This patch moves the code to set the correct incoming block for the
backedge value to VPlan::execute.
When generating the phi node, the backedge value is temporarily added
using the pre-header as incoming block. The invalid phi node will be
fixed up during VPlan::execute after main VPlan code generation.
At the same time, the backedge value is also moved to the latch.
This change removes the requirement to create the latch block up-front
for VPWidenIntOrFpInductionRecipe::execute, which in turn will enable
modeling the pre-header in VPlan.
As an alternative, the increment could be modeled as separate recipe,
but that would require more work and a bit of redundant code, as we need
to create the step-vector during VPWidenIntOrFpInductionRecipe::execute
anyways, to create the values for different parts.
Reviewed By: Ayal
Differential Revision: https://reviews.llvm.org/D121617
e7bf2ea934