MIPS: Fixing illegal use of at register

src/mips64/assembler-mips64.cc

Index: src/mips64/assembler-mips64.cc
diff --git a/src/mips64/assembler-mips64.cc b/src/mips64/assembler-mips64.cc
index a7a8d6d511d22c9f1e00dce5af4b46e583dbe269..5837e6dcf96454af0e3f720f96e14e6d573f76e3 100644
--- a/src/mips64/assembler-mips64.cc
+++ b/src/mips64/assembler-mips64.cc
@@ -2378,6 +2378,7 @@ void Assembler::lwc1(FPURegister fd, const MemOperand& src) {
 
 
 void Assembler::ldc1(FPURegister fd, const MemOperand& src) {
+  DCHECK(!src.rm().is(at));
   if (is_int16(src.offset_)) {
     GenInstrImmediate(LDC1, src.rm(), fd, src.offset_);
   } else {  // Offset > 16 bits, use multiple instructions to load.
@@ -2398,6 +2399,7 @@ void Assembler::swc1(FPURegister fd, const MemOperand& src) {
 
 
 void Assembler::sdc1(FPURegister fd, const MemOperand& src) {
+  DCHECK(!src.rm().is(at));
   if (is_int16(src.offset_)) {
     GenInstrImmediate(SDC1, src.rm(), fd, src.offset_);
   } else {  // Offset > 16 bits, use multiple instructions to load.