[reg] Add RegisterBase::TakeAny(RegList*) helper

The helper function removes a register from the list and returns it

Bug: v8:7700
Change-Id: I3f9fe9d30113b9e6c7362dc8443e39ae3d1adf07
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3488372Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79284}

src/codegen/register.h

@@ -5,6 +5,7 @@
 #ifndef V8_CODEGEN_REGISTER_H_
 #define V8_CODEGEN_REGISTER_H_
 
+#include "src/base/bits.h"
 #include "src/base/bounds.h"
 #include "src/codegen/reglist.h"
 
@@ -53,6 +54,13 @@ class RegisterBase {
     return is_valid() ? RegList{1} << code() : RegList{};
   }
 
+  static constexpr SubType TakeAny(RegList* list) {
+    RegList& value = *list;
+    SubType result = from_code(base::bits::CountTrailingZerosNonZero(value));
+    *list = value & (value - 1);
+    return result;
+  }
+
   inline constexpr bool operator==(SubType other) const {
     return reg_code_ == other.reg_code_;
   }

src/codegen/reglist.h

@@ -20,6 +20,8 @@ using RegList = uint64_t;
 using RegList = uint32_t;
 #endif
 
+constexpr RegList kEmptyRegList = 0;
+
 // Get the number of registers in a given register list.
 constexpr int NumRegs(RegList list) {
   return base::bits::CountPopulation(list);

src/maglev/maglev-ir.cc

@@ -497,8 +497,8 @@ void CheckMaps::GenerateCode(MaglevCodeGenState* code_gen_state,
                              const ProcessingState& state) {
   Register object = ToRegister(actual_map_input());
   RegList temps = temporaries();
-  Register map_tmp =
-      Register::from_code(base::bits::CountTrailingZerosNonZero(temps));
+  Register map_tmp = Register::TakeAny(&temps);
+  DCHECK_EQ(kEmptyRegList, temps);
 
   __ LoadMap(map_tmp, object);
   __ Cmp(map_tmp, map().object());