[AVR] Fix rotate instructions

This patch fixes some issues with the RORB pseudo instruction.

  - A minor issue in which the instructions were said to use the SREG,
    which is not true.
  - An issue with the BLD instruction, which did not have an output operand.
  - A major issue in which invalid instructions were generated. The fix
    also reduce RORB from 4 to 3 instructions, so it's also a small
    optimization.

These issues were flagged by the machine verifier.

Differential Revision: https://reviews.llvm.org/D96957

lib/Target/AVR/AVRExpandPseudoInsts.cpp

@@ -1345,42 +1345,20 @@ bool AVRExpandPseudo::expand<AVR::RORBRd>(Block &MBB, BlockIt MBBI) {
   // to explicitly add the carry bit.
 
   MachineInstr &MI = *MBBI;
-  unsigned OpShiftOut, OpLoad, OpShiftIn, OpAdd;
   Register DstReg = MI.getOperand(0).getReg();
-  bool DstIsDead = MI.getOperand(0).isDead();
-  OpShiftOut = AVR::LSRRd;
-  OpLoad = AVR::LDIRdK;
-  OpShiftIn = AVR::RORRd;
-  OpAdd = AVR::ORRdRr;
 
-  // lsr r16
+  // bst r16, 0
-  // ldi r0, 0
+  // ror r16
-  // ror r0
+  // bld r16, 7
-  // or r16, r17
 
-  // Shift out
+  // Move the lowest bit from DstReg into the T bit
-  buildMI(MBB, MBBI, OpShiftOut)
+  buildMI(MBB, MBBI, AVR::BST).addReg(DstReg).addImm(0);
-    .addReg(DstReg, RegState::Define | getDeadRegState(DstIsDead))
-    .addReg(DstReg);
 
-  // Put 0 in temporary register
+  // Rotate to the right
-  buildMI(MBB, MBBI, OpLoad)
+  buildMI(MBB, MBBI, AVR::RORRd, DstReg).addReg(DstReg);
-    .addReg(SCRATCH_REGISTER, RegState::Define | getDeadRegState(true))
-    .addImm(0x00);
 
-  // Shift in
+  // Move the T bit into the highest bit of DstReg.
-  buildMI(MBB, MBBI, OpShiftIn)
+  buildMI(MBB, MBBI, AVR::BLD, DstReg).addReg(DstReg).addImm(7);
-    .addReg(SCRATCH_REGISTER, RegState::Define | getDeadRegState(true))
-    .addReg(SCRATCH_REGISTER);
-
-  // Add the results together using an or-instruction
-  auto MIB = buildMI(MBB, MBBI, OpAdd)
-    .addReg(DstReg, RegState::Define | getDeadRegState(DstIsDead))
-    .addReg(DstReg)
-    .addReg(SCRATCH_REGISTER);
-
-  // SREG is always implicitly killed
-  MIB->getOperand(2).setIsKill();
 
   MI.eraseFromParent();
   return true;

lib/Target/AVR/AVRInstrInfo.td

@@ -1735,20 +1735,19 @@ Defs = [SREG] in
                       "asrw\t$rd",
                       [(set i16:$rd, (AVRasr i16:$src)), (implicit SREG)]>;
 
+  def ROLBRd : Pseudo<(outs GPR8:$rd),
+                      (ins GPR8:$src),
+                      "rolb\t$rd",
+                      [(set i8:$rd, (AVRrol i8:$src)), (implicit SREG)]>;
+
+  def RORBRd : Pseudo<(outs GPR8:$rd),
+                      (ins GPR8:$src),
+                      "rorb\t$rd",
+                      [(set i8:$rd, (AVRror i8:$src)), (implicit SREG)]>;
+
   // Bit rotate operations.
   let Uses = [SREG] in
   {
-    // 8-bit ROL is an alias of ADC Rd, Rd
-
-    def ROLBRd : Pseudo<(outs GPR8:$rd),
-                        (ins GPR8:$src),
-                        "rolb\t$rd",
-                        [(set i8:$rd, (AVRrol i8:$src)), (implicit SREG)]>;
-
-    def RORBRd : Pseudo<(outs GPR8:$rd),
-                        (ins GPR8:$src),
-                        "rorb\t$rd",
-                        [(set i8:$rd, (AVRror i8:$src)), (implicit SREG)]>;
 
     def ROLWRd : Pseudo<(outs DREGS:$rd),
                         (ins DREGS:$src),
@@ -1804,10 +1803,11 @@ def BST : FRdB<0b01,
                "bst\t$rd, $b",
                []>;
 
-let Uses = [SREG] in
+let Constraints = "$src = $rd",
+Uses = [SREG] in
 def BLD : FRdB<0b00,
-               (outs),
+               (outs GPR8:$rd),
-               (ins GPR8:$rd, i8imm:$b),
+               (ins GPR8:$src, i8imm:$b),
                "bld\t$rd, $b",
                []>;
 

test/CodeGen/AVR/rot.ll

@@ -37,10 +37,9 @@ define i8 @ror8(i8 %val, i8 %amt) {
   ; CHECK-NEXT: brmi .LBB1_2
 
 ; CHECK-NEXT: .LBB1_1:
-  ; CHECK-NEXT: lsr r24
+  ; CHECK-NEXT: bst r24, 0
-  ; CHECK-NEXT: ldi r0, 0
+  ; CHECK-NEXT: ror r24
-  ; CHECK-NEXT: ror r0
+  ; CHECK-NEXT: bld r24, 7
-  ; CHECK-NEXT: or r24, r0
   ; CHECK-NEXT: dec r22
   ; CHECK-NEXT: brpl .LBB1_1