[turbofan] Turn Math.clz32 into an inlinable builtin.

src/ia32/macro-assembler-ia32.cc

Index: src/ia32/macro-assembler-ia32.cc
diff --git a/src/ia32/macro-assembler-ia32.cc b/src/ia32/macro-assembler-ia32.cc
index 52e674f9dc035a991b0356ab72148c2a60447f56..365ad3cc0ef40c58313058bca7d9949967196414 100644
--- a/src/ia32/macro-assembler-ia32.cc
+++ b/src/ia32/macro-assembler-ia32.cc
@@ -2466,6 +2466,17 @@ void MacroAssembler::Pinsrd(XMMRegister dst, const Operand& src, int8_t imm8) {
 }
 
 
+void MacroAssembler::Lzcnt(Register dst, const Operand& src) {
+  // TODO(intel): Add support for LZCNT (with ABM/BMI1).
+  Label not_zero_src;
+  bsr(dst, src);
+  j(not_zero, &not_zero_src, Label::kNear);
+  Move(dst, Immediate(63));  // 63^31 == 32
+  bind(&not_zero_src);
+  xor_(dst, Immediate(31));  // for x in [0..31], 31^x == 31-x.
+}
+
+
 void MacroAssembler::SetCounter(StatsCounter* counter, int value) {
   if (FLAG_native_code_counters && counter->Enabled()) {
     mov(Operand::StaticVariable(ExternalReference(counter)), Immediate(value));