VPExpandSCEVRecipes must be placed in the entry and are alway uniform.
This fixes a crash by always identifying them as uniform, even if the
main vector loop region has been removed.
Fixes https://github.com/llvm/llvm-project/issues/121897.
Update optimizeForVFAndUF to completely remove the vector loop region
when possible. At the moment, we cannot remove the region if it contains
* widened IVs: the recipe is needed to generate the step vector
* reductions: ComputeReductionResults requires the reduction phi recipe
for codegen.
Both cases can be addressed by more explicit modeling.
The patch also includes a number of updates to allow executing VPlans
without a vector loop region.
Depends on https://github.com/llvm/llvm-project/pull/110004
Add missing test coverage of loops where the vector loop region can be
removed that include replicate recipes as well as nested loops.
Extra test coverage for https://github.com/llvm/llvm-project/pull/108378.
Just comparing constant trip counts causes LV to miss cases where the
vector loop body only executes once.
The motivation for this is to remove the need for unrolling to remove
vector loop back-edges, if the body only executes once in more cases.
Reviewed By: Ayal
Differential Revision: https://reviews.llvm.org/D133017
