thakis created this revision. thakis added a reviewer: rnk. -no-canonical-prefixes is a weird flag: In gcc, it controls whether realpath() is called on the path of the driver binary. It's needed to support some usecases where gcc is symlinked to, see https://gcc.gnu.org/ml/gcc/2011-01/msg00429.html for some background.
In clang, the resource dir is found relative to the compiler binary, and without -no-canonical-prefixes that's an absolute path. For clang, the main use case for -no-canonical-prefixes is to make the -resource-dir path added by the driver relative instead of absolute. Making it relative seems like the better default, but since neither clang not gcc have -canonical-prefixes without no- which makes changing the default tricky, and since some symlink behaviors do depend on the realpath() call at least for gcc, just expose -no-canonical-prefixes in clang-cl mode. Alternatively we could default to no-canonical-prefix-mode for clang-cl since it's less likely to be used in symlinked scenarios, but since you already need to about -no-canonical-prefixes for the non-clang-cl bits of your build, not hooking this of driver mode seems better to me. https://reviews.llvm.org/D47480 Files: include/clang/Driver/Options.td test/Driver/cl-options.c Index: include/clang/Driver/Options.td =================================================================== --- include/clang/Driver/Options.td +++ include/clang/Driver/Options.td @@ -2251,7 +2251,7 @@ def multiply__defined__unused : Separate<["-"], "multiply_defined_unused">; def multiply__defined : Separate<["-"], "multiply_defined">; def mwarn_nonportable_cfstrings : Flag<["-"], "mwarn-nonportable-cfstrings">, Group<m_Group>; -def no_canonical_prefixes : Flag<["-"], "no-canonical-prefixes">, Flags<[HelpHidden]>, +def no_canonical_prefixes : Flag<["-"], "no-canonical-prefixes">, Flags<[HelpHidden, CoreOption]>, HelpText<"Use relative instead of canonical paths">; def no_cpp_precomp : Flag<["-"], "no-cpp-precomp">, Group<clang_ignored_f_Group>; def no_integrated_cpp : Flag<["-", "--"], "no-integrated-cpp">, Flags<[DriverOption]>; Index: test/Driver/cl-options.c =================================================================== --- test/Driver/cl-options.c +++ test/Driver/cl-options.c @@ -591,6 +591,8 @@ // RUN: -flimit-debug-info \ // RUN: -flto \ // RUN: -fmerge-all-constants \ +// RUN: -no-canonical-prefixes \ +// RUN: -fno-coverage-mapping \ // RUN: --version \ // RUN: -Werror /Zs -- %s 2>&1
Index: include/clang/Driver/Options.td =================================================================== --- include/clang/Driver/Options.td +++ include/clang/Driver/Options.td @@ -2251,7 +2251,7 @@ def multiply__defined__unused : Separate<["-"], "multiply_defined_unused">; def multiply__defined : Separate<["-"], "multiply_defined">; def mwarn_nonportable_cfstrings : Flag<["-"], "mwarn-nonportable-cfstrings">, Group<m_Group>; -def no_canonical_prefixes : Flag<["-"], "no-canonical-prefixes">, Flags<[HelpHidden]>, +def no_canonical_prefixes : Flag<["-"], "no-canonical-prefixes">, Flags<[HelpHidden, CoreOption]>, HelpText<"Use relative instead of canonical paths">; def no_cpp_precomp : Flag<["-"], "no-cpp-precomp">, Group<clang_ignored_f_Group>; def no_integrated_cpp : Flag<["-", "--"], "no-integrated-cpp">, Flags<[DriverOption]>; Index: test/Driver/cl-options.c =================================================================== --- test/Driver/cl-options.c +++ test/Driver/cl-options.c @@ -591,6 +591,8 @@ // RUN: -flimit-debug-info \ // RUN: -flto \ // RUN: -fmerge-all-constants \ +// RUN: -no-canonical-prefixes \ +// RUN: -fno-coverage-mapping \ // RUN: --version \ // RUN: -Werror /Zs -- %s 2>&1
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