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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Add AVX-512 support in X86TargetLowering::emitFMA3Instr"
href="https://llvm.org/bugs/show_bug.cgi?id=26417">26417</a>
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<tr>
<th>Summary</th>
<td>Add AVX-512 support in X86TargetLowering::emitFMA3Instr
</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>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>hfinkel@anl.gov
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=15788" name="attach_15788" title="Kernel where this might matter">attachment 15788</a> <a href="attachment.cgi?id=15788&action=edit" title="Kernel where this might matter">[details]</a></span>
Kernel where this might matter
In llvm/lib/Target/X86/X86ISelLowering.cpp we have:
// Replace 213-type (isel default) FMA3 instructions with 231-type for
// accumulator loops. Writing back to the accumulator allows the coalescer
// to remove extra copies in the loop.
// FIXME: Do this on AVX512. We don't support 231 variants yet (PR23937).
MachineBasicBlock *
X86TargetLowering::emitFMA3Instr(MachineInstr *MI,
MachineBasicBlock *MBB) const {
...
But PR23937 has now been fixed, and we should add AVX-512 support here.
I've attached a small test case (C with intrinsics) where I suspect this might
matter.
$ clang -S -o - -march=knl -O3 ~/tmp/avx512mm.c
...
.LBB0_3: # %.preheader10
# Parent Loop BB0_1 Depth=1
# Parent Loop BB0_2 Depth=2
# => This Inner Loop Header: Depth=3
vmovaps %zmm1, %zmm8
vmovaps %zmm2, %zmm9
vmovaps %zmm3, %zmm10
vmovaps %zmm4, %zmm11
vmovaps %zmm6, %zmm12
vmovaps %zmm7, %zmm13
vmovaps %zmm0, %zmm14
vmovaps %zmm5, %zmm1
vmovapd (%rdx), %zmm0
vmovaps %zmm0, %zmm5
vfmadd231pd -7168(%r14){1to8}, %zmm1, %zmm5
vmovaps %zmm0, %zmm1
vfmadd231pd -6144(%r14){1to8}, %zmm8, %zmm1
vmovaps %zmm0, %zmm2
vfmadd231pd -5120(%r14){1to8}, %zmm9, %zmm2
vmovaps %zmm0, %zmm3
vfmadd231pd -4096(%r14){1to8}, %zmm10, %zmm3
vmovaps %zmm0, %zmm4
vfmadd231pd -3072(%r14){1to8}, %zmm11, %zmm4
vmovaps %zmm0, %zmm6
vfmadd231pd -2048(%r14){1to8}, %zmm12, %zmm6
vmovaps %zmm0, %zmm7
vfmadd231pd -1024(%r14){1to8}, %zmm13, %zmm7
vfmadd231pd (%r14){1to8}, %zmm14, %zmm0
addq $8, %r14
addq $1024, %rdx # imm = 0x400
decq %r10
jne .LBB0_3
...
and I this should select a different FMA form to avoid the excess moves.</pre>
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