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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Optimizer does wrong load elimination after a branch"
href="https://bugs.llvm.org/show_bug.cgi?id=49939">49939</a>
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<th>Summary</th>
<td>Optimizer does wrong load elimination after a branch
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>11.0
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</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>
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<th>Component</th>
<td>LLVM Codegen
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>mdzar5@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
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<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=24746" name="attach_24746" title="Wrong displacement in "mov" instruction highlighted">attachment 24746</a> <a href="attachment.cgi?id=24746&action=edit" title="Wrong displacement in "mov" instruction highlighted">[details]</a></span>
Wrong displacement in "mov" instruction highlighted
I don't know what exactly goes wrong here. Looks like LLVM 11.0.0 optimizer
generates wrong IR, if Clang is asked to compile this program:
clang -v -std=c99 -masm=intel -O3 -finline-hint-functions -S bug.c
// bug.c
#include <stdint.h>
typedef unsigned char byte;
typedef uint32_t udword;
typedef struct {
udword x, y, z;
} A;
udword foo(A *s, udword n) {
return s->x + n;
}
void bar(byte *ptr, A *s) {
if (s->y == s->z)
*(ptr + 1) = foo(s, s->z * 3); // -O3 calculates s->y * 3 instead
*ptr = foo(s, s->y);
}</pre>
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