[mips] Disable code generation through FastISel for MIPS32R6.

[dsanders]

LGTM

lib/Target/Mips/MipsFastISel.cpp

public:
   // Backend specific FastISel code.
   explicit MipsFastISel(FunctionLoweringInfo &funcInfo,
                         const TargetLibraryInfo *libInfo)
       : FastISel(funcInfo, libInfo), TM(funcInfo.MF->getTarget()),
         Subtarget(&funcInfo.MF->getSubtarget<MipsSubtarget>()),
         TII(*Subtarget->getInstrInfo()), TLI(*Subtarget->getTargetLowering()) {
     MFI = funcInfo.MF->getInfo<MipsFunctionInfo>();
     Context = &funcInfo.Fn->getContext();
+    bool ISASupported = !Subtarget->hasMips32r6() && Subtarget->hasMips32();
     TargetSupported =
-        ((TM.getRelocationModel() == Reloc::PIC_) &&
-         ((Subtarget->hasMips32r2() || Subtarget->hasMips32()) &&
-          (static_cast<const MipsTargetMachine &>(TM).getABI().IsO32())));
+        ISASupported && (TM.getRelocationModel() == Reloc::PIC_) &&
+        (static_cast<const MipsTargetMachine &>(TM).getABI().IsO32());
     UnsupportedFPMode = Subtarget->isFP64bit();
   }
 
   unsigned fastMaterializeAlloca(const AllocaInst *AI) override;
   unsigned fastMaterializeConstant(const Constant *C) override;
   bool fastSelectInstruction(const Instruction *I) override;
 
 #include "MipsGenFastISel.inc"

test/CodeGen/Mips/Fast-ISel/check-disabled-mcpus.ll

+; RUN: llc -march=mips -mcpu=mips2 -O0 -relocation-model=pic \
+; RUN:     -fast-isel-verbose <%s 2>&1 | FileCheck %s
+; RUN: llc -march=mips -mcpu=mips3 -O0 -relocation-model=pic \
+; RUN:     -fast-isel-verbose <%s 2>&1 | FileCheck %s
+; RUN: llc -march=mips -mcpu=mips4 -O0 -relocation-model=pic \
+; RUN:     -fast-isel-verbose <%s 2>&1 | FileCheck %s
+
+; RUN: llc -march=mips -mcpu=mips32r6 -O0 -relocation-model=pic \
+; RUN:     -fast-isel-verbose <%s 2>&1 | FileCheck %s
+
+; RUN: llc -march=mips -mcpu=mips64 -O0 -relocation-model=pic \
+; RUN:     -fast-isel-verbose <%s 2>&1 | FileCheck %s
+; RUN: llc -march=mips -mcpu=mips64r2 -O0 -relocation-model=pic \
+; RUN:     -fast-isel-verbose <%s 2>&1 | FileCheck %s
+; RUN: llc -march=mips -mcpu=mips64r3 -O0 -relocation-model=pic \
+; RUN:     -fast-isel-verbose <%s 2>&1 | FileCheck %s
+; RUN: llc -march=mips -mcpu=mips64r5 -O0 -relocation-model=pic \
+; RUN:     -fast-isel-verbose <%s 2>&1 | FileCheck %s
+; RUN: llc -march=mips -mcpu=mips32r6 -O0 -relocation-model=pic \
+; RUN:     -fast-isel-verbose <%s 2>&1 | FileCheck %s
+
+; CHECK: FastISel missed terminator:   ret i32 0
+
+define i32 @foo() {
+entry:
+  ret i32 0
+}