[OSX][TargetLibraryInfo] Mark memrchr as unavailable on OSX

[kpdev42]

Summary

On Mac OSX (tested version macOS 12.4, sdk 12.1) llvm can replace call to strrchr() with call to memrchr() when string length is known at compile time. This results in link error, because memrchr is not present in libSystem. It is needed to disable this optimization in TargetLibraryInfo for affected OSX versions.

This non-standard function (memrchr) is not present on (at least) several versions of MacOS https://www.gnu.org/software/gnulib/manual/html_node/memrchr.html , so, in this patch memrchr is marked as unavailable for all versions. If someone knows versions where it should be available - please let me know.

Github issue: https://github.com/llvm/llvm-project/issues/62254

Tests for this feature also cannot be easily added: https://reviews.llvm.org/D134134#3801747

~~~

Huawei RRI, OS Lab

[nikic]

Tests for this feature also cannot be easily added: https://reviews.llvm.org/D134134#3801747

You should be able to test that InstCombine does not perform the strrchr -> memrchr fold if a macos triple is given.

llvm/lib/Analysis/TargetLibraryInfo.cpp

206

Isn't this supposed to be memrchr?

[kpdev42]

Fix typo (memchr -> memrchr)

[kpdev42]

llvm/lib/Analysis/TargetLibraryInfo.cpp

206

Thank you, fixed

[kpdev42]

In D155168#4496699, @nikic wrote:

Tests for this feature also cannot be easily added: https://reviews.llvm.org/D134134#3801747

You should be able to test that InstCombine does not perform the strrchr -> memrchr fold if a macos triple is given.

Ok, will add it

[mohd-akram]

@nikic Is this good to merge? This issue is present in LLVM 15 and 16 is breaking packages that use strrchr on macOS with a cryptic error (see eg. https://github.com/macports/macports-ports/pull/19868). Hopefully this can be merged before LLVM 17 is released.

[nikic]

LGTM

[kpdev42]

@nikic @mohd-akram Thank you for the review

llvm/lib/Analysis/TargetLibraryInfo.cpp

static void initialize(TargetLibraryInfoImpl &TLI, const Triple &T,
   // memset_pattern{4,8,16} is only available on iOS 3.0 and Mac OS X 10.5 and
   // later. All versions of watchOS support it.
   if (T.isMacOSX()) {
     // available IO unlocked variants on Mac OS X
     TLI.setAvailable(LibFunc_getc_unlocked);
     TLI.setAvailable(LibFunc_getchar_unlocked);
     TLI.setAvailable(LibFunc_putc_unlocked);
     TLI.setAvailable(LibFunc_putchar_unlocked);
+    TLI.setUnavailable(LibFunc_memrchr);
 
     if (T.isMacOSXVersionLT(10, 5)) {
       TLI.setUnavailable(LibFunc_memset_pattern4);
       TLI.setUnavailable(LibFunc_memset_pattern8);
       TLI.setUnavailable(LibFunc_memset_pattern16);
     }
   } else if (T.isiOS()) {
     if (T.isOSVersionLT(3, 0)) {