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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Arm regression for three way min/max"
href="https://bugs.llvm.org/show_bug.cgi?id=35875">35875</a>
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<tr>
<th>Summary</th>
<td>Arm regression for three way min/max
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>david.green@arm.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=19647" name="attach_19647" title="Reproducer">attachment 19647</a> <a href="attachment.cgi?id=19647&action=edit" title="Reproducer">[details]</a></span>
Reproducer
This is <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - Regression for three way min/max"
href="show_bug.cgi?id=35717">https://bugs.llvm.org/show_bug.cgi?id=35717</a>, part 2.
The regression is fixed for x86, we just need to do the same for Arm.
This is a piece of code that at it's heart does a three way min (also
attached):
target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
target triple = "thumbv8m.base-arm-none-eabi"
define void @test(i8* nocapture readonly, i8* nocapture) {
%3 = getelementptr inbounds i8, i8* %0, i32 1
%4 = load i8, i8* %0, align 1
%5 = getelementptr inbounds i8, i8* %0, i32 2
%6 = load i8, i8* %3, align 1
%7 = load i8, i8* %5, align 1
%8 = xor i8 %4, -1
%9 = xor i8 %6, -1
%10 = xor i8 %7, -1
%11 = zext i8 %8 to i32
%12 = zext i8 %9 to i32
%13 = icmp ult i8 %6, %4
%14 = zext i8 %10 to i32
%15 = icmp ult i32 %11, %14
%16 = select i1 %15, i32 %11, i32 %14
%17 = icmp ult i32 %12, %14
%18 = select i1 %17, i32 %12, i32 %14
%19 = select i1 %13, i32 %16, i32 %18
%20 = trunc i32 %19 to i8
%21 = sub nsw i32 %11, %19
%22 = trunc i32 %21 to i8
%23 = sub nsw i32 %12, %19
%24 = trunc i32 %23 to i8
%25 = sub nsw i32 %14, %19
%26 = trunc i32 %25 to i8
%27 = getelementptr inbounds i8, i8* %1, i32 1
store i8 %20, i8* %1, align 1
%28 = getelementptr inbounds i8, i8* %1, i32 2
store i8 %22, i8* %27, align 1
%29 = getelementptr inbounds i8, i8* %1, i32 3
store i8 %24, i8* %28, align 1
store i8 %26, i8* %29, align 1
ret void
}
Because i8 isn't a legal type we don't remove the zext/trunc's. And because the
negated values are also stored we do not fold the 3 selects into 2.</pre>
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