Remove volatile from variables to improve performance

BUG=libyuv:703
TEST=compile and disassemble.  see registers used not stack.
R=wangcheng@google.com

Change-Id: Iaa07ee5d0c35252994491bb2868276e161149efd
Reviewed-on: https://chromium-review.googlesource.com/500427
Commit-Queue: Frank Barchard <fbarchard@google.com>
Reviewed-by: Cheng Wang <wangcheng@google.com>

source/compare_common.cc

@@ -19,7 +19,7 @@ extern "C" {
 
 #if ORIGINAL_C
 uint32 HammingDistance_C(const uint8* src_a, const uint8* src_b, int count) {
-  volatile uint32 diff = 0u;
+  uint32 diff = 0u;
 
   int i;
   for (i = 0; i < count; ++i) {
@@ -39,7 +39,7 @@ uint32 HammingDistance_C(const uint8* src_a, const uint8* src_b, int count) {
 
 // Hakmem method for hamming distance.
 uint32 HammingDistance_C(const uint8* src_a, const uint8* src_b, int count) {
-  volatile uint32 diff = 0u;
+  uint32 diff = 0u;
 
   int i;
   for (i = 0; i < count - 3; i += 4) {

source/compare_gcc.cc

@@ -23,7 +23,7 @@ extern "C" {
     (defined(__x86_64__) || (defined(__i386__) && !defined(_MSC_VER)))
 
 uint32 HammingDistance_X86(const uint8* src_a, const uint8* src_b, int count) {
-  volatile uint32 diff = 0u;
+  uint32 diff = 0u;
 
   int i;
   for (i = 0; i < count - 7; i += 8) {

source/compare_neon.cc

@@ -22,7 +22,7 @@ extern "C" {
     !defined(__aarch64__)
 
 uint32 SumSquareError_NEON(const uint8* src_a, const uint8* src_b, int count) {
-  volatile uint32 sse;
+  uint32 sse;
   asm volatile (
     "vmov.u8    q8, #0                         \n"
     "vmov.u8    q10, #0                        \n"

source/compare_neon64.cc

@@ -22,7 +22,7 @@ extern "C" {
 
 #if 0
 uint32 HammingDistance_NEON(const uint8* src_a, const uint8* src_b, int count) {
-  volatile uint32 diff;
+  uint32 diff;
   asm volatile (
     "eor        v4.16b, v4.16b, v4.16b         \n"
     "eor        v5.16b, v5.16b, v5.16b         \n"
@@ -51,7 +51,7 @@ uint32 HammingDistance_NEON(const uint8* src_a, const uint8* src_b, int count) {
 #endif
 
 uint32 HammingDistance_NEON(const uint8* src_a, const uint8* src_b, int count) {
-  volatile uint32 diff;
+  uint32 diff;
   asm volatile (
     "movi       d6, #0                         \n"
 
@@ -82,7 +82,7 @@ uint32 HammingDistance_NEON(const uint8* src_a, const uint8* src_b, int count) {
 }
 
 uint32 SumSquareError_NEON(const uint8* src_a, const uint8* src_b, int count) {
-  volatile uint32 sse;
+  uint32 sse;
   asm volatile (
     "eor        v16.16b, v16.16b, v16.16b      \n"
     "eor        v18.16b, v18.16b, v18.16b      \n"