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1ee3b380df
For the 2s failures in the PR, we have a V4SF VEC_PERM_EXPR in
which the first two elements are duplicates of one element and
the other two are don't-care:
v4sf_b = VEC_PERM_EXPR <v4sf_a, v4sf_a, { 1, 1, ?, ? }>;
The heuristic was to extend this with a blend:
v4sf_b = VEC_PERM_EXPR <v4sf_a, v4sf_a, { 1, 1, 2, 3 }>;
but it seems better to extend a partial duplicate to a full duplicate:
v4sf_b = VEC_PERM_EXPR <v4sf_a, v4sf_a, { 1, 1, 1, 1 }>;
Obviously this is still just a heuristic though.
I wondered whether to restrict this to two elements or more
but couldn't find any examples in which it made a difference.
Either way should be fine for the purposes of fixing this PR.
2020-01-28 Richard Sandiford <richard.sandiford@arm.com>
gcc/
PR tree-optimization/92822
* tree-ssa-forwprop.c (simplify_vector_constructor): When filling
out the don't-care elements of a vector whose significant elements
are duplicates, make the don't-care elements duplicates too.
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