[clang][Driver] Correct tool search path priority

Summary:
As seen in:
https://bugs.llvm.org/show_bug.cgi?id=45693

When clang looks for a tool it has a set of
possible names for it, in priority order.
Previously it would look for these names in
the program path. Then look for all the names
in the PATH.

This means that aarch64-none-elf-gcc on the PATH
would lose to gcc in the program path.
(which was /usr/bin in the bug's case)

This changes that logic to search each name in both
possible locations, then move to the next name.
Which is more what you would expect to happen when
using a non default triple.

(-B prefixes maybe should follow this logic too,
but are not changed in this patch)

Subscribers: kristof.beyls, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D79988

clang/lib/Driver/Driver.cpp

@@ -4717,13 +4717,11 @@ void Driver::generatePrefixedToolNames(
 }
 
 static bool ScanDirForExecutable(SmallString<128> &Dir,
-                                 ArrayRef<std::string> Names) {
-  for (const auto &Name : Names) {
-    llvm::sys::path::append(Dir, Name);
-    if (llvm::sys::fs::can_execute(Twine(Dir)))
-      return true;
-    llvm::sys::path::remove_filename(Dir);
-  }
+                                 const std::string &Name) {
+  llvm::sys::path::append(Dir, Name);
+  if (llvm::sys::fs::can_execute(Twine(Dir)))
+    return true;
+  llvm::sys::path::remove_filename(Dir);
   return false;
 }
 
@@ -4736,8 +4734,9 @@ std::string Driver::GetProgramPath(StringRef Name, const ToolChain &TC) const {
   for (const auto &PrefixDir : PrefixDirs) {
     if (llvm::sys::fs::is_directory(PrefixDir)) {
       SmallString<128> P(PrefixDir);
-      if (ScanDirForExecutable(P, TargetSpecificExecutables))
-        return std::string(P.str());
+      for (const auto &TargetSpecificExecutable : TargetSpecificExecutables)
+        if (ScanDirForExecutable(P, TargetSpecificExecutable))
+          return std::string(P.str());
     } else {
       SmallString<128> P((PrefixDir + Name).str());
       if (llvm::sys::fs::can_execute(Twine(P)))
@@ -4746,17 +4745,25 @@ std::string Driver::GetProgramPath(StringRef Name, const ToolChain &TC) const {
   }
 
   const ToolChain::path_list &List = TC.getProgramPaths();
-  for (const auto &Path : List) {
-    SmallString<128> P(Path);
-    if (ScanDirForExecutable(P, TargetSpecificExecutables))
-      return std::string(P.str());
-  }
+  for (const auto &TargetSpecificExecutable : TargetSpecificExecutables) {
+    // For each possible name of the tool look for it in
+    // program paths first, then the path.
+    // Higher priority names will be first, meaning that
+    // a higher priority name in the path will be found
+    // instead of a lower priority name in the program path.
+    // E.g. <triple>-gcc on the path will be found instead
+    // of gcc in the program path
+    for (const auto &Path : List) {
+      SmallString<128> P(Path);
+      if (ScanDirForExecutable(P, TargetSpecificExecutable))
+        return std::string(P.str());
+    }
 
-  // If all else failed, search the path.
-  for (const auto &TargetSpecificExecutable : TargetSpecificExecutables)
+    // Fall back to the path
     if (llvm::ErrorOr<std::string> P =
             llvm::sys::findProgramByName(TargetSpecificExecutable))
       return *P;
+  }
 
   return std::string(Name);
 }

clang/test/Driver/program-path-priority.c

@@ -0,0 +1,106 @@
+/// Don't create symlinks on Windows
+// UNSUPPORTED: system-windows
+
+/// Check the priority used when searching for tools
+/// Names and locations are usually in this order:
+/// <triple>-tool, tool, <default triple>-tool
+/// program path, PATH
+/// (from highest to lowest priority)
+/// A higher priority name found in a lower priority
+/// location will win over a lower priority name in a
+/// higher priority location.
+/// Prefix dirs (added with -B) override the location,
+/// so only name priority is accounted for, unless we fail to find
+/// anything at all in the prefix.
+
+/// Copy clang to a new dir which will be its
+/// "program path" for these tests
+// RUN: rm -rf %t && mkdir -p %t
+// RUN: ln -s %clang %t/clang
+
+/// No gccs at all, nothing is found
+// RUN: env "PATH=" %t/clang -### -target notreal-none-elf %s 2>&1 | \
+// RUN:   FileCheck --check-prefix=NO_NOTREAL_GCC %s
+// NO_NOTREAL_GCC-NOT: notreal-none-elf-gcc
+// NO_NOTREAL_GCC-NOT: /gcc
+
+/// <triple>-gcc in program path is found
+// RUN: touch %t/notreal-none-elf-gcc && chmod +x %t/notreal-none-elf-gcc
+// RUN: env "PATH=" %t/clang -### -target notreal-none-elf %s 2>&1 | \
+// RUN:   FileCheck --check-prefix=PROG_PATH_NOTREAL_GCC %s
+// PROG_PATH_NOTREAL_GCC: notreal-none-elf-gcc
+
+/// <triple>-gcc on the PATH is found
+// RUN: mkdir -p %t/env
+// RUN: rm %t/notreal-none-elf-gcc
+// RUN: touch %t/env/notreal-none-elf-gcc && chmod +x %t/env/notreal-none-elf-gcc
+// RUN: env "PATH=%t/env/" %t/clang -### -target notreal-none-elf %s 2>&1 | \
+// RUN:   FileCheck --check-prefix=ENV_PATH_NOTREAL_GCC %s
+// ENV_PATH_NOTREAL_GCC: env/notreal-none-elf-gcc
+
+/// <triple>-gcc in program path is preferred to one on the PATH
+// RUN: touch %t/notreal-none-elf-gcc && chmod +x %t/notreal-none-elf-gcc
+// RUN: env "PATH=%t/env/" %t/clang -### -target notreal-none-elf %s 2>&1 | \
+// RUN:   FileCheck --check-prefix=BOTH_NOTREAL_GCC %s
+// BOTH_NOTREAL_GCC: notreal-none-elf-gcc
+// BOTH_NOTREAL_GCC-NOT: env/notreal-none-elf-gcc
+
+/// On program path, <triple>-gcc is preferred to plain gcc
+// RUN: touch %t/gcc && chmod +x %t/gcc
+// RUN: env "PATH=" %t/clang -### -target notreal-none-elf %s 2>&1 | \
+// RUN:   FileCheck --check-prefix=NOTREAL_GCC_PREFERRED %s
+// NOTREAL_GCC_PREFERRED: notreal-none-elf-gcc
+// NOTREAL_GCC_PREFERRED-NOT: /gcc
+
+/// <triple>-gcc on the PATH is preferred to gcc in program path
+// RUN: rm %t/notreal-none-elf-gcc
+// RUN: env "PATH=%t/env/" %t/clang -### -target notreal-none-elf %s 2>&1 | \
+// RUN:   FileCheck --check-prefix=NOTREAL_PATH_OVER_GCC_PROG %s
+// NOTREAL_PATH_OVER_GCC_PROG: env/notreal-none-elf-gcc
+// NOTREAL_PATH_OVER_GCC_PROG-NOT: /gcc
+
+/// <triple>-gcc on the PATH is preferred to gcc on the PATH
+// RUN: rm %t/gcc
+// RUN: touch %t/env/gcc && chmod +x %t/env/gcc
+// RUN: env "PATH=%t/env/" %t/clang -### -target notreal-none-elf %s 2>&1 | \
+// RUN:   FileCheck --check-prefix=NOTREAL_PATH_OVER_GCC_PATH %s
+// NOTREAL_PATH_OVER_GCC_PATH: env/notreal-none-elf-gcc
+// NOTREAL_PATH_OVER_GCC_PATH-NOT: /gcc
+
+/// <default-triple>-gcc has lowest priority so <triple>-gcc
+/// on PATH beats default triple in program path
+// RUN: touch %t/%target_triple-gcc && chmod +x %t/%target_triple-gcc
+// RUN: env "PATH=%t/env/" %t/clang -### -target notreal-none-elf %s 2>&1 | \
+// RUN:   FileCheck --check-prefix=DEFAULT_TRIPLE_GCC %s
+// DEFAULT_TRIPLE_GCC: env/notreal-none-elf-gcc
+
+/// plain gcc on PATH beats default triple in program path
+// RUN: rm %t/env/notreal-none-elf-gcc
+// RUN: env "PATH=%t/env/" %t/clang -### -target notreal-none-elf %s 2>&1 | \
+// RUN:   FileCheck --check-prefix=DEFAULT_TRIPLE_NO_NOTREAL %s
+// DEFAULT_TRIPLE_NO_NOTREAL: env/gcc
+// DEFAULT_TRIPLE_NO_NOTREAL-NOT: -gcc
+
+/// default triple only chosen when no others are present
+// RUN: rm %t/env/gcc
+// RUN: env "PATH=%t/env/" %t/clang -### -target notreal-none-elf %s 2>&1 | \
+// RUN:   FileCheck --check-prefix=DEFAULT_TRIPLE_NO_OTHERS %s
+// DEFAULT_TRIPLE_NO_OTHERS: -gcc
+// DEFAULT_TRIPLE_NO_OTHERS-NOT: notreal-none-elf-gcc
+// DEFAULT_TRIPLE_NO_OTHERS-NOT: /gcc
+
+/// -B paths are searched separately so default triple will win
+/// if put in one of those even if other paths have higher priority names
+// RUN: mkdir -p %t/prefix
+// RUN: mv %t/%target_triple-gcc %t/prefix
+// RUN: touch %t/notreal-none-elf-gcc && chmod +x %t/notreal-none-elf-gcc
+// RUN: env "PATH=" %t/clang -### -target notreal-none-elf %s -B %t/prefix 2>&1 | \
+// RUN:   FileCheck --check-prefix=DEFAULT_TRIPLE_IN_PREFIX %s
+// DEFAULT_TRIPLE_IN_PREFIX: prefix/{{.*}}-gcc
+// DEFAULT_TRIPLE_IN_PREFIX-NOT: notreal-none-elf-gcc
+
+/// Only if there is nothing in the prefix will we search other paths
+// RUN: rm %t/prefix/%target_triple-gcc
+// RUN: env "PATH=" %t/clang -### -target notreal-none-elf %s -B %t/prefix 2>&1 | \
+// RUN:   FileCheck --check-prefix=EMPTY_PREFIX_DIR %s
+// EMPTY_PREFIX_DIR: notreal-none-elf-gcc

clang/test/lit.cfg.py

@@ -46,6 +46,8 @@
 config.substitutions.append(
     ('%src_include_dir', config.clang_src_dir + '/include'))
 
+config.substitutions.append(
+    ('%target_triple', config.target_triple))
 
 # Propagate path to symbolizer for ASan/MSan.
 llvm_config.with_system_environment(