[M68k][MC] Make immediate operands relocatable

[myhsu]

Summary

Sometimes memory addresses are treated as immediate values. Thus immediate operands have to be relocatable.

[myhsu]

With this patch we need a custom decoder for 32-bit immediate value or disassembler won't be able to recognize the correct word ordering. I will add custom decoder support for variable length instruction in separate patches.

[myhsu]

With D142079 and D142080 we can finally decode immediates of all sizes in the correct way.

[0x59616e]

This amazing work LGTM. Thanks !

llvm/lib/Target/M68k/M68kInstrFormats.td

 
 class MxEncAddrMode_i<string opnd_name, int size> : MxEncMemOp {
   let EA = (descend /*MODE*/0b111,
                      /*REGISTER*/0b100);
 
   // Immediate
   let Supplement =
     !cond(
-      !eq(size, 8)  : (descend 0b00000000, (operand "$"#opnd_name, 8)),
-      !eq(size, 16) : (operand "$"#opnd_name, 16),
-      !eq(size, 32) : (ascend (slice "$"#opnd_name, 31, 16),
-                              (slice "$"#opnd_name, 15, 0))
+      !eq(size, 8)  : (descend 0b00000000, (operand "$"#opnd_name, 8,
+                     (encoder "encodeRelocImm<8>"))),
+      !eq(size, 16) : (operand "$"#opnd_name, 16,
+                           (encoder "encodeRelocImm<16>")),
+      !eq(size, 32) : (operand "$"#opnd_name, 32,
+                           (encoder "encodeRelocImm<32>"),
+                           (decoder "DecodeImm32"))
     );
 }
 
 // abs.W -> size_w_l = false
 // abs.L -> size_w_l = true
 class MxEncAddrMode_abs<string opnd_name, bit size_w_l = false> : MxEncMemOp {
   let EA = (descend /*MODE*/0b111,
                     // Wrap the REGISTER part in another dag to make sure

llvm/test/MC/M68k/Relocations/data-abs.s

 ; RUN: llvm-mc -triple m68k -filetype=obj %s -o - \
 ; RUN:   | llvm-readobj -r - | FileCheck -check-prefix=RELOC %s
 ; RUN: llvm-mc -triple m68k -show-encoding %s -o - \
 ; RUN:   | FileCheck -check-prefix=INSTR -check-prefix=FIXUP %s
 
 ; RELOC: R_68K_32 dst 0x0
 ; INSTR: move.l dst, %d0
 ; FIXUP: fixup A - offset: 2, value: dst, kind: FK_Data_4
 move.l  dst, %d0
+
+; Relocating immediate values
+
+; RELOC: R_68K_8 str8 0x0
+; INSTR: move.b  #str8,  (4,%sp)
+; FIXUP: fixup A - offset: 3, value: str8, kind: FK_Data_1
+move.b  #str8,  (4,%sp)
+
+; RELOC: R_68K_16 str16 0x0
+; INSTR: move.w  #str16,  (4,%sp)
+; FIXUP: fixup A - offset: 2, value: str16, kind: FK_Data_2
+move.w  #str16, (4,%sp)
+
+; RELOC: R_68K_32 str32 0x0
+; INSTR: move.l  #str32,  (4,%sp)
+; FIXUP: fixup A - offset: 2, value: str32, kind: FK_Data_4
+move.l  #str32, (4,%sp)