[Mips] Reserve hardware register HWR2 (llvm#127775)

Fix pr llvm#127553.
x86_64 failed to run readcyclecounter.ll when enable expensive_check,
it would error "Using an undefined physical register".

Author: yingopq

llvm/lib/Target/Mips/MipsRegisterInfo.cpp

@@ -207,6 +207,7 @@ getReservedRegs(const MachineFunction &MF) const {
 
   // Reserve hardware registers.
   Reserved.set(Mips::HWR29);
+  Reserved.set(Mips::HWR2);
 
   // Reserve DSP control register.
   Reserved.set(Mips::DSPPos);

llvm/test/CodeGen/Mips/readcyclecounter.ll

@@ -7,8 +7,6 @@
 ;RUN: llc -mtriple=mipsel -mcpu=mips2 < %s | FileCheck %s --check-prefix=MIPSEL_NOT_SUPPORTED
 ;RUN: llc -mtriple=mips64el -mcpu=mips3 < %s | FileCheck %s --check-prefix=MIPS64EL_NOT_SUPPORTED
 
-; XFAIL: expensive_checks
-
 declare i64 @llvm.readcyclecounter() nounwind readnone
 
 define i64 @test_readcyclecounter() nounwind {