[asan] Remove unnecessary spill in optimized callbacks

[vitalybuka]

Summary

We can use r11 scratch registers for calculations.

It does not result in any performance improvements, as the spill is on
the slow path of partial granules.

See X86AsmPrinter::LowerASAN_CHECK_MEMACCESS for callers.

compiler-rt/lib/asan/asan_rtl_x86_64.S

#define ASAN_MEMORY_ACCESS_INITIAL_CHECK_ADD(reg, op, s) \
         movsbl ASAN_SHADOW_OFFSET_CONST(%r10),%r10d ;\
         test   %r10d,%r10d ;\
         jne    CLABEL(reg, op, s, add) ;\
 RLABEL(reg, op, s, add): ;\
         retq  ;\
 
 #define ASAN_MEMORY_ACCESS_EXTRA_CHECK_1(reg, op, i) \
 CLABEL(reg, op, 1, i): ;\
-        push   %rcx ;\
-        mov    %##reg,%rcx ;\
-        and    $0x7,%ecx ;\
-        cmp    %r10d,%ecx ;\
-        pop    %rcx ;\
+        mov    %##reg,%r11 ;\
+        and    $0x7,%r11d ;\
+        cmp    %r10d,%r11d ;\
         jl     RLABEL(reg, op, 1, i);\
         mov    %##reg,%rdi ;\
         jmp    __asan_report_##op##1_asm ;\
 
 #define ASAN_MEMORY_ACCESS_EXTRA_CHECK_2(reg, op, i) \
 CLABEL(reg, op, 2, i): ;\
-        push   %rcx ;\
-        mov    %##reg,%rcx ;\
-        and    $0x7,%ecx ;\
-        add    $0x1,%ecx ;\
-        cmp    %r10d,%ecx ;\
-        pop    %rcx ;\
+        mov    %##reg,%r11 ;\
+        and    $0x7,%r11d ;\
+        add    $0x1,%r11d ;\
+        cmp    %r10d,%r11d ;\
         jl     RLABEL(reg, op, 2, i);\
         mov    %##reg,%rdi ;\
         jmp    __asan_report_##op##2_asm ;\
 
 #define ASAN_MEMORY_ACCESS_EXTRA_CHECK_4(reg, op, i) \
 CLABEL(reg, op, 4, i): ;\
-        push   %rcx ;\
-        mov    %##reg,%rcx ;\
-        and    $0x7,%ecx ;\
-        add    $0x3,%ecx ;\
-        cmp    %r10d,%ecx ;\
-        pop    %rcx ;\
+        mov    %##reg,%r11 ;\
+        and    $0x7,%r11d ;\
+        add    $0x3,%r11d ;\
+        cmp    %r10d,%r11d ;\
         jl     RLABEL(reg, op, 4, i);\
         mov    %##reg,%rdi ;\
         jmp    __asan_report_##op##4_asm ;\
 
 #define ASAN_MEMORY_ACCESS_CALLBACK_ADD_1(reg, op) \
 BEGINF(reg, op, 1, add) ;\
         ASAN_MEMORY_ACCESS_INITIAL_CHECK_ADD(reg, op, 1) ;\
         ASAN_MEMORY_ACCESS_EXTRA_CHECK_1(reg, op, add) ;\