Allow remapping the sysroot with -fdebug-prefix-map.

[aprantl]

Summary

rdar://problem/55685132

[aprantl]

Don't try to be too clever with the strings.

[PaulkaToast]

This seems to be causing a failure in our buildbot, mind taking a look? (:

[aprantl]

Yeah, screwed up during rebasing and accidentally committed an extra file from a different review I reverted and relanded the patch now and the bots are running again. Sorry for the noise.

clang/lib/CodeGen/CGDebugInfo.cpp

TheCU = DBuilder.createCompileUnit(
       LangTag, CUFile, CGOpts.EmitVersionIdentMetadata ? Producer : "",
       LO.Optimize || CGOpts.PrepareForLTO || CGOpts.PrepareForThinLTO,
       CGOpts.DwarfDebugFlags, RuntimeVers, CGOpts.SplitDwarfFile, EmissionKind,
       DwoId, CGOpts.SplitDwarfInlining, CGOpts.DebugInfoForProfiling,
       CGM.getTarget().getTriple().isNVPTX()
           ? llvm::DICompileUnit::DebugNameTableKind::None
           : static_cast<llvm::DICompileUnit::DebugNameTableKind>(
                 CGOpts.DebugNameTable),
-      CGOpts.DebugRangesBaseAddress, Sysroot, SDK);
+      CGOpts.DebugRangesBaseAddress, remapDIPath(Sysroot), SDK);
 }
 
 llvm::DIType *CGDebugInfo::CreateType(const BuiltinType *BT) {
   llvm::dwarf::TypeKind Encoding;
   StringRef BTName;
   switch (BT->getKind()) {
 #define BUILTIN_TYPE(Id, SingletonId)
 #define PLACEHOLDER_TYPE(Id, SingletonId) case BuiltinType::Id:

clang/test/CodeGen/debug-prefix-map.c

 // RUN: %clang_cc1 -debug-info-kind=standalone -fdebug-prefix-map=%p=/UNLIKELY_PATH/empty %s -emit-llvm -o - | FileCheck %s -check-prefix CHECK-NO-MAIN-FILE-NAME
 // RUN: %clang_cc1 -debug-info-kind=standalone -fdebug-prefix-map=%p=/UNLIKELY_PATH=empty %s -emit-llvm -o - | FileCheck %s -check-prefix CHECK-EVIL
 // RUN: %clang_cc1 -debug-info-kind=standalone -fdebug-prefix-map=%p=/UNLIKELY_PATH/empty %s -emit-llvm -o - -main-file-name debug-prefix-map.c | FileCheck %s
 // RUN: %clang_cc1 -debug-info-kind=standalone -fdebug-prefix-map=%p=/UNLIKELY_PATH/empty %s -emit-llvm -o - -fdebug-compilation-dir %p | FileCheck %s -check-prefix CHECK-COMPILATION-DIR
+// RUN: %clang_cc1 -debug-info-kind=standalone -fdebug-prefix-map=%p=/UNLIKELY_PATH/empty %s -emit-llvm -o - -isysroot %p -debugger-tuning=lldb | FileCheck %s -check-prefix CHECK-SYSROOT
 // RUN: %clang -g -fdebug-prefix-map=%p=/UNLIKELY_PATH/empty -S -c %s -emit-llvm -o - | FileCheck %s
 // RUN: %clang -g -ffile-prefix-map=%p=/UNLIKELY_PATH/empty -S -c %s -emit-llvm -o - | FileCheck %s
 
 #include "Inputs/stdio.h"
 
 int main(int argc, char **argv) {
   (void)argc;
   (void)argv;

 // CHECK: !DIFile(filename: "/UNLIKELY_PATH/empty{{/|\\\\}}{{.*}}"
 // CHECK: !DIFile(filename: "/UNLIKELY_PATH/empty{{/|\\\\}}{{.*}}Inputs/stdio.h",
 // CHECK-SAME:    directory: "{{()|(.*:.*)}}")
 // CHECK-NOT: !DIFile(filename:
 
 // CHECK-COMPILATION-DIR: !DIFile(filename: "{{.*}}", directory: "/UNLIKELY_PATH/empty")
 // CHECK-COMPILATION-DIR: !DIFile(filename: "{{.*}}Inputs/stdio.h", directory: "/UNLIKELY_PATH/empty")
 // CHECK-COMPILATION-DIR-NOT: !DIFile(filename:
+// CHECK-SYSROOT: !DICompileUnit({{.*}}sysroot: "/UNLIKELY_PATH/empty"

llvm/lib/DWARFLinker/DWARFLinker.cpp

 static uint64_t getDwoId(const DWARFDie &CUDie, const DWARFUnit &Unit) {
   auto DwoId = dwarf::toUnsigned(
       CUDie.find({dwarf::DW_AT_dwo_id, dwarf::DW_AT_GNU_dwo_id}));
   if (DwoId)
     return *DwoId;
   return 0;
 }
 
+static std::string remapPath(std::string Path,
+                             const objectPrefixMap &ObjectPrefixMap) {
+  StringRef PathRef(Path);
+  for (const auto &Entry : ObjectPrefixMap)
+    if (PathRef.startswith(Entry.first))
+      return (Twine(Entry.second) + PathRef.substr(Entry.first.size())).str();
+  return Path;
+}
+
 bool DWARFLinker::registerModuleReference(
     DWARFDie CUDie, const DWARFUnit &Unit, const DwarfFile &File,
     OffsetsStringPool &StringPool, UniquingStringPool &UniquingStringPool,
     DeclContextTree &ODRContexts, uint64_t ModulesEndOffset, unsigned &UnitID,
     bool IsLittleEndian, unsigned Indent, bool Quiet) {
   std::string PCMfile = dwarf::toString(
       CUDie.find({dwarf::DW_AT_dwo_name, dwarf::DW_AT_GNU_dwo_name}), "");
   if (PCMfile.empty())