[ARM] Operands for PKHTB alias should be swapped

[olista01]

Summary

When the shift immediate is zero, PKHTB is an alias for PKHBT, but the order of the input operands needs to be swapped.

[rengolin]

LGTM. Thanks!

lib/Target/ARM/ARMInstrInfo.td

 // Load / Store Multiple
 def : MnemonicAlias<"ldmfd", "ldm">;
 def : MnemonicAlias<"ldmia", "ldm">;
 def : MnemonicAlias<"ldmea", "ldmdb">;
 def : MnemonicAlias<"stmfd", "stmdb">;
 def : MnemonicAlias<"stmia", "stm">;
 def : MnemonicAlias<"stmea", "stm">;
 
-// PKHBT/PKHTB with default shift amount. PKHTB is equivalent to PKHBT when the
-// shift amount is zero (i.e., unspecified).
+// PKHBT/PKHTB with default shift amount. PKHTB is equivalent to PKHBT with the
+// input operands swapped when the shift amount is zero (i.e., unspecified).
 def : InstAlias<"pkhbt${p} $Rd, $Rn, $Rm",
                 (PKHBT GPRnopc:$Rd, GPRnopc:$Rn, GPRnopc:$Rm, 0, pred:$p)>,
         Requires<[IsARM, HasV6]>;
 def : InstAlias<"pkhtb${p} $Rd, $Rn, $Rm",
-                (PKHBT GPRnopc:$Rd, GPRnopc:$Rn, GPRnopc:$Rm, 0, pred:$p)>,
+                (PKHBT GPRnopc:$Rd, GPRnopc:$Rm, GPRnopc:$Rn, 0, pred:$p)>,
         Requires<[IsARM, HasV6]>;
 
 // PUSH/POP aliases for STM/LDM
 def : ARMInstAlias<"push${p} $regs", (STMDB_UPD SP, pred:$p, reglist:$regs)>;
 def : ARMInstAlias<"pop${p} $regs", (LDMIA_UPD SP, pred:$p, reglist:$regs)>;
 
 // SSAT/USAT optional shift operand.
 def : ARMInstAlias<"ssat${p} $Rd, $sat_imm, $Rn",

lib/Target/ARM/ARMInstrThumb2.td

 // Alias for MVN with(out) the ".w" optional width specifier.
 def : t2InstAlias<"mvn${s}${p}.w $Rd, $imm",
            (t2MVNi rGPR:$Rd, t2_so_imm:$imm, pred:$p, cc_out:$s)>;
 def : t2InstAlias<"mvn${s}${p} $Rd, $Rm",
            (t2MVNr rGPR:$Rd, rGPR:$Rm, pred:$p, cc_out:$s)>;
 def : t2InstAlias<"mvn${s}${p} $Rd, $ShiftedRm",
            (t2MVNs rGPR:$Rd, t2_so_reg:$ShiftedRm, pred:$p, cc_out:$s)>;
 
-// PKHBT/PKHTB with default shift amount. PKHTB is equivalent to PKHBT when the
-// shift amount is zero (i.e., unspecified).
+// PKHBT/PKHTB with default shift amount. PKHTB is equivalent to PKHBT with the
+// input operands swapped when the shift amount is zero (i.e., unspecified).
 def : InstAlias<"pkhbt${p} $Rd, $Rn, $Rm",
                 (t2PKHBT rGPR:$Rd, rGPR:$Rn, rGPR:$Rm, 0, pred:$p)>,
             Requires<[HasT2ExtractPack, IsThumb2]>;
 def : InstAlias<"pkhtb${p} $Rd, $Rn, $Rm",
-                (t2PKHBT rGPR:$Rd, rGPR:$Rn, rGPR:$Rm, 0, pred:$p)>,
+                (t2PKHBT rGPR:$Rd, rGPR:$Rm, rGPR:$Rn, 0, pred:$p)>,
             Requires<[HasT2ExtractPack, IsThumb2]>;
 
 // PUSH/POP aliases for STM/LDM
 def : t2InstAlias<"push${p}.w $regs", (t2STMDB_UPD SP, pred:$p, reglist:$regs)>;
 def : t2InstAlias<"push${p} $regs", (t2STMDB_UPD SP, pred:$p, reglist:$regs)>;
 def : t2InstAlias<"pop${p}.w $regs", (t2LDMIA_UPD SP, pred:$p, reglist:$regs)>;
 def : t2InstAlias<"pop${p} $regs", (t2LDMIA_UPD SP, pred:$p, reglist:$regs)>;
 

test/MC/ARM/basic-arm-instructions.s

@------------------------------------------------------------------------------
         pkhtb r2, r2, r3, asr #31
         pkhtb r2, r2, r3, asr #15
 
 @ CHECK: pkhbt  r2, r2, r3              @ encoding: [0x13,0x20,0x82,0xe6]
 @ CHECK: pkhbt  r2, r2, r3, lsl #31     @ encoding: [0x93,0x2f,0x82,0xe6]
 @ CHECK: pkhbt  r2, r2, r3              @ encoding: [0x13,0x20,0x82,0xe6]
 @ CHECK: pkhbt  r2, r2, r3, lsl #15     @ encoding: [0x93,0x27,0x82,0xe6]
 
-@ CHECK: pkhbt  r2, r2, r3              @ encoding: [0x13,0x20,0x82,0xe6]
+@ CHECK: pkhbt  r2, r3, r2              @ encoding: [0x12,0x20,0x83,0xe6]
 @ CHECK: pkhtb  r2, r2, r3, asr #31     @ encoding: [0xd3,0x2f,0x82,0xe6]
 @ CHECK: pkhtb  r2, r2, r3, asr #15     @ encoding: [0xd3,0x27,0x82,0xe6]
 
 @------------------------------------------------------------------------------
 @ FIXME: PLD
 @------------------------------------------------------------------------------
 @------------------------------------------------------------------------------
 @ FIXME: PLI

test/MC/ARM/basic-thumb2-instructions.s

@------------------------------------------------------------------------------
         pkhtb r2, r2, r3, asr #31
         pkhtb r2, r2, r3, asr #15
 
 @ CHECK: pkhbt  r2, r2, r3              @ encoding: [0xc2,0xea,0x03,0x02]
 @ CHECK: pkhbt  r2, r2, r3, lsl #31     @ encoding: [0xc2,0xea,0xc3,0x72]
 @ CHECK: pkhbt  r2, r2, r3              @ encoding: [0xc2,0xea,0x03,0x02]
 @ CHECK: pkhbt  r2, r2, r3, lsl #15     @ encoding: [0xc2,0xea,0xc3,0x32]
 
-@ CHECK: pkhbt  r2, r2, r3              @ encoding: [0xc2,0xea,0x03,0x02]
+@ CHECK: pkhbt  r2, r3, r2              @ encoding: [0xc3,0xea,0x02,0x02]
 @ CHECK: pkhtb  r2, r2, r3, asr #31     @ encoding: [0xc2,0xea,0xe3,0x72]
 @ CHECK: pkhtb  r2, r2, r3, asr #15     @ encoding: [0xc2,0xea,0xe3,0x32]
 
 
 @------------------------------------------------------------------------------
 @ PLD(immediate)
 @------------------------------------------------------------------------------
         pld [r5, #-4]