X87: [turbofan] Turn Math.clz32 into an inlinable builtin.

src/x87/macro-assembler-x87.cc

Index: src/x87/macro-assembler-x87.cc
diff --git a/src/x87/macro-assembler-x87.cc b/src/x87/macro-assembler-x87.cc
index fc067348e4626ee2e6dd5b2f19a00c03e96af995..b6befebf67ecefe251a4b0446143f17775136898 100644
--- a/src/x87/macro-assembler-x87.cc
+++ b/src/x87/macro-assembler-x87.cc
@@ -2355,6 +2355,17 @@ void MacroAssembler::Move(const Operand& dst, const Immediate& x) {
 }
 
 
+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));