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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [X86] any_extend is pessimized by selection"
href="https://bugs.llvm.org/show_bug.cgi?id=42144">42144</a>
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<th>Summary</th>
<td>[X86] any_extend is pessimized by selection
</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>
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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>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>lebedev.ri@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, spatel+llvm@rotateright.com
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</tr></table>
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<div>
<pre>define dso_local zeroext i1 @_Z2t0jj(i32, i32) local_unnamed_addr #0 {
%3 = add i32 %1, -1
%4 = shl i32 1, %3
%5 = and i32 %4, %0
%6 = icmp ne i32 %5, 0
ret i1 %6
}
results in:
# %bb.0:
decb %sil
movzbl %sil, %eax
btl %eax, %edi
setb %al
retq
That movzbl shouldn't be there.
Combining: t0: ch = EntryToken
Optimized legalized selection DAG: %bb.0 '_Z2t0jj:'
SelectionDAG has 16 nodes:
t0: ch = EntryToken
t2: i32,ch = CopyFromReg t0, Register:i32 %0
t4: i32,ch = CopyFromReg t0, Register:i32 %1
t21: i8 = truncate t4
t23: i8 = add t21, Constant:i8<-1>
t27: i32 = any_extend t23
t29: i32 = X86ISD::BT t2, t27
t30: i8 = X86ISD::SETCC Constant:i8<2>, t29
t17: ch,glue = CopyToReg t0, Register:i8 $al, t30
t18: ch = X86ISD::RET_FLAG t17, TargetConstant:i32<0>, Register:i8 $al, t17:1
ISEL: Starting selection on root node: t27: i32 = any_extend t23
ISEL: Starting pattern match
Initial Opcode index to 126894
Match failed at index 126898
Continuing at 127264
TypeSwitch[i32] from 127267 to 127270
Skipped scope entry (due to false predicate) at index 127276, continuing at
127285
Morphed node: t27: i32 = MOVZX32rr8 t23
ISEL: Match complete!
===== Instruction selection ends:
Selected selection DAG: %bb.0 '_Z2t0jj:'
SelectionDAG has 18 nodes:
t0: ch = EntryToken
t2: i32,ch = CopyFromReg t0, Register:i32 %0
t4: i32,ch = CopyFromReg t0, Register:i32 %1
t21: i8 = EXTRACT_SUBREG t4, TargetConstant:i32<1>
t23: i8,i32 = DEC8r t21
t27: i32 = MOVZX32rr8 t23
t29: i32 = BT32rr t2, t27
t33: ch,glue = CopyToReg t0, Register:i32 $eflags, t29
t30: i8 = SETCCr TargetConstant:i8<2>, t33:1
t17: ch,glue = CopyToReg t0, Register:i8 $al, t30
t18: ch = RET TargetConstant:i32<0>, Register:i8 $al, t17, t17:1
I'm not quite sure where to look though</pre>
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