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<base href="https://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Vector constant folding of comparisons does not follow the vector boolean format"
href="https://llvm.org/bugs/show_bug.cgi?id=25763">25763</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Vector constant folding of comparisons does not follow the vector boolean format
</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>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Common Code Generator Code
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>silviu.baranga@arm.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>r253504 introduced constant folding for vector setcc operations:
r253504 | rksimon | 2015-11-18 21:17:19 +0000 (Wed, 18 Nov 2015) | 7 lines
[DAGCombiner] Vector constant folding for comparisons
This patch adds support for vector constant folding of integer/float
comparisons.
This requires FoldConstantVectorArithmetic to support scalar constant operands
(in this case ISD::CONDCASE). In future we should be able to support other
scalar constant types as necessary (and possibly start calling
FoldConstantVectorArithmetic for all node creations)
Differential Revision: <a href="http://reviews.llvm.org/D14683">http://reviews.llvm.org/D14683</a>
This folds vector comparisons by using scalar logic per-lane. However, boolean
output format can differ between scalar and vector operations (it can be either
one or negative one for true). On targets where there is a difference between
the scalar and vector boolean formats, this will cause a miscompile.
Reproducer:
target datalayout = "e-m:e-i64:64-i128:128-n32:64-S128"
target triple = "aarch64--linux-gnu"
declare <8 x i8> @llvm.ctlz.v8i8(<8 x i8>, i1)
define <8 x i16> @dotests_458() {
entry:
%vclz_v.i = call <8 x i8> @llvm.ctlz.v8i8(<8 x i8> <i8 127, i8 38, i8 -1, i8
-128, i8 127, i8 0, i8 0, i8 0>, i1 false) #6
%vsra_n = lshr <8 x i8> %vclz_v.i, <i8 5, i8 5, i8 5, i8 5, i8 5, i8 5, i8 5,
i8 5>
%name_6 = or <8 x i8> %vsra_n, <i8 127, i8 -128, i8 -1, i8 67, i8 84, i8 127,
i8 -1, i8 0>
%cmp.i603 = icmp slt <8 x i8> %name_6, <i8 -57, i8 -128, i8 127, i8 -128, i8
-1, i8 0, i8 -1, i8 -1>
%vmovl.i4.i = sext <8 x i1> %cmp.i603 to <8 x i16>
ret <8 x i16> %vmovl.i4.i
}
Compiled with:
llc -O3 test.ll -o -
Produces:
.text
.file "test.ll"
.section .rodata.cst8,"aM",@progbits,8
.align 3
.LCPI0_0:
.byte 0 // 0x0
.byte 0 // 0x0
.byte 1 // 0x1 ; This should be 0xff!
.byte 0 // 0x0
.byte 0 // 0x0
.byte 0 // 0x0
.byte 0 // 0x0
.byte 0 // 0x0
.text
.globl dotests_458
.align 2
.type dotests_458,@function
dotests_458: // @dotests_458
.cfi_startproc
// BB#0: // %entry
adrp x8, .LCPI0_0
ldr d0, [x8, :lo12:.LCPI0_0]
sshll v0.8h, v0.8b, #0
ret
.Lfunc_end0:
.size dotests_458, .Lfunc_end0-dotests_458
.cfi_endproc</pre>
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