Fix Android clear_cache ASM

[compnerd]

This seems incorrect. There is an argument to the call. Why do you think that this change is needed?

[angelsl]

In D14115#276198, @compnerd wrote:

This seems incorrect. There is an argument to the call. Why do you think that this change is needed?

.../build/src/compiler-rt/lib/builtins/clear_cache.c: In function '__clear_cache':
.../build/src/compiler-rt/lib/builtins/clear_cache.c:106:9: error: asm-specifier for variable 'start_reg' conflicts with asm clobber list
         __asm __volatile("svc 0x0" : "=r"(start_reg)
         ^
.../build/src/compiler-rt/lib/builtins/clear_cache.c:106:9: error: asm-specifier for variable 'start_reg' conflicts with asm clobber list
.../build/obj/arm-linux-androideabi/rt/compiler-rt/triple/builtins/armv7/SubDir.lib__builtins/clear_cache.o] Error 1

I believe the compiler takes into account r0 being changed/clobbered, since it's already in the output register list.

[compnerd]

Ah, wrapping on a phone made it look like you were modifying the input parameters, not the clobbers list. What are you seeing that error with? Ive not seen it with clang nor gcc.

[angelsl]

In D14115#276229, @compnerd wrote:

Ah, wrapping on a phone made it look like you were modifying the input parameters, not the clobbers list. What are you seeing that error with? Ive not seen it with clang nor gcc.

GCC 4.8 in the Android NDK.

The person who made this change reportedly made it after it failed on Clang too. Not sure exactly. I'll try with Clang.

[angelsl]

Clang 3.7 compiles the version GCC rejects fine.

But even with the clobber list removed, the output assembly is identical.

[angelsl]

Would appreciate if someone took a look at this. Thanks.

[angelsl]

Would appreciate it if someone reviewed this.

[compnerd]

Seems that gcc 5.3.0 also will warn about this. Since this shouldn't effect the output, I think that this should be safe enough to merge.

[angelsl]

Please help me commit this. Thanks.

[compnerd]

SVN r261821.

lib/builtins/clear_cache.c

          const register int flags __asm("r2") = 0;
          const register int syscall_nr __asm("r7") = __ARM_NR_cacheflush;
         __asm __volatile("svc 0x0" : "=r"(start_reg)
-            : "r"(syscall_nr), "r"(start_reg), "r"(end_reg), "r"(flags) : "r0");
+            : "r"(syscall_nr), "r"(start_reg), "r"(end_reg), "r"(flags));
          if (start_reg != 0) {
              compilerrt_abort();
          }