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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [RISCV] Infinite loop after D104581"
href="https://bugs.llvm.org/show_bug.cgi?id=51206">51206</a>
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<th>Summary</th>
<td>[RISCV] Infinite loop after D104581
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: RISC-V
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>craig.topper@gmail.com
</td>
</tr>
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<th>CC</th>
<td>asb@lowrisc.org, llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>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.</pre>
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