[LLVMbugs] [Bug 12479] New: GCCInstallationDetector: add an option to force a specific version of gcc

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=12479

             Bug #: 12479
           Summary: GCCInstallationDetector: add an option to force a
                    specific version of gcc
           Product: clang
           Version: trunk
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Driver
        AssignedTo: unassignedclangbugs at nondot.org
        ReportedBy: voyageursp at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


Gentoo bugreport is here: https://bugs.gentoo.org/show_bug.cgi?id=406163

The new gcc detector currently in trunk works fine with our setups, though it
is designed to always pick up the highest installed gcc version

But we can have multiple gcc installed at the same time (especially for people
testing compilers), for example a stable 4.5.3, 4.6.2 which should be unmasked
soon, 4.7.0 in testing, and even live versions. And in this case the gcc
version to use is usually not the highest

In clang < 3.0, the ebuild played with the --with-cxx-* variables to work
around this (hardcoding to the currently active compiler)

This could be solved by a new "-gcc-version" option, close to the existing
"-gcc-prefix" one (tough setting this at configure step may not be as useful).

When getting to Generic_GCC::GCCInstallationDetector::ScanLibDirForGCCTriple,
before starting looping on directories found in LibDir + LibSuffix, the
detector could first check the version indicated by this option (if set). And
if it does not find it, go back to the existing system iterating on found
versions.

What do you think of it? If you are interested, I can make a patch adding such
a feature. This would mosty impact lib/Driver/ToolChains.{cpp,h} and Options.td
(plus autoconf/cmake files if there is a new configure option)

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