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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Replace &a[x] - c * y with &a[x - y]"
href="https://bugs.llvm.org/show_bug.cgi?id=47431">47431</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Replace &a[x] - c * y with &a[x - y]
</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>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<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.bolvansky@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>typedef __SIZE_TYPE__ size_t;
size_t a[64];
size_t* f(size_t b, size_t c)
{
return &a[b] + 1 * c;
}
size_t* g(size_t b, size_t c)
{
return &a[b + c];
}
size_t* fm(size_t b, size_t c)
{
return &a[b] - 1 * c;
}
size_t* gm(size_t b, size_t c)
{
return &a[b - c];
}
Clang:
f(unsigned long, unsigned long): # @f(unsigned
long, unsigned long)
shl rsi, 3
lea rax, [rsi + 8*rdi]
add rax, offset a
ret
g(unsigned long, unsigned long): # @g(unsigned
long, unsigned long)
add rdi, rsi
lea rax, [8*rdi + a]
ret
fm(unsigned long, unsigned long): # @fm(unsigned
long, unsigned long)
lea rax, [8*rdi + a]
shl rsi, 3
sub rax, rsi
ret
gm(unsigned long, unsigned long): # @gm(unsigned
long, unsigned long)
sub rdi, rsi
lea rax, [8*rdi + a]
ret
GCC:
f(unsigned long, unsigned long):
add rdi, rsi
lea rax, a[0+rdi*8]
ret
g(unsigned long, unsigned long):
add rdi, rsi
lea rax, a[0+rdi*8]
ret
fm(unsigned long, unsigned long):
sub rdi, rsi
lea rax, a[0+rdi*8]
ret
gm(unsigned long, unsigned long):
sub rdi, rsi
lea rax, a[0+rdi*8]
ret
ICC:
f(unsigned long, unsigned long):
add rdi, rsi #5.11
lea rax, QWORD PTR [a+rdi*8] #5.11
ret #5.11
g(unsigned long, unsigned long):
add rdi, rsi #10.17
lea rax, QWORD PTR [a+rdi*8] #10.11
ret
Godbolt:
<a href="https://godbolt.org/z/6W3rKd">https://godbolt.org/z/6W3rKd</a></pre>
</div>
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