[WebAssembly] Move .debug_line section address of dead function outsi…

…de section range

Summary:
Currently we are pointing all debug information that refer removed function code
to the beginning of the code section (offset = 0). A debugger may want to
resolve code offset to the debug information, which will collide with offsets
of the live functions.

Moving offsets of dead functions outside code section range.

Reviewers: sbc100

Reviewed By: sbc100

Subscribers: dblaikie, ruiu, alexcrichton, dschuff, aprantl, jgravelle-google, aheejin, sunfish, JDevlieghere, llvm-commits

Differential Revision: https://reviews.llvm.org/D49446

llvm-svn: 342930

lld/test/wasm/debug-removed-fn.ll

@@ -0,0 +1,44 @@
+; RUN: llc -filetype=obj < %s -o %t.o
+; RUN: wasm-ld %t.o --no-entry --export=foo -o %t.wasm
+; RUN: llvm-dwarfdump -debug-line %t.wasm | FileCheck %s
+
+; CHECK: Address
+; CHECK: 0x0000000000000005
+; CHECK: 0x0000000000000000
+
+; ModuleID = 't.bc'
+target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
+target triple = "wasm32-unknown-unknown-wasm"
+
+; Function Attrs: noinline nounwind optnone
+define hidden i32 @foo() #0 !dbg !7 {
+entry:
+  ret i32 42, !dbg !11
+}
+
+; Function Attrs: noinline nounwind optnone
+define hidden i32 @bar() #0 !dbg !12 {
+entry:
+  ret i32 6, !dbg !13
+}
+
+attributes #0 = { noinline nounwind optnone "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="generic" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+!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 7.0.0 (trunk 337293)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "t.c", directory: "/d/y")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 7.0.0 (trunk 337293)"}
+!7 = distinct !DISubprogram(name: "foo", scope: !1, file: !1, line: 1, type: !8, isLocal: false, isDefinition: true, scopeLine: 1, isOptimized: false, unit: !0, retainedNodes: !2)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !DILocation(line: 2, column: 3, scope: !7)
+!12 = distinct !DISubprogram(name: "bar", scope: !1, file: !1, line: 5, type: !8, isLocal: false, isDefinition: true, scopeLine: 5, isOptimized: false, unit: !0, retainedNodes: !2)
+!13 = !DILocation(line: 6, column: 3, scope: !12)

lld/wasm/InputFiles.cpp

@@ -149,8 +149,9 @@ uint32_t ObjFile::calcNewValue(const WasmRelocation &Reloc) const {
     return getGlobalSymbol(Reloc.Index)->getGlobalIndex();
   case R_WEBASSEMBLY_FUNCTION_OFFSET_I32:
     if (auto *Sym = dyn_cast<DefinedFunction>(getFunctionSymbol(Reloc.Index))) {
-      return Sym->Function->OutputOffset +
-             Sym->Function->getFunctionCodeOffset() + Reloc.Addend;
+      if (Sym->isLive())
+        return Sym->Function->OutputOffset +
+               Sym->Function->getFunctionCodeOffset() + Reloc.Addend;
     }
     return 0;
   case R_WEBASSEMBLY_SECTION_OFFSET_I32: