[all-commits] [llvm/llvm-project] b0e77d: [RISCV] Lower the shufflevector equivalent of vect...
Craig Topper via All-commits
all-commits at lists.llvm.org
Thu Feb 10 09:39:50 PST 2022
Author: Craig Topper <craig.topper at sifive.com>
Date: 2022-02-10 (Thu, 10 Feb 2022)
[RISCV] Lower the shufflevector equivalent of vector.splice
We can lower a vector splice to a vslidedown and a vslideup.
The majority of the matching code here came from X86's code for matching
PALIGNR and VPALIGND/Q.
The slidedown and slideup lowering don't really require it to be concatenation,
but it happened to be an interesting pattern with existing analysis code I
This helps with cases where the scalar loop optimizer forwarded a load
result from a previous loop iteration. For example, this happens if the
loop uses x[i] and x[i+1] on the same iteration. The scalar optimizer
will forward x[i+1] load from the previous loop to satisfy x[i] on this
loop. When this get vectorized it results in one element of a vector
being forwarded from the previous loop to be concatenated with elements
loaded on this iteration.
Whether that's more efficient than doing a shifted loaded or reloading
the single scalar and using vslide1up is an interesting question.
But that's not something the backend can help with.
Reviewed By: khchen
Differential Revision: https://reviews.llvm.org/D119039
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