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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - X86InterleavedAccess introduces misaligned loads"
href="https://bugs.llvm.org/show_bug.cgi?id=45957">45957</a>
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<th>Summary</th>
<td>X86InterleavedAccess introduces misaligned loads
</td>
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<th>Product</th>
<td>libraries
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>All
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
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<th>Keywords</th>
<td>miscompilation
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<th>Severity</th>
<td>normal
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Backend: X86
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>nunoplopes@sapo.pt
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<th>CC</th>
<td>craig.topper@gmail.com, juneyoung.lee@sf.snu.ac.kr, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, regehr@cs.utah.edu, spatel+llvm@rotateright.com
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<pre>See here:
<a href="https://github.com/llvm/llvm-project/blob/master/llvm/lib/Target/X86/X86InterleavedAccess.cpp#L219">https://github.com/llvm/llvm-project/blob/master/llvm/lib/Target/X86/X86InterleavedAccess.cpp#L219</a>
Value *NewBasePtr =
Builder.CreateGEP(VecBaseTy, VecBasePtr, Builder.getInt32(i));
Instruction *NewLoad =
Builder.CreateAlignedLoad(VecBaseTy, NewBasePtr, LI->getAlign());
Newly created loads inherit the original load's alignment. This is not correct,
as the original load may have a larger alignment than the GEP done above.
A concrete failure we see is in:
Transforms/InterleavedAccess/X86/interleavedLoad.ll
define <32 x i8> @interleaved_load_vf32_i8_stride3(* %ptr) {
%wide.vec = load <96 x i8>, * %ptr, align 128
...
}
=>
define <32 x i8> @interleaved_load_vf32_i8_stride3(* %ptr) {
%1 = bitcast * %ptr to *
%2 = gep * %1, 16 x i32 0
%3 = load <16 x i8>, * %2, align 128 ; <-- this is not 128-byte aligned
%4 = gep * %1, 16 x i32 1
%5 = load <16 x i8>, * %4, align 128
%6 = gep * %1, 16 x i32 2
%7 = load <16 x i8>, * %6, align 128
...
}
Report:
<a href="https://web.ist.utl.pt/nuno.lopes/alive2/index.php?hash=72296a443c683892&test=Transforms%2FInterleavedAccess%2FX86%2FinterleavedLoad.ll">https://web.ist.utl.pt/nuno.lopes/alive2/index.php?hash=72296a443c683892&test=Transforms%2FInterleavedAccess%2FX86%2FinterleavedLoad.ll</a></pre>
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