swiftlang · benlangmuir · May 22, 2025 · May 21, 2025 · May 21, 2025 · May 21, 2025
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
@@ -8836,11 +8836,15 @@ def fdepscan_include_tree : Flag<["-"], "fdepscan-include-tree">,
 //
 // FIXME: Add DepscanOption flag.
 def fdepscan_prefix_map_EQ : Joined<["-"], "fdepscan-prefix-map=">,
-    Group<f_Group>, Visibility<[ClangOption, CC1Option]>,
+    Group<f_Group>, Visibility<[ClangOption]>,
     MetaVarName<"<old>=<new>">,
     HelpText<"With -fdepscan, seamlessly filter the CAS filesystem to"
-             " apply the given prefix, updating the command-line to match.">,
-    MarshallingInfoStringVector<FrontendOpts<"PathPrefixMappings">>;
+             " apply the given prefix, updating the command-line to match.">;
+def fdepscan_prefix_map : MultiArg<["-"], "fdepscan-prefix-map", 2>,
+    Group<f_Group>, Visibility<[ClangOption, CC1Option]>,
+    MetaVarName<"<old> <new>">,
+    HelpText<"With -fdepscan, seamlessly filter the CAS filesystem to"
+             " apply the given prefix, updating the command-line to match.">;
 def fdepscan_prefix_map_sdk_EQ :
     Joined<["-"], "fdepscan-prefix-map-sdk=">,
     Group<f_Group>, MetaVarName<"<new>">,

diff --git a/clang/include/clang/Frontend/CompileJobCacheKey.h b/clang/include/clang/Frontend/CompileJobCacheKey.h
@@ -48,7 +48,7 @@ struct CompileJobCachingOptions {
   /// See \c FrontendOptions::WriteOutputAsCASID.
   bool WriteOutputAsCASID;
   /// See \c FrontendOptions::PathPrefixMappings.
-  std::vector<std::string> PathPrefixMappings;
+  std::vector<std::pair<std::string, std::string>> PathPrefixMappings;
 };
 
 /// Create a cache key for the given \c CompilerInvocation as a \c CASID. If \p

diff --git a/clang/include/clang/Frontend/FrontendOptions.h b/clang/include/clang/Frontend/FrontendOptions.h
@@ -528,7 +528,7 @@ class FrontendOptions {
   /// When caching is enabled, represents remappings for all the file paths that
   /// the compilation may access. This is useful for canonicalizing the
   /// compilation for caching purposes.
-  std::vector<std::string> PathPrefixMappings;
+  std::vector<std::pair<std::string, std::string>> PathPrefixMappings;
 
   // Currently this is only used as part of the `-extract-api` action.
   // A comma separated list of files providing a list of APIs to

diff --git a/clang/include/clang/Tooling/DependencyScanning/ScanAndUpdateArgs.h b/clang/include/clang/Tooling/DependencyScanning/ScanAndUpdateArgs.h
@@ -48,7 +48,7 @@ struct DepscanPrefixMapping {
                                     llvm::PrefixMapper &Mapper);
 
   /// Add path mappings to the \p Mapper.
-  static void configurePrefixMapper(ArrayRef<std::string> PathPrefixMappings,
+  static void configurePrefixMapper(ArrayRef<std::pair<std::string, std::string>> PathPrefixMappings,
                                     llvm::PrefixMapper &Mapper);
 
   /// Apply the mappings from \p Mapper to \p Invocation.

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -5059,8 +5059,9 @@ void Clang::AddPrefixMappingOptions(const ArgList &Args, ArgStringList &CmdArgs,
 
   if (Arg *A = Args.getLastArg(options::OPT_fdepscan_prefix_map_sdk_EQ)) {
     if (IsPathApplicableAsPrefix(Sysroot)) {
-      CmdArgs.push_back(Args.MakeArgString(Twine("-fdepscan-prefix-map=") +
-                                           *Sysroot + "=" + A->getValue()));
+      CmdArgs.push_back("-fdepscan-prefix-map");
+      CmdArgs.push_back(Args.MakeArgString(*Sysroot));
+      CmdArgs.push_back(Args.MakeArgString(A->getValue()));
     } else {
       // FIXME: warning if we cannot infer sdk
     }
@@ -5075,22 +5076,31 @@ void Clang::AddPrefixMappingOptions(const ArgList &Args, ArgStringList &CmdArgs,
       Guess = llvm::sys::path::parent_path(Guess);
     }
     if (IsPathApplicableAsPrefix(Guess)) {
-      CmdArgs.push_back(Args.MakeArgString(Twine("-fdepscan-prefix-map=") +
-                                           Guess + "=" + A->getValue()));
+      CmdArgs.push_back("-fdepscan-prefix-map");
+      CmdArgs.push_back(Args.MakeArgString(Guess));
+      CmdArgs.push_back(Args.MakeArgString(A->getValue()));
     } else {
       // FIXME: warning if we cannot infer toolchain
     }
   }
 
-  for (const Arg *A : Args.filtered(options::OPT_fdepscan_prefix_map_EQ)) {
+  for (const Arg *A : Args.filtered(options::OPT_fdepscan_prefix_map, options::OPT_fdepscan_prefix_map_EQ)) {
     A->claim();
-    StringRef Map = A->getValue();
-    StringRef Prefix = Map.split('=').first;
-    if (Prefix.size() == Map.size() || !IsPathApplicableAsPrefix(Prefix)) {
+    StringRef Prefix, MapTarget;
+    if (A->getOption().matches(options::OPT_fdepscan_prefix_map_EQ)) {
+      StringRef Map = A->getValue();
+      std::tie(Prefix, MapTarget) = Map.split('=');
+    } else {
+      Prefix = A->getValue(0);
+      MapTarget = A->getValue(1);
+    }
+    if (MapTarget.size() == 0 || !IsPathApplicableAsPrefix(Prefix)) {
       D.Diag(diag::err_drv_invalid_argument_to_option)
           << A->getValue() << A->getOption().getName();
     } else {
-      A->render(Args, CmdArgs);
+      CmdArgs.push_back("-fdepscan-prefix-map");
+      CmdArgs.push_back(Args.MakeArgString(Prefix));
+      CmdArgs.push_back(Args.MakeArgString(MapTarget));
     }
   }
 }

diff --git a/clang/lib/Frontend/CompileJobCache.cpp b/clang/lib/Frontend/CompileJobCache.cpp
@@ -330,8 +330,7 @@ std::optional<int> CompileJobCache::initialize(CompilerInstance &Clang) {
 
   llvm::PrefixMapper PrefixMapper;
   llvm::SmallVector<llvm::MappedPrefix> Split;
-  llvm::MappedPrefix::transformJoinedIfValid(CacheOpts.PathPrefixMappings,
-                                             Split);
+  llvm::MappedPrefix::transformPairs(CacheOpts.PathPrefixMappings, Split);
   for (const auto &MappedPrefix : Split) {
     // We use the inverse mapping because the \p PrefixMapper will be used for
     // de-canonicalization of paths.
@@ -629,7 +628,7 @@ Expected<std::optional<int>> CompileJobCache::replayCachedResult(
 
   llvm::PrefixMapper PrefixMapper;
   llvm::SmallVector<llvm::MappedPrefix> Split;
-  llvm::MappedPrefix::transformJoinedIfValid(
+  llvm::MappedPrefix::transformPairs(
       Clang.getFrontendOpts().PathPrefixMappings, Split);
   for (const auto &MappedPrefix : Split) {
     // We use the inverse mapping because the \p PrefixMapper will be used for

diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -86,6 +86,7 @@
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
+#include "llvm/Support/PrefixMapper.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/Regex.h"
 #include "llvm/Support/VersionTuple.h"
@@ -3155,6 +3156,9 @@ static void GenerateFrontendArgs(const FrontendOptions &Opts,
   for (const auto &A : Opts.ModuleCacheKeys)
     GenerateMultiArg(Consumer, OPT_fmodule_file_cache_key, {A.first, A.second});
 
+  for (const auto &A : Opts.PathPrefixMappings)
+    GenerateMultiArg(Consumer, OPT_fdepscan_prefix_map, {A.first, A.second});
+
   if (Opts.AuxTargetCPU)
     GenerateArg(Consumer, OPT_aux_target_cpu, *Opts.AuxTargetCPU);
 
@@ -3381,6 +3385,13 @@ static bool ParseFrontendArgs(FrontendOptions &Opts, ArgList &Args,
     Opts.ModuleCacheKeys.emplace_back(Values[0], Values[1]);
   }
 
+  // Handle path prefix mappings
+  for (const Arg *A : Args.filtered(OPT_fdepscan_prefix_map)) {
+    ArrayRef<const char *> Values = A->getValues();
+    assert(Values.size() == 2);
+    Opts.PathPrefixMappings.emplace_back(Values[0], Values[1]);
+  }
+
   if (Opts.ProgramAction != frontend::GenerateModule && Opts.IsSystemModule)
     Diags.Report(diag::err_drv_argument_only_allowed_with) << "-fsystem-module"
                                                            << "-emit-module";

diff --git a/clang/lib/Tooling/DependencyScanning/ScanAndUpdateArgs.cpp b/clang/lib/Tooling/DependencyScanning/ScanAndUpdateArgs.cpp
@@ -143,7 +143,7 @@ void DepscanPrefixMapping::remapInvocationPaths(CompilerInvocation &Invocation,
   // Pass the remappings so that we can map cached diagnostics to the local
   // paths during diagnostic rendering.
   for (const llvm::MappedPrefix &Map : Mapper.getMappings()) {
-    FrontendOpts.PathPrefixMappings.push_back(Map.Old + "=" + Map.New);
+    FrontendOpts.PathPrefixMappings.emplace_back(Map.Old, Map.New);
   }
 
   auto mapInPlaceAll = [&](std::vector<std::string> &Vector) {
@@ -244,12 +244,12 @@ void DepscanPrefixMapping::configurePrefixMapper(const CompilerInvocation &CI,
 }
 
 void DepscanPrefixMapping::configurePrefixMapper(
-    ArrayRef<std::string> PathPrefixMappings, llvm::PrefixMapper &Mapper) {
+    ArrayRef<std::pair<std::string, std::string>> PathPrefixMappings, llvm::PrefixMapper &Mapper) {
   if (PathPrefixMappings.empty())
     return;
 
   llvm::SmallVector<llvm::MappedPrefix> Split;
-  llvm::MappedPrefix::transformJoinedIfValid(PathPrefixMappings, Split);
+  llvm::MappedPrefix::transformPairs(PathPrefixMappings, Split);
   for (auto &MappedPrefix : Split)
     Mapper.add(MappedPrefix);
 

diff --git a/llvm/include/llvm/Support/PrefixMapper.h b/llvm/include/llvm/Support/PrefixMapper.h
@@ -11,6 +11,7 @@
 
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/IntrusiveRefCntPtr.h"
+#include "llvm/ADT/SmallVector.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/Path.h"
 #include <optional>
@@ -48,6 +49,8 @@ struct MappedPrefix {
                                      SmallVectorImpl<MappedPrefix> &Split);
   static void transformJoinedIfValid(ArrayRef<std::string> Joined,
                                      SmallVectorImpl<MappedPrefix> &Split);
+  static void transformPairs(ArrayRef<std::pair<std::string, std::string>> Pairs,
+                             SmallVectorImpl<MappedPrefix> & Split);
 };
 
 /// Remap path prefixes.

diff --git a/llvm/lib/Support/PrefixMapper.cpp b/llvm/lib/Support/PrefixMapper.cpp
@@ -70,6 +70,13 @@ void MappedPrefix::transformJoinedIfValid(
   transformJoinedImpl</*StopOnInvalid*/ false>(Joined, Split);
 }
 
+void MappedPrefix::transformPairs(
+    ArrayRef<std::pair<std::string, std::string>> Pairs, SmallVectorImpl<MappedPrefix> &Split) {
+  for (auto &Pair : Pairs) {
+    Split.push_back(MappedPrefix{Pair.first, Pair.second});
+  }
+}
+
 /// FIXME: Copy/pasted from llvm/lib/Support/Path.cpp.
 static bool startsWith(StringRef Path, StringRef Prefix,
                        sys::path::Style PathStyle) {

diff --git a/llvm/unittests/Support/PrefixMapperTest.cpp b/llvm/unittests/Support/PrefixMapperTest.cpp
@@ -125,6 +125,21 @@ TEST(MappedPrefixTest, transformJoinedIfValid) {
   EXPECT_EQ(ArrayRef(ExpectedSplit), ArrayRef(ComputedSplit));
 }
 
+TEST(PrefixMapperTest, transformPairs) {
+  SmallVector<std::pair<std::string, std::string>> PrefixMappings = {
+    {"", ""}, {"a", "b"}, {"", "a"}, {"a", ""}, {"=a=b=", "=c=d==="}
+  };
+  MappedPrefix ExpectedSplit[] = {
+    MappedPrefix{"", ""}, MappedPrefix{"a", "b"},
+    MappedPrefix{"", "a"}, MappedPrefix{"a", ""},
+    MappedPrefix{"=a=b=", "=c=d==="},
+  };
+
+  SmallVector<MappedPrefix> ComputedSplit;
+  MappedPrefix::transformPairs(PrefixMappings, ComputedSplit);
+  EXPECT_EQ(ArrayRef(ExpectedSplit), ArrayRef(ComputedSplit));
+}
+
 TEST(PrefixMapperTest, construct) {
   for (auto PathStyle : {
            sys::path::Style::posix,