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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [AArch64] machine combiner converts independent fadds into dependent fadds"
href="https://bugs.llvm.org/show_bug.cgi?id=37789">37789</a>
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<th>Summary</th>
<td>[AArch64] machine combiner converts independent fadds into dependent fadds
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: AArch64
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>spatel+llvm@rotateright.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Copied from:
test/CodeGen/AArch64/fadd-combines.ll
; DAGCombiner transforms this into: (x + 59.0) + (x + 17.0).
; The machine combiner transforms this into a chain of 3 dependent adds:
; ((x + 59.0) + 17.0) + x
define float @fadd_const_multiuse_attr(float %x) #0 {
; CHECK-LABEL: fadd_const_multiuse_attr:
; CHECK: // %bb.0:
; CHECK-NEXT: adrp x9, .LCPI8_1
; CHECK-NEXT: adrp x8, .LCPI8_0
; CHECK-NEXT: ldr s1, [x9, :lo12:.LCPI8_1]
; CHECK-NEXT: ldr s2, [x8, :lo12:.LCPI8_0]
; CHECK-NEXT: fadd s1, s0, s1
; CHECK-NEXT: fadd s1, s2, s1
; CHECK-NEXT: fadd s0, s0, s1
; CHECK-NEXT: ret
%a1 = fadd float %x, 42.0
%a2 = fadd float %a1, 17.0
%a3 = fadd float %a1, %a2
ret float %a3
}
---------------------------------------------------------------------------
That's with no CPU model specified. When I tried setting that to various
existing models, the transform doesn't happen.
I don't see why we would do this transform under any circumstances, but I might
be missing some AArch subtlety.</pre>
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