[AVR] Remove earlyclobber from LDDRdPtrQ

LDDRdPtrQ was marked as earlyclobber, which doesn't play well with
GreedyRA (which can generate this instruction through
`loadRegFromStackSlot()`).

This seems to be the same case as:

https://github.com/llvm/llvm-project/blob/a99b912c9b74f6ef91786b4dfbc25160c27d3b41/llvm/lib/Target/AVR/AVRInstrInfo.td#L1421

Note that I'm not really sure the approach presented here is correct -
intuitively, this instruction shouldn't rely on earlyclobber, since it
doesn't have any input registers except for the implied `Y`, but maybe
I'm misunderstanding how earlyclobber is supposed to work.

Closes #81911.

Author: Patryk27

llvm/lib/Target/AVR/AVRInstrInfo.td

@@ -1398,7 +1398,7 @@ let mayLoad = 1, hasSideEffects = 0,
 
 // Load indirect with displacement operations.
 let canFoldAsLoad = 1, isReMaterializable = 1 in {
-  let Constraints = "@earlyclobber $reg" in def LDDRdPtrQ
+  def LDDRdPtrQ
       : FSTDLDD<0,
                 (outs GPR8
                  : $reg),

llvm/test/CodeGen/AVR/bug-81911.ll

@@ -0,0 +1,163 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
+; RUN: llc < %s -mtriple=avr -mcpu=atmega328 -O1 -verify-machineinstrs | FileCheck %s
+
+define internal i8 @main() {
+; CHECK-LABEL: main:
+; CHECK:       ; %bb.0: ; %bb0
+; CHECK-NEXT:    push r2
+; CHECK-NEXT:    push r3
+; CHECK-NEXT:    push r4
+; CHECK-NEXT:    push r5
+; CHECK-NEXT:    push r6
+; CHECK-NEXT:    push r7
+; CHECK-NEXT:    push r8
+; CHECK-NEXT:    push r9
+; CHECK-NEXT:    push r10
+; CHECK-NEXT:    push r11
+; CHECK-NEXT:    push r12
+; CHECK-NEXT:    push r13
+; CHECK-NEXT:    push r14
+; CHECK-NEXT:    push r15
+; CHECK-NEXT:    push r16
+; CHECK-NEXT:    push r17
+; CHECK-NEXT:    push r28
+; CHECK-NEXT:    push r29
+; CHECK-NEXT:    in r28, 61
+; CHECK-NEXT:    in r29, 62
+; CHECK-NEXT:    sbiw r28, 13
+; CHECK-NEXT:    in r0, 63
+; CHECK-NEXT:    cli
+; CHECK-NEXT:    out 62, r29
+; CHECK-NEXT:    out 63, r0
+; CHECK-NEXT:    out 61, r28
+; CHECK-NEXT:    ldi r16, 0
+; CHECK-NEXT:    ldi r17, 0
+; CHECK-NEXT:    ldi r18, -1
+; CHECK-NEXT:    ;APP
+; CHECK-NEXT:    ldi r24, 123
+; CHECK-NEXT:    ;NO_APP
+; CHECK-NEXT:    std Y+1, r24 ; 1-byte Folded Spill
+; CHECK-NEXT:    movw r24, r28
+; CHECK-NEXT:    adiw r24, 6
+; CHECK-NEXT:    std Y+3, r25 ; 2-byte Folded Spill
+; CHECK-NEXT:    std Y+2, r24 ; 2-byte Folded Spill
+; CHECK-NEXT:    movw r8, r16
+; CHECK-NEXT:    movw r6, r16
+; CHECK-NEXT:    movw r4, r16
+; CHECK-NEXT:    movw r2, r16
+; CHECK-NEXT:    rjmp .LBB0_2
+; CHECK-NEXT:  .LBB0_1: ; %bb1
+; CHECK-NEXT:    ; in Loop: Header=BB0_2 Depth=1
+; CHECK-NEXT:    andi r30, 1
+; CHECK-NEXT:    ldd r31, Y+4 ; 1-byte Folded Reload
+; CHECK-NEXT:    dec r31
+; CHECK-NEXT:    cpi r30, 0
+; CHECK-NEXT:    movw r8, r18
+; CHECK-NEXT:    movw r6, r20
+; CHECK-NEXT:    movw r4, r22
+; CHECK-NEXT:    movw r2, r24
+; CHECK-NEXT:    mov r18, r31
+; CHECK-NEXT:    brne .LBB0_2
+; CHECK-NEXT:    rjmp .LBB0_4
+; CHECK-NEXT:  .LBB0_2: ; %bb1
+; CHECK-NEXT:    ; =>This Inner Loop Header: Depth=1
+; CHECK-NEXT:    std Y+4, r18 ; 1-byte Folded Spill
+; CHECK-NEXT:    movw r18, r8
+; CHECK-NEXT:    movw r20, r6
+; CHECK-NEXT:    movw r22, r4
+; CHECK-NEXT:    movw r24, r2
+; CHECK-NEXT:    ldi r26, 10
+; CHECK-NEXT:    ldi r27, 0
+; CHECK-NEXT:    movw r10, r26
+; CHECK-NEXT:    movw r12, r16
+; CHECK-NEXT:    movw r14, r16
+; CHECK-NEXT:    call __udivdi3
+; CHECK-NEXT:    std Y+13, r25
+; CHECK-NEXT:    std Y+12, r24
+; CHECK-NEXT:    std Y+11, r23
+; CHECK-NEXT:    std Y+10, r22
+; CHECK-NEXT:    std Y+9, r21
+; CHECK-NEXT:    std Y+8, r20
+; CHECK-NEXT:    std Y+7, r19
+; CHECK-NEXT:    std Y+6, r18
+; CHECK-NEXT:    ldd r30, Y+2 ; 2-byte Folded Reload
+; CHECK-NEXT:    ldd r31, Y+3 ; 2-byte Folded Reload
+; CHECK-NEXT:    ;APP
+; CHECK-NEXT:    ;NO_APP
+; CHECK-NEXT:    ldi r30, 1
+; CHECK-NEXT:    cp r8, r1
+; CHECK-NEXT:    cpc r9, r1
+; CHECK-NEXT:    cpc r6, r16
+; CHECK-NEXT:    cpc r7, r17
+; CHECK-NEXT:    cpc r4, r16
+; CHECK-NEXT:    cpc r5, r17
+; CHECK-NEXT:    cpc r2, r16
+; CHECK-NEXT:    cpc r3, r17
+; CHECK-NEXT:    breq .LBB0_3
+; CHECK-NEXT:    rjmp .LBB0_1
+; CHECK-NEXT:  .LBB0_3: ; %bb1
+; CHECK-NEXT:    ; in Loop: Header=BB0_2 Depth=1
+; CHECK-NEXT:    mov r30, r1
+; CHECK-NEXT:    rjmp .LBB0_1
+; CHECK-NEXT:  .LBB0_4: ; %bb3
+; CHECK-NEXT:    ldd r24, Y+1 ; 1-byte Folded Reload
+; CHECK-NEXT:    std Y+5, r24
+; CHECK-NEXT:    movw r24, r28
+; CHECK-NEXT:    adiw r24, 5
+; CHECK-NEXT:    ;APP
+; CHECK-NEXT:    ;NO_APP
+; CHECK-NEXT:    ldd r24, Y+5
+; CHECK-NEXT:    adiw r28, 13
+; CHECK-NEXT:    in r0, 63
+; CHECK-NEXT:    cli
+; CHECK-NEXT:    out 62, r29
+; CHECK-NEXT:    out 63, r0
+; CHECK-NEXT:    out 61, r28
+; CHECK-NEXT:    pop r29
+; CHECK-NEXT:    pop r28
+; CHECK-NEXT:    pop r17
+; CHECK-NEXT:    pop r16
+; CHECK-NEXT:    pop r15
+; CHECK-NEXT:    pop r14
+; CHECK-NEXT:    pop r13
+; CHECK-NEXT:    pop r12
+; CHECK-NEXT:    pop r11
+; CHECK-NEXT:    pop r10
+; CHECK-NEXT:    pop r9
+; CHECK-NEXT:    pop r8
+; CHECK-NEXT:    pop r7
+; CHECK-NEXT:    pop r6
+; CHECK-NEXT:    pop r5
+; CHECK-NEXT:    pop r4
+; CHECK-NEXT:    pop r3
+; CHECK-NEXT:    pop r2
+; CHECK-NEXT:    ret
+bb0:
+  %0 = alloca i64
+  %1 = alloca i8
+  %2 = tail call i8 asm sideeffect "ldi ${0}, 123", "=&r,~{sreg},~{memory}"()
+
+  br label %bb1
+
+bb1:
+  %3 = phi i64 [ %5, %bb1 ], [ 0, %bb0 ]
+  %4 = phi i8 [ %6, %bb1 ], [ 0, %bb0 ]
+  %5 = udiv i64 %3, 10
+  %6 = add i8 %4, 1
+
+  store i64 %5, ptr %0
+  call void asm sideeffect "", "r,~{memory}"(ptr %0)
+
+  %7 = icmp eq i64 %3, 0
+  %8 = icmp eq i8 %6, 0
+
+  br i1 %7, label %bb3, label %bb1
+
+bb3:
+  store i8 %2, ptr %1
+  call void asm sideeffect "", "r,~{memory}"(ptr %1)
+
+  %9 = load i8, ptr %1
+
+  ret i8 %9
+}