[WebAssembly] Optimize BUILD_VECTOR lowering for size

Summary:
Implements custom lowering logic that finds the optimal value for the
initial splat of the vector and either uses it or uses v128.const if
it is available and if it would produce smaller code. This logic
replaces large TableGen ISEL patterns that would lower all non-splat
BUILD_VECTORs into a splat followed by a fixed number of replace_lane
instructions. This CL fixes PR39685.

Reviewers: aheejin

Subscribers: dschuff, sbc100, jgravelle-google, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D56633

llvm-svn: 352592
4 files changed
tree: 9e3f9060cb92547d474b3563e3d334cb9bbf111b
  1. clang/
  2. clang-tools-extra/
  3. compiler-rt/
  4. debuginfo-tests/
  5. libclc/
  6. libcxx/
  7. libcxxabi/
  8. libunwind/
  9. lld/
  10. lldb/
  11. llgo/
  12. llvm/
  13. openmp/
  14. parallel-libs/
  15. polly/
  16. pstl/
  17. .arcconfig
  18. .clang-format
  19. .clang-tidy
  20. README.md
README.md

The LLVM Compiler Infrastructure

This directory and its subdirectories contain source code for LLVM, a toolkit for the construction of highly optimized compilers, optimizers, and runtime environments.