MIPS: Emulate the new MIPS R6 B{L,G}T{Z,}{AL,}C instructions

MIPS R6 added the following four instructions which share the
BGTZ and BGTZL opcode:

BLTZALC: Compact branch-and-link if GPR rt is < to zero
BGTZALC: Compact branch-and-link if GPR rt is > to zero
BLTZL  : Compact branch if GPR rt is < to zero
BGTZL  : Compact branch if GPR rt is > to zero
BLTC   : Compact branch if GPR rs is less than GPR rt
BLTUC  : Similar to BLTC but unsigned
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>

arch/mips/kernel/branch.c

@@ -635,6 +635,28 @@ int __compute_return_epc_for_insn(struct pt_regs *regs,
 		if (NO_R6EMU)
 			goto sigill_r6;
 	case bgtz_op:
+		/*
+		 * Compact branches for R6 for the
+		 * bgtz and bgtzl opcodes.
+		 * BGTZ  | rs = 0 | rt != 0  == BGTZALC
+		 * BGTZ  | rs = rt != 0      == BLTZALC
+		 * BGTZ  | rs != 0 | rt != 0 == BLTUC
+		 * BGTZL | rs = 0 | rt != 0  == BGTZC
+		 * BGTZL | rs = rt != 0      == BLTZC
+		 * BGTZL | rs != 0 | rt != 0 == BLTC
+		 *
+		 * *ZALC varint for BGTZ &&& rt != 0
+		 * For real GTZ{,L}, rt is always 0.
+		 */
+		if (cpu_has_mips_r6 && insn.i_format.rt) {
+			if ((insn.i_format.opcode == blez_op) &&
+			    ((!insn.i_format.rs && insn.i_format.rt) ||
+			    (insn.i_format.rs == insn.i_format.rt)))
+				regs->regs[31] = epc + 4;
+			regs->cp0_epc += 8;
+			break;
+		}
+
 		/* rt field assumed to be zero */
 		if ((long)regs->regs[insn.i_format.rs] > 0) {
 			epc = epc + 4 + (insn.i_format.simmediate << 2);

arch/mips/math-emu/cp1emu.c

@@ -589,6 +589,31 @@ static int isBranchInstr(struct pt_regs *regs, struct mm_decoded_insn dec_insn,
 		if (NO_R6EMU)
 			break;
 	case bgtz_op:
+		/*
+		 * Compact branches for R6 for the
+		 * bgtz and bgtzl opcodes.
+		 * BGTZ  | rs = 0 | rt != 0  == BGTZALC
+		 * BGTZ  | rs = rt != 0      == BLTZALC
+		 * BGTZ  | rs != 0 | rt != 0 == BLTUC
+		 * BGTZL | rs = 0 | rt != 0  == BGTZC
+		 * BGTZL | rs = rt != 0      == BLTZC
+		 * BGTZL | rs != 0 | rt != 0 == BLTC
+		 *
+		 * *ZALC varint for BGTZ &&& rt != 0
+		 * For real GTZ{,L}, rt is always 0.
+		 */
+		if (cpu_has_mips_r6 && insn.i_format.rt) {
+			if ((insn.i_format.opcode == blez_op) &&
+			    ((!insn.i_format.rs && insn.i_format.rt) ||
+			     (insn.i_format.rs == insn.i_format.rt)))
+				regs->regs[31] = regs->cp0_epc +
+					dec_insn.pc_inc;
+			*contpc = regs->cp0_epc + dec_insn.pc_inc +
+				dec_insn.next_pc_inc;
+
+			return 1;
+		}
+
 		if ((long)regs->regs[insn.i_format.rs] > 0)
 			*contpc = regs->cp0_epc +
 				dec_insn.pc_inc +