[RISCV] Infinite loop after D104581

[topperc]

Bugzilla Link	51206
Resolution	FIXED
Resolved on	Oct 11, 2021 20:29
Version	trunk
OS	All
Blocks	#51489
CC	@asb,@nathanchance,@nickdesaulniers
Fixed by commit(s)	54588bc 9ac5717

Extended Description

As reported in D104581 this test causes an infinite loop when compiled with -O2

char aspeed_set_pwm_port_fan_ctrl_priv_0_0,
aspeed_set_pwm_port_fan_ctrl_fan_ctrl;
pwm_store_period, pwm_store_dc_time_on;
pwm_store() {
pwm_store_period = aspeed_set_pwm_port_fan_ctrl_priv_0_0;
pwm_store_period += 1;
pwm_store_dc_time_on =
aspeed_set_pwm_port_fan_ctrl_fan_ctrl * pwm_store_period / 5;
if (pwm_store_dc_time_on)
aspeed_set_pwm_port_duty_rising_falling();
}

The combine from D104581 turns an any_extend into a sign_extend. This gets converted to a zero_extend as the sign bit of input is known to be 0. Then a setcc combine shrinks the setcc inputs back to the pre zero extended value. This allows the zero extend to become an any_extend again. Then the whole process starts over.

[topperc]

Fixed by 54588bc

Also here's the link the ClangBuiltLinux report for this ClangBuiltLinux/linux#1431

[tstellar]

Merged: 9ac5717

[tstellar]

mentioned in issue #51489