exact offset of the DIEs because that tells us
+; the length of the header.
+;
+; SINGLE-4: .debug_info contents:
+; SINGLE-4: 0x00000000: Compile Unit: {{.*}} version = 0x0004, abbr_offset
+; SINGLE-4: 0x0000000b: DW_TAG_compile_unit
+;
+; SINGLE-4: .debug_types contents:
+; SINGLE-4: 0x00000000: Type Unit: {{.*}} version = 0x0004, abbr_offset
+; SINGLE-4: 0x00000017: DW_TAG_type_unit
+
+; Verify the v4 split headers.
+;
+; O-4: .debug_info contents:
+; O-4: 0x00000000: Compile Unit: {{.*}} version = 0x0004, abbr_offset
+; O-4: 0x0000000b: DW_TAG_compile_unit
+;
+; DWO-4: .debug_info.dwo contents:
+; DWO-4: 0x00000000: Compile Unit: {{.*}} version = 0x0004, abbr_offset
+; DWO-4: 0x0000000b: DW_TAG_compile_unit
+;
+; DWO-4: .debug_types.dwo contents:
+; DWO-4: 0x00000000: Type Unit: {{.*}} version = 0x0004, abbr_offset
+; DWO-4: 0x00000017: DW_TAG_type_unit
+
+; Verify the v5 non-split headers. Type units come first.
+; All .debug_info sections are reported in one go, but the offset resets for
+; each new section.
+;
+; SINGLE-5: .debug_info contents:
+; SINGLE-5: 0x00000000: Type Unit: {{.*}} version = 0x0005, unit_type = DW_UT_type, abbr_offset
+; SINGLE-5: 0x00000018: DW_TAG_type_unit
+; SINGLE-5-NOT: contents:
+; SINGLE-5: 0x00000000: Compile Unit: {{.*}} version = 0x0005, unit_type = DW_UT_compile, abbr_offset
+; SINGLE-5: 0x0000000c: DW_TAG_compile_unit
+
+; Verify the v5 split headers.
+;
+; O-5: .debug_info contents:
+; O-5: 0x00000000: Compile Unit: {{.*}} version = 0x0005, unit_type = DW_UT_skeleton, abbr_offset
+; O-5-SAME:        DWO_id = 0xccd7e58ef8bf4aa6
+; O-5: 0x00000014: DW_TAG_skeleton_unit 
+;
+; DWO-5: .debug_info.dwo contents:
+; DWO-5: 0x00000000: Type Unit: {{.*}} version = 0x0005, unit_type = DW_UT_split_type, abbr_offset
+; DWO-5: 0x00000018: DW_TAG_type_unit
+; DWO-5: 0x00000033: Compile Unit: {{.*}} version = 0x0005, unit_type = DW_UT_split_compile, abbr_offset
+; DWO-5-SAME:        DWO_id = 0xccd7e58ef8bf4aa6
+; DWO-5: 0x00000047: DW_TAG_compile_unit
+
+
+; ModuleID = 't.cpp'
+source_filename = "t.cpp"
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown-wasm"
+
+%struct.S = type { i32 }
+
+@s = global %struct.S zeroinitializer, align 4, !dbg !0
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!10, !11}
+!llvm.ident = !{!12}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "s", scope: !2, file: !3, line: 5, type: !6, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !3, producer: "clang version 5.0.0 (trunk 295942)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !4, globals: !5)
+!3 = !DIFile(filename: "t.cpp", directory: "/home/probinson/projects/scratch")
+!4 = !{}
+!5 = !{!0}
+!6 = distinct !DICompositeType(tag: DW_TAG_structure_type, name: "S", file: !3, line: 1, size: 32, elements: !7, identifier: "_ZTS1S")
+!7 = !{!8}
+!8 = !DIDerivedType(tag: DW_TAG_member, name: "s1", scope: !6, file: !3, line: 2, baseType: !9, size: 32)
+!9 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!10 = !{i32 2, !"Dwarf Version", i32 4}
+!11 = !{i32 2, !"Debug Info Version", i32 3}
+!12 = !{!"clang version 5.0.0 (trunk 295942)"}