[PATCH] D71065: [ARM][MVE] Add intrinsics for immediate shifts.

[Simon Tatham via Phabricator via cfe-commits]

simon_tatham created this revision.
simon_tatham added reviewers: dmgreen, miyuki, MarkMurrayARM, ostannard.
Herald added subscribers: llvm-commits, cfe-commits, hiraditya, kristof.beyls.
Herald added projects: clang, LLVM.

This adds the family of `vshlq_n` and `vshrq_n` ACLE intrinsics, which
shift every lane of a vector left or right by a compile-time
immediate. They mostly work by expanding to the IR `shl`, `lshr` and
`ashr` operations, with their second operand being a vector splat of
the immediate.

There's a fiddly special case, though. ACLE specifies that the
immediate in `vshrq_n` can take values up to //and including// the bit
size of the vector lane. But LLVM IR thinks that shifting right by the
full size of the lane is UB, and feels free to replace the `lshr` with
an `undef` half way through the optimization pipeline. Hence, to keep
this legal in source code, I have to detect it at codegen time.
Logical (unsigned) right shifts by the element size are handled by
simply emitting the zero vector; arithmetic ones are converted into a
shift of one bit less, which will always give the same output.

In order to do that check, I also had to enhance the tablegen
MveEmitter so that it can cope with converting a builtin function's
operand into a bare integer to pass to a code-generating subfunction.
Previously the only bare integers it knew how to handle were flags
generated from within `arm_mve.td`.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D71065

Files:
  clang/include/clang/Basic/arm_mve.td
  clang/include/clang/Basic/arm_mve_defs.td
  clang/lib/CodeGen/CGBuiltin.cpp
  clang/test/CodeGen/arm-mve-intrinsics/vector-shift-imm.c
  clang/utils/TableGen/MveEmitter.cpp
  llvm/include/llvm/IR/IntrinsicsARM.td
  llvm/lib/Target/ARM/ARMInstrMVE.td
  llvm/test/CodeGen/Thumb2/mve-intrinsics/vector-shift-imm.ll

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