[mips][microMIPS] Fix issue with offset operand of BALC and BC instructions

[zoran.jovanovic]

Summary

Value of offset operand for microMIPS BALC and BC instructions is currently shifted 2 bits, but it should be 1 bit.

[dsanders]

LGTM with a couple nits

lib/Target/Mips/Disassembler/MipsDisassembler.cpp

1869

They're functionally the same thing but I'd slightly prefer '<< 1' over '* 2' since we're talking about shifting bits rather than arithmetic.

lib/Target/Mips/MCTargetDesc/MipsMCCodeEmitter.cpp

356–359

Please format as clang-format would.

lib/Target/Mips/Disassembler/MipsDisassembler.cpp

 
 // DecodeBranchTargetMM - Decode microMIPS branch offset, which is
 // shifted left by 1 bit.
 static DecodeStatus DecodeBranchTargetMM(MCInst &Inst,
                                          unsigned Offset,
                                          uint64_t Address,
                                          const void *Decoder);
 
+// DecodeBranchTarget26MM - Decode microMIPS branch offset, which is
+// shifted left by 1 bit.
+static DecodeStatus DecodeBranchTarget26MM(MCInst &Inst,
+                                           unsigned Offset,
+                                           uint64_t Address,
+                                           const void *Decoder);
+
 // DecodeJumpTargetMM - Decode microMIPS jump target, which is
 // shifted left by 1 bit.
 static DecodeStatus DecodeJumpTargetMM(MCInst &Inst,
                                        unsigned Insn,
                                        uint64_t Address,
                                        const void *Decoder);
 
 static DecodeStatus DecodeMem(MCInst &Inst,
static DecodeStatus DecodeBranchTargetMM(MCInst &Inst,
                                          unsigned Offset,
                                          uint64_t Address,
                                          const void *Decoder) {
   int32_t BranchOffset = SignExtend32<16>(Offset) * 2;
   Inst.addOperand(MCOperand::createImm(BranchOffset));
   return MCDisassembler::Success;
 }
 
+static DecodeStatus DecodeBranchTarget26MM(MCInst &Inst,
+  unsigned Offset,
+  uint64_t Address,
+  const void *Decoder) {
+  int32_t BranchOffset = SignExtend32<26>(Offset) * 2;
+
+  Inst.addOperand(MCOperand::createImm(BranchOffset));
+  return MCDisassembler::Success;
+}
+
 static DecodeStatus DecodeJumpTargetMM(MCInst &Inst,
                                        unsigned Insn,
                                        uint64_t Address,
                                        const void *Decoder) {
   unsigned JumpOffset = fieldFromInstruction(Insn, 0, 26) << 1;
   Inst.addOperand(MCOperand::createImm(JumpOffset));
   return MCDisassembler::Success;
 }

lib/Target/Mips/MCTargetDesc/MipsMCCodeEmitter.h

public:
 
   // getBranchTarget26OpValue - Return binary encoding of the branch
   // offset operand. If the machine operand requires relocation,
   // record the relocation and return zero.
   unsigned getBranchTarget26OpValue(const MCInst &MI, unsigned OpNo,
                                     SmallVectorImpl<MCFixup> &Fixups,
                                     const MCSubtargetInfo &STI) const;
 
+  // getBranchTarget26OpValueMM - Return binary encoding of the branch
+  // offset operand. If the machine operand requires relocation,
+  // record the relocation and return zero.
+  unsigned getBranchTarget26OpValueMM(const MCInst &MI, unsigned OpNo,
+                                      SmallVectorImpl<MCFixup> &Fixups,
+                                      const MCSubtargetInfo &STI) const;
+
   // getJumpOffset16OpValue - Return binary encoding of the jump
   // offset operand. If the machine operand requires relocation,
   // record the relocation and return zero.
   unsigned getJumpOffset16OpValue(const MCInst &MI, unsigned OpNo,
                                   SmallVectorImpl<MCFixup> &Fixups,
                                   const MCSubtargetInfo &STI) const;
 
   // getMachineOpValue - Return binary encoding of operand. If the machin

lib/Target/Mips/MCTargetDesc/MipsMCCodeEmitter.cpp

getBranchTarget26OpValue(const MCInst &MI, unsigned OpNo,
 
   const MCExpr *FixupExpression = MCBinaryExpr::createAdd(
       MO.getExpr(), MCConstantExpr::create(-4, Ctx), Ctx);
   Fixups.push_back(MCFixup::create(0, FixupExpression,
                                    MCFixupKind(Mips::fixup_MIPS_PC26_S2)));
   return 0;
 }
 
+/// getBranchTarget26OpValueMM - Return binary encoding of the branch
+/// target operand. If the machine operand requires relocation,
+/// record the relocation and return zero.
+unsigned MipsMCCodeEmitter::
+getBranchTarget26OpValueMM(const MCInst &MI, unsigned OpNo,
+SmallVectorImpl<MCFixup> &Fixups,
+const MCSubtargetInfo &STI) const {
+
+  const MCOperand &MO = MI.getOperand(OpNo);
+
+  // If the destination is an immediate, divide by 2.
+  if (MO.isImm()) return MO.getImm() >> 1;
+
+  // TODO: Push 26 PC fixup.
+  return 0;
+}
+
 /// getJumpOffset16OpValue - Return binary encoding of the jump
 /// target operand. If the machine operand requires relocation,
 /// record the relocation and return zero.
 unsigned MipsMCCodeEmitter::
 getJumpOffset16OpValue(const MCInst &MI, unsigned OpNo,
                        SmallVectorImpl<MCFixup> &Fixups,
                        const MCSubtargetInfo &STI) const {
 

lib/Target/Mips/MicroMips32r6InstrInfo.td

 //=- MicroMips32r6InstrInfo.td - MicroMips r6 Instruction Information -*- tablegen -*-=//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
 // This file describes microMIPSr6 instructions.
 //
 //===----------------------------------------------------------------------===//
 
+def brtarget26_mm : Operand<OtherVT> {
+  let EncoderMethod = "getBranchTarget26OpValueMM";
+  let OperandType = "OPERAND_PCREL";
+  let DecoderMethod = "DecodeBranchTarget26MM";
+  let ParserMatchClass = MipsJumpTargetAsmOperand;
+}
+
 //===----------------------------------------------------------------------===//
 //
 // Instruction Encodings
 //
 //===----------------------------------------------------------------------===//
 class ADD_MMR6_ENC : ARITH_FM_MMR6<"add", 0x110>;
 class ADDIU_MMR6_ENC : ADDI_FM_MMR6<"addiu", 0xc>;
 class ADDU_MMR6_ENC : ARITH_FM_MMR6<"addu", 0x150>;

 class BC_MMR6_DESC_BASE<string instr_asm, DAGOperand opnd>
     : BRANCH_DESC_BASE, MMR6Arch<instr_asm> {
   dag InOperandList = (ins opnd:$offset);
   dag OutOperandList = (outs);
   string AsmString = !strconcat(instr_asm, "\t$offset");
   bit isBarrier = 1;
 }
 
-class BALC_MMR6_DESC : BC_MMR6_DESC_BASE<"balc", brtarget26> {
+class BALC_MMR6_DESC : BC_MMR6_DESC_BASE<"balc", brtarget26_mm> {
   bit isCall = 1;
   list<Register> Defs = [RA];
 }
-class BC_MMR6_DESC : BC_MMR6_DESC_BASE<"bc", brtarget26>;
+class BC_MMR6_DESC : BC_MMR6_DESC_BASE<"bc", brtarget26_mm>;
 
 class BC16_MMR6_DESC : MicroMipsInst16<(outs), (ins brtarget10_mm:$offset),
                                        !strconcat("bc16", "\t$offset"), [],
                                        II_BC, FrmI>,
                        MMR6Arch<"bc16">, MicroMipsR6Inst16 {
   let isBranch = 1;
   let isTerminator = 1;
   let isBarrier = 1;

test/MC/Disassembler/Mips/micromips32r6/valid.txt

 0xd0 0x64 0x04 0xd2 # CHECK: andi $3, $4, 1234
 0x10 0x62 0xff 0xe9 # CHECK: aui $3, $2, -23
 0x74 0x40 0x02 0x9a # CHECK: beqzalc $2, 1332
 0x7c 0x40 0x02 0x9a # CHECK: bnezalc $2, 1332
 0xc0 0x42 0x02 0x9a # CHECK: bgezalc $2, 1332
 0xe0 0x40 0x02 0x9a # CHECK: bgtzalc $2, 1332
 0xe0 0x42 0x02 0x9a # CHECK: bltzalc $2, 1332
 0xc0 0x40 0x02 0x9a # CHECK: blezalc $2, 1332
-0xb4 0x37 0x96 0xb8 # CHECK: balc 14572256
-0x94 0x37 0x96 0xb8 # CHECK: bc 14572256
+0xb4 0x37 0x96 0xb8 # CHECK: balc 7286128
+0x94 0x37 0x96 0xb8 # CHECK: bc 7286128
 0x00 0x44 0x0b 0x3c # CHECK: bitswap $4, $2
 0x00 0x00 0x00 0x07 # CHECK: break
 0x00 0x07 0x00 0x07 # CHECK: break 7
 0x00 0x07 0x01 0x47 # CHECK: break 7, 5
 0x20 0x25 0x60 0x08 # CHECK: cache 1, 8($5)
 0x01 0x65 0x4b 0x3c # CHECK: clo $11, $5
 0x03 0x80 0xe8 0x50 # CHECK: clz $sp, $gp
 0x00 0xa4 0x19 0x18 # CHECK: div $3, $4, $5

test/MC/Mips/micromips32r6/valid.s

# RUN: llvm-mc %s -triple=mips-unknown-linux -show-encoding -mcpu=mips32r6 -mattr=micromips | FileCheck %s
   align $4, $2, $3, 2      # CHECK: align $4, $2, $3, 2 # encoding: [0x00,0x43,0x24,0x1f]
   aui $3,$2,-23            # CHECK: aui $3, $2, -23     # encoding: [0x10,0x62,0xff,0xe9]
   beqzalc $2, 1332         # CHECK: beqzalc $2, 1332    # encoding: [0x74,0x40,0x02,0x9a]
   bnezalc $2, 1332         # CHECK: bnezalc $2, 1332    # encoding: [0x7c,0x40,0x02,0x9a]
   bgezalc $2, 1332         # CHECK: bgezalc $2, 1332    # encoding: [0xc0,0x42,0x02,0x9a]
   bgtzalc $2, 1332         # CHECK: bgtzalc $2, 1332    # encoding: [0xe0,0x40,0x02,0x9a]
   bltzalc $2, 1332         # CHECK: bltzalc $2, 1332    # encoding: [0xe0,0x42,0x02,0x9a]
   blezalc $2, 1332         # CHECK: blezalc $2, 1332    # encoding: [0xc0,0x40,0x02,0x9a]
-  balc 14572256            # CHECK: balc 14572256       # encoding: [0xb4,0x37,0x96,0xb8]
+  balc 7286128             # CHECK: balc 7286128        # encoding: [0xb4,0x37,0x96,0xb8]
   b 132                    # CHECK: bc16 132            # encoding: [0xcc,0x42]
-  bc 14572256              # CHECK: bc 14572256         # encoding: [0x94,0x37,0x96,0xb8]
+  bc 7286128               # CHECK: bc 7286128          # encoding: [0x94,0x37,0x96,0xb8]
   bc16 132                 # CHECK: bc16 132            # encoding: [0xcc,0x42]
   beqzc16 $6, 20           # CHECK: beqzc16 $6, 20      # encoding: [0x8f,0x0a]
   bnezc16 $6, 20           # CHECK: bnezc16 $6, 20      # encoding: [0xaf,0x0a]
   bitswap $4, $2           # CHECK: bitswap $4, $2      # encoding: [0x00,0x44,0x0b,0x3c]
   break                    # CHECK: break               # encoding: [0x00,0x00,0x00,0x07]
   break 7                  # CHECK: break 7             # encoding: [0x00,0x07,0x00,0x07]
   break 7, 5               # CHECK: break 7, 5          # encoding: [0x00,0x07,0x01,0x47]
   cache 1, 8($5)           # CHECK: cache 1, 8($5)      # encoding: [0x20,0x25,0x60,0x08]