7 files changed, 15 insertions, 17 deletions
diff --git a/clang/include/clang/Basic/CodeGenOptions.h b/clang/include/clang/Basic/CodeGenOptions.h
index 6192d3f..662271f 100644
--- a/clang/include/clang/Basic/CodeGenOptions.h
+++ b/clang/include/clang/Basic/CodeGenOptions.h
@@ -206,7 +206,7 @@ public:
   /// if non-empty.
   std::string RecordCommandLine;
 
-  std::map<std::string, std::string> DebugPrefixMap;
+  llvm::SmallVector<std::pair<std::string, std::string>, 0> DebugPrefixMap;
   std::map<std::string, std::string> CoveragePrefixMap;
 
   /// The ABI to use for passing floating point arguments.
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index eb48c14..c8f505a 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -3218,7 +3218,8 @@ def fdebug_default_version: Joined<["-"], "fdebug-default-version=">, Group<f_Gr
 def fdebug_prefix_map_EQ
   : Joined<["-"], "fdebug-prefix-map=">, Group<f_Group>,
     Flags<[CC1Option,CC1AsOption]>,
-    HelpText<"remap file source paths in debug info">;
+    MetaVarName<"<old>=<new>">,
+    HelpText<"For paths in debug info, remap directory <old> to <new>. If multiple options match a path, the last option wins">;
 def fcoverage_prefix_map_EQ
   : Joined<["-"], "fcoverage-prefix-map=">, Group<f_Group>,
     Flags<[CC1Option]>,
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index 5100d6c..2cf7b02 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -73,8 +73,6 @@ CGDebugInfo::CGDebugInfo(CodeGenModule &CGM)
     : CGM(CGM), DebugKind(CGM.getCodeGenOpts().getDebugInfo()),
       DebugTypeExtRefs(CGM.getCodeGenOpts().DebugTypeExtRefs),
       DBuilder(CGM.getModule()) {
-  for (const auto &KV : CGM.getCodeGenOpts().DebugPrefixMap)
-    DebugPrefixMap[KV.first] = KV.second;
   CreateCompileUnit();
 }
 
@@ -470,12 +468,9 @@ llvm::DIFile *CGDebugInfo::createFile(
 }
 
 std::string CGDebugInfo::remapDIPath(StringRef Path) const {
-  if (DebugPrefixMap.empty())
-    return Path.str();
-
   SmallString<256> P = Path;
-  for (const auto &Entry : DebugPrefixMap)
-    if (llvm::sys::path::replace_path_prefix(P, Entry.first, Entry.second))
+  for (auto &[From, To] : llvm::reverse(CGM.getCodeGenOpts().DebugPrefixMap))
+    if (llvm::sys::path::replace_path_prefix(P, From, To))
       break;
   return P.str().str();
 }
diff --git a/clang/lib/CodeGen/CGDebugInfo.h b/clang/lib/CodeGen/CGDebugInfo.h
index 5a3839d..5c42d36 100644
--- a/clang/lib/CodeGen/CGDebugInfo.h
+++ b/clang/lib/CodeGen/CGDebugInfo.h
@@ -86,9 +86,6 @@ class CGDebugInfo {
   /// Cache of previously constructed Types.
   llvm::DenseMap<const void *, llvm::TrackingMDRef> TypeCache;
 
-  std::map<llvm::StringRef, llvm::StringRef, std::greater<llvm::StringRef>>
-      DebugPrefixMap;
-
   /// Cache that maps VLA types to size expressions for that type,
   /// represented by instantiated Metadata nodes.
   llvm::SmallDenseMap<QualType, llvm::Metadata *> SizeExprCache;
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 71204de..a148136 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1696,8 +1696,7 @@ bool CompilerInvocation::ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args,
 
   for (const auto &Arg : Args.getAllArgValues(OPT_fdebug_prefix_map_EQ)) {
     auto Split = StringRef(Arg).split('=');
-    Opts.DebugPrefixMap.insert(
-        {std::string(Split.first), std::string(Split.second)});
+    Opts.DebugPrefixMap.emplace_back(Split.first, Split.second);
   }
 
   for (const auto &Arg : Args.getAllArgValues(OPT_fcoverage_prefix_map_EQ)) {
diff --git a/clang/test/CodeGen/debug-prefix-map.c b/clang/test/CodeGen/debug-prefix-map.c
index f604f16..e242180 100644
--- a/clang/test/CodeGen/debug-prefix-map.c
+++ b/clang/test/CodeGen/debug-prefix-map.c
@@ -9,6 +9,10 @@
 // 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
 
+// RUN: rm -rf %t && mkdir -p %t/a/b && cp %s %t/a/b/c.c
+// RUN: %clang_cc1 -emit-llvm -debug-info-kind=standalone -I%S -fdebug-prefix-map=%t/a/b=y -fdebug-prefix-map=%t/a=x %t/a/b/c.c -o - | FileCheck %s --check-prefix=CHECK-X
+// RUN: %clang_cc1 -emit-llvm -debug-info-kind=standalone -I%S -fdebug-prefix-map=%t/a=x -fdebug-prefix-map=%t/a/b=y %t/a/b/c.c -o - | FileCheck %s --check-prefix=CHECK-Y
+
 #include "Inputs/stdio.h"
 
 int main(int argc, char **argv) {
@@ -47,3 +51,6 @@ void test_rewrite_includes(void) {
 // CHECK-REL: !DIFile(filename: "./UNLIKELY_PATH/empty{{/|\\\\}}{{.*}}",
 // CHECK-REL: !DIFile(filename: "./UNLIKELY_PATH/empty{{/|\\\\}}{{.*}}Inputs/stdio.h",
 // CHECK-REL-SAME:    directory: ""
+
+// CHECK-X: !DIFile(filename: "x{{/|\\\\}}b{{/|\\\\}}c.c", directory: "")
+// CHECK-Y: !DIFile(filename: "y{{/|\\\\}}c.c", directory: "")
diff --git a/clang/tools/driver/cc1as_main.cpp b/clang/tools/driver/cc1as_main.cpp
index ee54a0f7..ecfb1be 100644
--- a/clang/tools/driver/cc1as_main.cpp
+++ b/clang/tools/driver/cc1as_main.cpp
@@ -97,7 +97,7 @@ struct AssemblerInvocation {
   std::string DwarfDebugFlags;
   std::string DwarfDebugProducer;
   std::string DebugCompilationDir;
-  std::map<const std::string, const std::string> DebugPrefixMap;
+  llvm::SmallVector<std::pair<std::string, std::string>, 0> DebugPrefixMap;
   llvm::DebugCompressionType CompressDebugSections =
       llvm::DebugCompressionType::None;
   std::string MainFileName;
@@ -275,8 +275,7 @@ bool AssemblerInvocation::CreateFromArgs(AssemblerInvocation &Opts,
 
   for (const auto &Arg : Args.getAllArgValues(OPT_fdebug_prefix_map_EQ)) {
     auto Split = StringRef(Arg).split('=');
-    Opts.DebugPrefixMap.insert(
-        {std::string(Split.first), std::string(Split.second)});
+    Opts.DebugPrefixMap.emplace_back(Split.first, Split.second);
   }
 
   // Frontend Options