PPC: smi test optimization

R=mbrandy@us.ibm.com, michael_dawson@ca.ibm.com
BUG=

Review URL: https://codereview.chromium.org/1177263002

Cr-Commit-Position: refs/heads/master@{#28960}

src/ppc/macro-assembler-ppc.h

@@ -1063,11 +1063,16 @@ class MacroAssembler : public Assembler {
     DCHECK(rangeStart >= rangeEnd && rangeStart < kBitsPerPointer);
     int rotate = (rangeEnd == 0) ? 0 : kBitsPerPointer - rangeEnd;
     int width = rangeStart - rangeEnd + 1;
+    if (rc == SetRC && rangeEnd == 0 && width <= 16) {
+      andi(dst, src, Operand((1 << width) - 1));
+    } else {
 #if V8_TARGET_ARCH_PPC64
-    rldicl(dst, src, rotate, kBitsPerPointer - width, rc);
+      rldicl(dst, src, rotate, kBitsPerPointer - width, rc);
 #else
-    rlwinm(dst, src, rotate, kBitsPerPointer - width, kBitsPerPointer - 1, rc);
+      rlwinm(dst, src, rotate, kBitsPerPointer - width, kBitsPerPointer - 1,
+             rc);
 #endif
+    }
   }
 
   inline void ExtractBit(Register dst, Register src, uint32_t bitNumber,