[benchmark][PowerPC] Rename mftbl to mftb

[stevewan]

Summary

mftb and mftbl are equivalent, yet mftbl is not recognized on AIX. Therefore, rename mftbl to only have mftb.

For extra reference: Linux Kernel Mailing List reference for replacing mftbl with mftb, https://lkml.org/lkml/2020/10/1/1048.

[lebedev.ri]

Please can you submit this upstream first, so it doesn't get lost?

[stevewan]

In D89506#2334012, @lebedev.ri wrote:

Please can you submit this upstream first, so it doesn't get lost?

Upstream patch submitted at https://github.com/google/benchmark/pull/1069.
Status: Merged.

[ldionne]

Fine for libc++.

[stevewan]

Kindly ping.

[lebedev.ri]

Thanks.
Please rebase if nessesary.
Please add an entry to llvm/utils/benchmark/README.llvm and to libcxx/utils/google-benchmark/README.llvm which contains information about cherry-picked commits that are applied on top of the local copy.

[stevewan]

Add information about the cherry-picked commit and contributor.

[lebedev.ri]

Thank you, please feel free to land this.
There's another copy in test-suite, which is not in the monorepo, might be good to also update it too.

[stevewan]

Recover overwritten commits.

[stevewan]

In D89506#2374263, @lebedev.ri wrote:

Thank you, please feel free to land this.
There's another copy in test-suite, which is not in the monorepo, might be good to also update it too.

For records, link to the test-suite patch, https://reviews.llvm.org/D90779.

libcxx/utils/google-benchmark/src/cycleclock.h

 #if defined(__powerpc64__) || defined(__ppc64__)
   int64_t tb;
   asm volatile("mfspr %0, 268" : "=r"(tb));
   return tb;
 #else
   uint32_t tbl, tbu0, tbu1;
   asm volatile(
       "mftbu %0\n"
-      "mftbl %1\n"
+      "mftb %1\n"
       "mftbu %2"
       : "=r"(tbu0), "=r"(tbl), "=r"(tbu1));
   tbl &= -static_cast<int32_t>(tbu0 == tbu1);
   // high 32 bits in tbu1; low 32 bits in tbl  (tbu0 is no longer needed)
   return (static_cast<uint64_t>(tbu1) << 32) | tbl;
 #endif
 #elif defined(__sparc__)
   int64_t tick;

llvm/utils/benchmark/src/cycleclock.h

 #if defined(__powerpc64__) || defined(__ppc64__)
   int64_t tb;
   asm volatile("mfspr %0, 268" : "=r"(tb));
   return tb;
 #else
   uint32_t tbl, tbu0, tbu1;
   asm volatile(
       "mftbu %0\n"
-      "mftbl %1\n"
+      "mftb %1\n"
       "mftbu %2"
       : "=r"(tbu0), "=r"(tbl), "=r"(tbu1));
   tbl &= -static_cast<int32_t>(tbu0 == tbu1);
   // high 32 bits in tbu1; low 32 bits in tbl  (tbu0 is no longer needed)
   return (static_cast<uint64_t>(tbu1) << 32) | tbl;
 #endif
 #elif defined(__sparc__)
   int64_t tick;