[mips][microMIPS] Change register class for GP register

[zoran.jovanovic]

Summary

In order to fix issues with "invalid operand" in microMIPS 16 bit instructions register class of GP register must be changed to GPRMM16RegClass.

[sstankovic]

LGTM

llvm/trunk/lib/Target/Mips/MipsMachineFunction.cpp

bool MipsFunctionInfo::globalBaseRegSet() const {
   return GlobalBaseReg;
 }
 
 unsigned MipsFunctionInfo::getGlobalBaseReg() {
   // Return if it has already been initialized.
   if (GlobalBaseReg)
     return GlobalBaseReg;
 
+  MipsSubtarget const &STI =
+      static_cast<const MipsSubtarget &>(MF.getSubtarget());
+
   const TargetRegisterClass *RC =
-      static_cast<const MipsSubtarget &>(MF.getSubtarget()).inMips16Mode()
+      STI.inMips16Mode()
           ? &Mips::CPU16RegsRegClass
+          : STI.inMicroMipsMode()
+                ? &Mips::GPRMM16RegClass
                 : static_cast<const MipsTargetMachine &>(MF.getTarget())
                           .getABI()
                           .IsN64()
                       ? &Mips::GPR64RegClass
                       : &Mips::GPR32RegClass;
   return GlobalBaseReg = MF.getRegInfo().createVirtualRegister(RC);
 }
 
 bool MipsFunctionInfo::mips16SPAliasRegSet() const {
   return Mips16SPAliasReg;
 }
 unsigned MipsFunctionInfo::getMips16SPAliasReg() {
   // Return if it has already been initialized.

llvm/trunk/test/CodeGen/Mips/micromips-gp-rc.ll

+; RUN: llc -march=mipsel -mcpu=mips32r2 -mattr=+micromips \
+; RUN:   -relocation-model=pic -O3 < %s | FileCheck %s
+
+@g = external global i32
+
+; Function Attrs: noreturn nounwind
+define void @foo() #0 {
+entry:
+  %0 = load i32* @g, align 4
+  tail call void @exit(i32 signext %0)
+  unreachable
+}
+
+; Function Attrs: noreturn
+declare void @exit(i32 signext)
+
+; CHECK: move $gp, ${{[0-9]+}}
+