<html>
<head>
<base href="https://bugs.llvm.org/">
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - multiply lowering of divide-by-constant doesn't occur on haswell"
href="https://bugs.llvm.org/show_bug.cgi?id=38649">38649</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>multiply lowering of divide-by-constant doesn't occur on haswell
</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>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>jorg.brown@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Source:
struct SecsAndTicks {
uint64_t seconds;
uint32_t ticks;
};
SecsAndTicks DivBy4Bill(uint64_t tix) {
return {tix / 4000000000,
uint32_t(tix % 4000000000)};
}
x86-64 codegen:
movq %rdi, %rax
shrq $11, %rax
movabsq $4835703278458517, %rcx # imm = 0x112E0BE826D695
mulq %rcx
shrq $9, %rdx
imull $-294967296, %edx, %eax # imm = 0xEE6B2800
subl %eax, %edi
movq %rdx, %rax
movl %edi, %edx
retq
march=haswell codegen:
movl $4000000000, %ecx # imm = 0xEE6B2800
movq %rdi, %rax
shrq $32, %rax
je .LBB0_1
xorl %edx, %edx
movq %rdi, %rax
divq %rcx
retq
.LBB0_1:
xorl %edx, %edx
movl %edi, %eax
divl %ecx
retq
See <a href="https://godbolt.org/g/qGTDGN">https://godbolt.org/g/qGTDGN</a> for repro</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>