[compiler-rt][builtins] Provide __clear_cache for SPARC

[ro]

Summary

While working on https://reviews.llvm.org/D40900 (which now is effectively about
enabling compiler-rt on sparc in general, two tests were failing since __clear_cache
aborted. While libgcc's __clear_cache is just empty, this only happens because
gcc ( in gcc/config/sparc/sparc.c (sparc32_initialize_trampoline, sparc64_initialize_trampoline)
emits flush insns directly.

The following patch mimics that.

Tested on sparcv9-sun-solaris2.11. Ok for trunk?

[ro]

Ping? It's been a week.

[ro]

Ping^2? Two weeks now; anyone else who could review this?

[jyknight]

The code you reference in GCC is only for trampolines, while this function is used to implement builtin_clear_cache. AFAICT GCC is just wrong to implement this as a no-op.

Anyways, looks OK.

[ro]

In D64496#1597361, @jyknight wrote:

The code you reference in GCC is only for trampolines, while this function is used to implement builtin_clear_cache. AFAICT GCC is just wrong to implement this as a no-op.

I think you're right: I missed the __builtin___clear_cache part on the GCC side. I'll file a GCC PR for the issue. Thanks.

compiler-rt/trunk/lib/builtins/clear_cache.c

#elif defined(__powerpc64__)
 
   for (uintptr_t line = start_line; line < end_line; line += line_size)
     __asm__ volatile("dcbf 0, %0" : : "r"(line));
   __asm__ volatile("sync");
 
   for (uintptr_t line = start_line; line < end_line; line += line_size)
     __asm__ volatile("icbi 0, %0" : : "r"(line));
   __asm__ volatile("isync");
+#elif defined(__sparc__)
+  const size_t dword_size = 8;
+  const size_t len = (uintptr_t)end - (uintptr_t)start;
+
+  const uintptr_t mask = ~(dword_size - 1);
+  const uintptr_t start_dword = ((uintptr_t)start) & mask;
+  const uintptr_t end_dword = ((uintptr_t)start + len + dword_size - 1) & mask;
+
+  for (uintptr_t dword = start_dword; dword < end_dword; dword += dword_size)
+    __asm__ volatile("flush %0" : : "r"(dword));
 #else
 #if __APPLE__
   // On Darwin, sys_icache_invalidate() provides this functionality
   sys_icache_invalidate(start, end - start);
 #else
   compilerrt_abort();
 #endif
 #endif
 }