[Driver] Give devtoolset path precedence over InstalledDir

[nikic]

Summary

This is a followup to the change from c5fe10f365247c3dd9416b7ec8bad73a60b5946e. While that commit correctly adds the bindir from devtoolset to the path, the driver dir / install dir still comes first. This means we'll still end up picking /usr/bin/ld rather than the one from devtoolset.

Unfortunately, I don't see any way to test this. In the environment the tests are run, this would only result in a behavior difference if there is an ld binary present in the LLVM build directory, which isn't the case.

[MaskRay]

Unfortunately, I don't see any way to test this. In the environment the tests are run, this would only result in a behavior difference if there is an ld binary present in the LLVM build directory, which isn't the case.

You can use clang/unittests/Driver/DistroTest.cpp

[nikic]

In D151203#4365102, @MaskRay wrote:

Unfortunately, I don't see any way to test this. In the environment the tests are run, this would only result in a behavior difference if there is an ld binary present in the LLVM build directory, which isn't the case.

You can use clang/unittests/Driver/DistroTest.cpp

Thanks for the pointer! I gave it a try and it does work, but requires switching some code to VFS first. I've put up https://reviews.llvm.org/D151327 to do that independently of this patch.

[nikic]

In D151203#4368148, @nikic wrote:

In D151203#4365102, @MaskRay wrote:

Unfortunately, I don't see any way to test this. In the environment the tests are run, this would only result in a behavior difference if there is an ld binary present in the LLVM build directory, which isn't the case.

You can use clang/unittests/Driver/DistroTest.cpp

Thanks for the pointer! I gave it a try and it does work, but requires switching some code to VFS first. I've put up https://reviews.llvm.org/D151327 to do that independently of this patch.

Unfortunately this didn't work out, because the code relies on platform-specific behavior that's not straightforward to migrate to VFS.

clang/lib/Driver/ToolChains/Linux.cpp

if ((Triple.isARM() || Triple.isAArch64()) && Triple.isAndroid()) {
     ExtraOpts.push_back("-z");
     ExtraOpts.push_back("max-page-size=4096");
   }
 
   if (GCCInstallation.getParentLibPath().contains("opt/rh/"))
     // With devtoolset on RHEL, we want to add a bin directory that is relative
     // to the detected gcc install, because if we are using devtoolset gcc then
     // we want to use other tools from devtoolset (e.g. ld) instead of the
-    // standard system tools.
-    PPaths.push_back(Twine(GCCInstallation.getParentLibPath() +
-                     "/../bin").str());
+    // standard system tools. This should take precedence over InstalledDir.
+    PPaths.insert(PPaths.begin(),
+                  Twine(GCCInstallation.getParentLibPath() + "/../bin").str());
 
   if (Arch == llvm::Triple::arm || Arch == llvm::Triple::thumb)
     ExtraOpts.push_back("-X");
 
   const bool IsAndroid = Triple.isAndroid();
   const bool IsMips = Triple.isMIPS();
   const bool IsHexagon = Arch == llvm::Triple::hexagon;
   const bool IsRISCV = Triple.isRISCV();