scalarizeBinop currently folds
vec_bo((inselt VecC0, V0, Index), (inselt VecC1, V1, Index))
->
inselt(vec_bo(VecC0, VecC1), scl_bo(V0,V1), Index)
This patch extends this to account for cases where one of the vec_bo operands is already all-constant and performs similar cost checks to determine if the scalar binop with a constant still makes sense:
vec_bo((inselt VecC0, V0, Index), VecC1)
->
inselt(vec_bo(VecC0, VecC1), scl_bo(V0,extractelt(V1,Index)), Index)
Fixes PR42174
Differential Revision: https://reviews.llvm.org/D80885
Goes with proposal in D80885.
This is adapted from the InstCombine tests that were added for
D50992
But these should be adjusted further to provide more interesting
scenarios for x86-specific codegen. Eg, vector types/sizes will
have different costs depending on ISA attributes.
We also need to add tests that include a load of the scalar
variable and add tests that include extra uses of the insert
to further exercise the cost model.
Simon Pilgrim