[all-commits] [llvm/llvm-project] c5cac4: [RISCV] Fix lowering of BUILD_VECTORs as VID seque...

[Fraser Cormack via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: c5cac48549ed254cd5ad5eef770ebfb22ccd9f64
      https://github.com/llvm/llvm-project/commit/c5cac48549ed254cd5ad5eef770ebfb22ccd9f64
  Author: Fraser Cormack <fraser at codeplay.com>
  Date:   2022-04-19 (Tue, 19 Apr 2022)

  Changed paths:
    M llvm/lib/Target/RISCV/RISCVISelLowering.cpp
    M llvm/test/CodeGen/RISCV/rvv/fixed-vectors-int-buildvec.ll

  Log Message:
  -----------
  [RISCV] Fix lowering of BUILD_VECTORs as VID sequences

This patch fixes a bug when lowering BUILD_VECTOR via VID sequences.
After adding support for fractional steps in D106533, elements with zero
steps may be skipped if no step has yet been computed. This allowed
certain sequences to slip through the cracks, being identified as VID
sequences when in fact they are not.

The fix for this is to perform a second loop over the BUILD_VECTOR to
validate the entire sequence once the step has been computed. This isn't
the most efficient, but on balance the code is more readable and
maintainable than doing back-validation during the first loop.

Fixes the tests introduced in D123785.

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D123786