ARM: Be more smart about switching instructions when immediates...

src/utils.h

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 29 matching lines @@
 #define IS_POWER_OF_TWO(x) (((x) & ((x) - 1)) == 0)
 
 // Returns true iff x is a power of 2 (or zero). Cannot be used with the
 // maximally negative value of the type T (the -1 overflows).
 template <typename T>
 static inline bool IsPowerOf2(T x) {
   return IS_POWER_OF_TWO(x);
 }
 
 
+// X must be a power of 2.  Returns the number of trailing zeros.
+template <typename T>
+static inline int WhichPowerOf2(T x) {

[Søren Thygesen Gjesse, 2010/06/14 07:56:47]

Shouldn't there be a test case for this?

[Erik Corry, 2010/06/14 21:05:46]

Assert added.

+  ASSERT(IsPowerOf2(x));
+  if (x < 0) return 31;
+  if (x == 0) return 32;
+  int bits = 0;
+  if (x >= 0x10000) {
+    bits += 16;
+    x >>= 16;
+  }
+  if (x >= 0x100) {
+    bits += 8;
+    x >>= 8;
+  }
+  if (x >= 0x10) {
+    bits += 4;
+    x >>= 4;
+  }
+  switch (x) {
+    case 1: return bits;
+    case 2: return bits + 1;
+    case 4: return bits + 2;
+    case 8: return bits + 3;
+    default: UNREACHABLE();
+  }
+  return 0;
+}
+
+
 // The C++ standard leaves the semantics of '>>' undefined for
 // negative signed operands. Most implementations do the right thing,
 // though.
 static inline int ArithmeticShiftRight(int x, int s) {
   return x >> s;
 }
 
 
 // Compute the 0-relative offset of some absolute value x of type T.
 // This allows conversion of Addresses and integral types into
@@ skipping 641 matching lines @@
 
   Dest dest;
   memcpy(&dest, &source, sizeof(dest));
   return dest;
 }
 
 } }  // namespace v8::internal
 
 
 #endif  // V8_UTILS_H_