Closed
Description
LLVM IR:
target triple = "avr-atmel-none"
define internal fastcc void @loopy() unnamed_addr {
start:
br label %bb7.preheader
bb2.loopexit: ; preds = %bb10
%0 = icmp ult i8 %.iter.sroa.0.020, 20
%1 = zext i1 %0 to i8
%.iter.sroa.0.0 = add i8 %.iter.sroa.0.020, %1
br i1 %0, label %bb7.preheader, label %bb4
bb7.preheader: ; preds = %bb2.loopexit, %start
%iter.sroa.0.0.21 = phi i8 [ 0, %start ], [ %.iter.sroa.0.020, %bb2.loopexit ]
%.iter.sroa.0.020 = phi i8 [ 1, %start ], [ %.iter.sroa.0.0, %bb2.loopexit ]
%2 = add i8 %iter.sroa.0.0.21, 10
br label %bb10
bb4: ; preds = %bb2.loopexit
ret void
bb10: ; preds = %bb10, %bb7.preheader
%iter1.sroa.0.0.19 = phi i8 [ 0, %bb7.preheader ], [ %.iter1.sroa.0.018, %bb10 ]
%.iter1.sroa.0.018 = phi i8 [ 1, %bb7.preheader ], [ %.iter1.sroa.0.0, %bb10 ]
tail call fastcc void @observe(i8 %2, i8 %iter1.sroa.0.0.19)
%3 = icmp ult i8 %.iter1.sroa.0.018, 48
%4 = zext i1 %3 to i8
%.iter1.sroa.0.0 = add i8 %.iter1.sroa.0.018, %4
br i1 %3, label %bb10, label %bb2.loopexit
}
declare void @observe(i8, i8) unnamed_addr #2
Generated assembly with --filetype=asm:
.text
.file "a.ll"
.p2align 1
.type loopy,@function
loopy: ; @loopy
; BB#0: ; %start
push r15
push r16
push r17
ldi r24, 1
ldi r17, 0
LBB0_3: ; %bb7.preheader
; =>This Loop Header: Depth=1
; Child Loop BB0_4 Depth 2
mov r15, r24
subi r17, -10
ldi r16, 1
ldi r22, 0
LBB0_4: ; %bb10
; Parent Loop BB0_3 Depth=1
; => This Inner Loop Header: Depth=2
mov r24, r17
call observe
cpi r16, 48
ldi r24, 1
brsh .+2
rjmp LBB0_5
; BB#6: ; %bb10
; in Loop: Header=BB0_4 Depth=2
ldi r24, 0
LBB0_5: ; %bb10
; in Loop: Header=BB0_4 Depth=2
add r24, r16
cpi r16, 48
mov r22, r16
mov r16, r24
brsh .+2
rjmp LBB0_4
; BB#1: ; %bb2.loopexit
; in Loop: Header=BB0_3 Depth=1
ldi r24, 1
cpi r15, 20
brsh .+2
rjmp LBB0_2
; BB#7: ; %bb2.loopexit
; in Loop: Header=BB0_3 Depth=1
ldi r24, 0
LBB0_2: ; %bb2.loopexit
; in Loop: Header=BB0_3 Depth=1
add r24, r15
cpi r15, 20
mov r17, r15
brsh .+2
rjmp LBB0_3
; BB#8: ; %bb4
pop r17
pop r16
pop r15
ret
.Lfunc_end0:
.size loopy, .Lfunc_end0-loopy
Disassembly of output generated with --filetype=obj:
a.o: file format elf32-avr
Disassembly of section .text:
00000000 <loopy>:
0: ff 92 push r15
2: 0f 93 push r16
4: 1f 93 push r17
6: 81 e0 ldi r24, 0x01 ; 1
8: 10 e0 ldi r17, 0x00 ; 0
0000000a <LBB0_3>:
a: f8 2e mov r15, r24
c: 16 5f subi r17, 0xF6 ; 246
e: 01 e0 ldi r16, 0x01 ; 1
10: 60 e0 ldi r22, 0x00 ; 0
00000012 <LBB0_4>:
12: 81 2f mov r24, r17
14: 0e 94 00 00 call 0 ; 0x0 <loopy>
18: 00 33 cpi r16, 0x30 ; 48
1a: 81 e0 ldi r24, 0x01 ; 1
1c: 08 f4 brcc .+2 ; 0x20 <LBB0_4+0xe>
1e: 00 c0 rjmp .+0 ; 0x20 <LBB0_4+0xe>
20: 80 e0 ldi r24, 0x00 ; 0
00000022 <LBB0_5>:
22: 80 0f add r24, r16
24: 00 33 cpi r16, 0x30 ; 48
26: 60 2f mov r22, r16
28: 08 2f mov r16, r24
2a: 08 f4 brcc .+2 ; 0x2e <LBB0_5+0xc>
2c: 00 c0 rjmp .+0 ; 0x2e <LBB0_5+0xc>
2e: 81 e0 ldi r24, 0x01 ; 1
30: f4 31 cpi r31, 0x14 ; 20
32: 08 f4 brcc .+2 ; 0x36 <LBB0_5+0x14>
34: 00 c0 rjmp .+0 ; 0x36 <LBB0_5+0x14>
36: 80 e0 ldi r24, 0x00 ; 0
00000038 <LBB0_2>:
38: 8f 0d add r24, r15
3a: f4 31 cpi r31, 0x14 ; 20
3c: 1f 2d mov r17, r15
3e: 08 f4 brcc .+2 ; 0x42 <LBB0_2+0xa>
40: 00 c0 rjmp .+0 ; 0x42 <LBB0_2+0xa>
42: 1f 91 pop r17
44: 0f 91 pop r16
46: ff 90 pop r15
48: 08 95 ret
Note that the .o file uses r31 for comparisons (without ever filling that register) while the .s file, correctly, uses r15, e.g. in LBB0_2:
LBB0_2: ; %bb2.loopexit
; in Loop: Header=BB0_3 Depth=1
add r24, r15
cpi r15, 20
00000038 <LBB0_2>:
38: 8f 0d add r24, r15
3a: f4 31 cpi r31, 0x14 ; 20