Bug 1664045: Relax register constraints for MWasmCompareExchangeI64 o…

…n x86; r=lth

Not using atStart makes the live ranges bigger than they ought to be; the
inputs must be only be used at the use position for the instruction, not the
def use position.

Differential Revision: https://phabricator.services.mozilla.com/D91602

js/src/jit/x86/Lowering-x86.cpp

@@ -410,9 +410,9 @@ void LIRGenerator::visitWasmCompareExchangeHeap(MWasmCompareExchangeHeap* ins) {
 
   if (ins->access().type() == Scalar::Int64) {
     auto* lir = new (alloc()) LWasmCompareExchangeI64(
-        useRegister(memoryBase), useRegister(base),
-        useInt64Fixed(ins->oldValue(), Register64(edx, eax)),
-        useInt64Fixed(ins->newValue(), Register64(ecx, ebx)));
+        useRegisterAtStart(memoryBase), useRegisterAtStart(base),
+        useInt64FixedAtStart(ins->oldValue(), Register64(edx, eax)),
+        useInt64FixedAtStart(ins->newValue(), Register64(ecx, ebx)));
     defineInt64Fixed(lir, ins,
                      LInt64Allocation(LAllocation(AnyRegister(edx)),
                                       LAllocation(AnyRegister(eax))));