[X86] Set isMovImm for some X86 instructions

[sanjoy]

Summary

This makes MI->isMoveImmediate() return true for the right instructions.
This is *not* an NFC since the PeepholeOptimizer pass uses this, and it
looks like the x86 backend runs PeepholeOptimizer (but no X86 test
breaks after this change).

Ideas on how to test this (or a justification for why this is NFC! :) )
will be appreciated.

[MatzeB]

Glancing at the peephole optimizer code, isMoveImm is checked to figure out early whether TargetInstrInfo::FoldImmediate() will have any effect later. Seeing that X86 doesn't implement that function I would assume this patch to be pointless. (Or maybe we should implement FoldImmediate()?)

[sanjoy]

I didn't end up needing this.

lib/Target/X86/X86InstrInfo.td

 def MOV16rr : I<0x89, MRMDestReg, (outs GR16:$dst), (ins GR16:$src),
                 "mov{w}\t{$src, $dst|$dst, $src}", [], IIC_MOV>, OpSize16;
 def MOV32rr : I<0x89, MRMDestReg, (outs GR32:$dst), (ins GR32:$src),
                 "mov{l}\t{$src, $dst|$dst, $src}", [], IIC_MOV>, OpSize32;
 def MOV64rr : RI<0x89, MRMDestReg, (outs GR64:$dst), (ins GR64:$src),
                  "mov{q}\t{$src, $dst|$dst, $src}", [], IIC_MOV>;
 }
 
-let isReMaterializable = 1, isAsCheapAsAMove = 1 in {
+let isReMaterializable = 1, isAsCheapAsAMove = 1, isMoveImm = 1 in {
 def MOV8ri  : Ii8 <0xB0, AddRegFrm, (outs GR8 :$dst), (ins i8imm :$src),
                    "mov{b}\t{$src, $dst|$dst, $src}",
                    [(set GR8:$dst, imm:$src)], IIC_MOV>;
 def MOV16ri : Ii16<0xB8, AddRegFrm, (outs GR16:$dst), (ins i16imm:$src),
                    "mov{w}\t{$src, $dst|$dst, $src}",
                    [(set GR16:$dst, imm:$src)], IIC_MOV>, OpSize16;
 def MOV32ri : Ii32<0xB8, AddRegFrm, (outs GR32:$dst), (ins i32imm:$src),
                    "mov{l}\t{$src, $dst|$dst, $src}",
                    [(set GR32:$dst, imm:$src)], IIC_MOV>, OpSize32;
 def MOV64ri32 : RIi32S<0xC7, MRM0r, (outs GR64:$dst), (ins i64i32imm:$src),
                        "mov{q}\t{$src, $dst|$dst, $src}",
                        [(set GR64:$dst, i64immSExt32:$src)], IIC_MOV>;
 }
-let isReMaterializable = 1 in {
+let isReMaterializable = 1, isMoveImm = 1 in {
 def MOV64ri : RIi64<0xB8, AddRegFrm, (outs GR64:$dst), (ins i64imm:$src),
                     "movabs{q}\t{$src, $dst|$dst, $src}",
                     [(set GR64:$dst, imm:$src)], IIC_MOV>;
 }
 
 // Longer forms that use a ModR/M byte. Needed for disassembler
 let isCodeGenOnly = 1, ForceDisassemble = 1, hasSideEffects = 0 in {
 def MOV8ri_alt  : Ii8 <0xC6, MRM0r, (outs GR8 :$dst), (ins i8imm :$src),