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[x86] Fix yet another bug in the new vector shuffle lowering's handling

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of widening masks.

We can't widen a zeroing mask unless both elements that would be merged
are either zeroed or undef. This is the only way to widen a mask if it
has a zeroed element.

Also clean up the code here by ordering the checks in a more logical way
and by using the symoblic values for undef and zero. I'm actually torn
on using the symbolic values because the existing code is littered with
the assumption that -1 is undef, and moreover that entries '< 0' are the
special entries. While that works with the values given to these
constants, using the symbolic constants actually makes it a bit more
opaque why this is the case.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218575 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chandler Carruth
2014-09-28 03:30:25 +00:00
parent e05d3b921f
commit 21b69296fb
2 changed files with 53 additions and 7 deletions
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23
lib/Target/X86/X86ISelLowering.cpp
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@@ -9875,27 +9875,36 @@ static SDValue lower256BitVectorShuffle(SDValue Op, SDValue V1, SDValue V2,
static bool canWidenShuffleElements(ArrayRef<int> Mask,
SmallVectorImpl<int> &WidenedMask) {
for (int i = 0, Size = Mask.size(); i < Size; i += 2) {
// Check for any of the sentinel values (negative) and if they are the same,
// we can widen to that.
if (Mask[i] < 0 && Mask[i] == Mask[i + 1]) {
WidenedMask.push_back(Mask[i]);
// If both elements are undef, its trivial.
if (Mask[i] == SM_SentinelUndef && Mask[i + 1] == SM_SentinelUndef) {
WidenedMask.push_back(SM_SentinelUndef);
continue;
}
// Check for an undef mask and a mask value properly aligned to fit with
// a pair of values. If we find such a case, use the non-undef mask's value.
if (Mask[i] == -1 && Mask[i + 1] >= 0 && Mask[i + 1] % 2 == 1) {
if (Mask[i] == SM_SentinelUndef && Mask[i + 1] >= 0 && Mask[i + 1] % 2 == 1) {
WidenedMask.push_back(Mask[i + 1] / 2);
continue;
}
if (Mask[i + 1] == -1 && Mask[i] >= 0 && Mask[i] % 2 == 0) {
if (Mask[i + 1] == SM_SentinelUndef && Mask[i] >= 0 && Mask[i] % 2 == 0) {
WidenedMask.push_back(Mask[i] / 2);
continue;
}
// When zeroing, we need to spread the zeroing across both lanes to widen.
if (Mask[i] == SM_SentinelZero || Mask[i + 1] == SM_SentinelZero) {
if ((Mask[i] == SM_SentinelZero || Mask[i] == SM_SentinelUndef) &&
(Mask[i + 1] == SM_SentinelZero || Mask[i + 1] == SM_SentinelUndef)) {
WidenedMask.push_back(SM_SentinelZero);
continue;
}
return false;
}
// Finally check if the two mask values are adjacent and aligned with
// a pair.
if (Mask[i] != -1 && Mask[i] % 2 == 0 && Mask[i] + 1 == Mask[i + 1]) {
if (Mask[i] != SM_SentinelUndef && Mask[i] % 2 == 0 && Mask[i] + 1 == Mask[i + 1]) {
WidenedMask.push_back(Mask[i] / 2);
continue;
}