reland: [clang] Don't append the working directory to absolute paths

[keith]

Summary

This fixes a bug that happens when using -fdebug-prefix-map to remap an
absolute path to a relative path. Since the path was absolute before
remapping, it is safe to assume that concatenating the remapped working
directory would be wrong.

This was originally submitted as https://reviews.llvm.org/D113718, but
reverted because when testing with dwarf 6 enabled, the tests were too
strict.

clang/lib/CodeGen/CGDebugInfo.cpp

if (llvm::sys::path::root_path(DirBuf) == DirBuf) {
       File = RemappedFile;
     } else {
       for (; FileIt != FileE; ++FileIt)
         llvm::sys::path::append(FileBuf, *FileIt);
       Dir = DirBuf;
       File = FileBuf;
     }
   } else {
+    if (!llvm::sys::path::is_absolute(FileName))
       Dir = CurDir;
     File = RemappedFile;
   }
   llvm::DIFile *F = DBuilder.createFile(File, Dir, CSInfo, Source);
   DIFileCache[FileName.data()].reset(F);
   return F;
 }
 
 std::string CGDebugInfo::remapDIPath(StringRef Path) const {

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

 // RUN: %clang_cc1 -debug-info-kind=standalone -fdebug-prefix-map=%p=%{fs-src-root}UNLIKELY_PATH%{fs-sep}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=%{fs-src-root}UNLIKELY_PATH=empty %s -emit-llvm -o - | FileCheck %s -check-prefix CHECK-EVIL
 // RUN: %clang_cc1 -debug-info-kind=standalone -fdebug-prefix-map=%p=%{fs-src-root}UNLIKELY_PATH%{fs-sep}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=%{fs-src-root}UNLIKELY_PATH%{fs-sep}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=%{fs-src-root}UNLIKELY_PATH%{fs-sep}empty %s -emit-llvm -o - -isysroot %p -debugger-tuning=lldb | FileCheck %s -check-prefix CHECK-SYSROOT
 // RUN: %clang -g -fdebug-prefix-map=%p=%{fs-src-root}UNLIKELY_PATH%{fs-sep}empty -S -c %s -emit-llvm -o - | FileCheck %s
 // RUN: %clang -g -ffile-prefix-map=%p=%{fs-src-root}UNLIKELY_PATH%{fs-sep}empty -S -c %s -emit-llvm -o - | FileCheck %s
 
+// RUN: %clang -g -fdebug-prefix-map=%p=./UNLIKELY_PATH/empty -S -c %s -emit-llvm -o - | FileCheck %s --check-prefix=CHECK-REL
+// RUN: %clang -g -ffile-prefix-map=%p=./UNLIKELY_PATH/empty -S -c %s -emit-llvm -o - | FileCheck %s --check-prefix=CHECK-REL
+
 #include "Inputs/stdio.h"
 
 int main(int argc, char **argv) {
   (void)argc;
   (void)argv;
   return 0;
 }
 

 // 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"
+
+// CHECK-REL: !DIFile(filename: "./UNLIKELY_PATH/empty{{/|\\\\}}{{.*}}",
+// CHECK-REL: !DIFile(filename: "./UNLIKELY_PATH/empty{{/|\\\\}}{{.*}}Inputs/stdio.h",
+// CHECK-REL-SAME:    directory: ""