[bits] Make bit rotation branchless

A minor optimization to the four bit rotation functions.

Drive-by: Make them constexpr.

R=ahaas@chromium.org

Bug: v8:9810
Change-Id: Ic563310030aa487f976017032291a553705d1ec2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1903972Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64854}

src/base/bits.h

@@ -182,30 +182,25 @@ inline uint32_t RoundDownToPowerOfTwo32(uint32_t value) {
 
 
 // Precondition: 0 <= shift < 32
-inline uint32_t RotateRight32(uint32_t value, uint32_t shift) {
-  if (shift == 0) return value;
-  return (value >> shift) | (value << (32 - shift));
+inline constexpr uint32_t RotateRight32(uint32_t value, uint32_t shift) {
+  return (value >> shift) | (value << ((32 - shift) & 31));
 }
 
 // Precondition: 0 <= shift < 32
-inline uint32_t RotateLeft32(uint32_t value, uint32_t shift) {
-  if (shift == 0) return value;
-  return (value << shift) | (value >> (32 - shift));
+inline constexpr uint32_t RotateLeft32(uint32_t value, uint32_t shift) {
+  return (value << shift) | (value >> ((32 - shift) & 31));
 }
 
 // Precondition: 0 <= shift < 64
-inline uint64_t RotateRight64(uint64_t value, uint64_t shift) {
-  if (shift == 0) return value;
-  return (value >> shift) | (value << (64 - shift));
+inline constexpr uint64_t RotateRight64(uint64_t value, uint64_t shift) {
+  return (value >> shift) | (value << ((64 - shift) & 63));
 }
 
 // Precondition: 0 <= shift < 64
-inline uint64_t RotateLeft64(uint64_t value, uint64_t shift) {
-  if (shift == 0) return value;
-  return (value << shift) | (value >> (64 - shift));
+inline constexpr uint64_t RotateLeft64(uint64_t value, uint64_t shift) {
+  return (value << shift) | (value >> ((64 - shift) & 63));
 }
 
-
 // SignedAddOverflow32(lhs,rhs,val) performs a signed summation of |lhs| and
 // |rhs| and stores the result into the variable pointed to by |val| and
 // returns true if the signed summation resulted in an overflow.