[all-commits] [llvm/llvm-project] a9ffc9: [SPIR-V] Add pre-headers to loops. (#75844)

[Nathan Gauër via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: a9ffc92fc4428723e85485102dfe10fbea966e64
      https://github.com/llvm/llvm-project/commit/a9ffc92fc4428723e85485102dfe10fbea966e64
  Author: Nathan Gauër <brioche at google.com>
  Date:   2024-01-08 (Mon, 08 Jan 2024)

  Changed paths:
    M llvm/lib/Target/SPIRV/SPIRVPreLegalizer.cpp
    M llvm/lib/Target/SPIRV/SPIRVTargetMachine.cpp
    M llvm/lib/Target/SPIRV/SPIRVUtils.cpp
    M llvm/lib/Target/SPIRV/SPIRVUtils.h
    A llvm/test/CodeGen/SPIRV/scfg-add-pre-headers.ll

  Log Message:
  -----------
  [SPIR-V] Add pre-headers to loops. (#75844)

This is the first of the 7 steps outlined in #75801. This PR explicitely
calls the SimplifyLoops pass. Directly following this pass should follow
the 6 others required to structurize the IR.

Running this pass could generate empty basic-blocks, which are implicit
fallthrough to the successor BB.
There was a specific condition in the SPIR-V ISel which handled implicit
fallthrough, but it couldn't work on empty basic-blocks. This commits
removes the old logic, and adds this new logic, which checks all
basic-blocks for implicit fallthroughs, including empty ones.

---------

Signed-off-by: Nathan Gauër <brioche at google.com>