https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77353
Bug ID: 77353
Summary: [AVR] uint16_t instead uint8_t comparison
Product: gcc
Version: 6.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: bseifert at gmx dot at
Target Milestone: ---
Consider the following code:
if (PINA < static_cast<uint8_t>(32))
{
PORTB = 0;
}
It compiles to - as expected:
6dc: 80 b1 in r24, 0x00 ; 0
6de: 80 32 cpi r24, 0x20 ; 32
6e0: 08 f4 brcc .+2 ; 0x6e4 <main+0x8>
6e2: 15 b8 out 0x05, r1 ; 5
In GCC 6.2.0 a uint16_t instead of sufficient uint8_t comparison is performed -
high byte set to 0:
6d8: 80 b1 in r24, 0x00 ; 0
6da: 90 e0 ldi r25, 0x00 ; 0
6dc: 80 97 sbiw r24, 0x20 ; 32
6de: 0c f4 brge .+2 ; 0x6e2 <main+0xa>
6e0: 15 b8 out 0x05, r1 ; 5
Once I also got the following compilation in GCC 6.2.0 with similar code
snippet:
0: 28 2f mov r18, r24
2: 30 e0 ldi r19, 0x00 ; 0
4: 20 32 cpi r18, 0x20 ; 32
6: 31 05 cpc r19, r1
8: 04 f0 brlt .+0 ; 0xa <ADC::measure(unsigned
char)+0xa>
Here also a uint16_t instead of uint8_t comparison is performed and the even
less performant cpi/cpc instructions are used instead of sbiw.
