[PATCH 2/2][AArch64] Simplify+improve patterns for ushr(d?)_n_u64 intrinsic
Mon Sep 8 16:25:00 GMT 2014
Similarly, the ushr_n_u64 and ushrd_n_u64 intrinsics, allow to perform an
unsigned-shift-right of a 64-bit value by 64 places. This is not supported by
the standard lshr pattern, which masks the shift amount with 63. However, a
shift-by-64 always produces zero, so this patch moves in a constant 0 rather
than outputting a shift instruction.
Cross-tested on aarch64-none-elf and aarch64_be-none-elf, with test coverage
provided by gcc.target/aarch64/ushr64_1.c .
* config/aarch64/aarch64-simd.md (aarch64_lshr_simddi): Handle shift
by 64 by moving const0_rtx.
* config/aarch64/aarch64.md (enum unspec): Delete UNSPEC_USHR64.
Alan Lawrence wrote:
> The sshr_n_64 intrinsics allow performing a signed shift right by 64 places. The
> standard ashrdi3 pattern masks the sign amount with 63, so cannot be used.
> However, such a shift fills the result by the sign bit, which is identical to
> shifting right by 63. This patch just simplifies the code to shift by 63
> instead, which allows to remove an UNSPEC and insn previously dedicated to this
> Cross-tested on aarch64-none-elf and aarch64_be-none-elf, with test coverage
> provided by gcc.target/aarch64/sshr64_1.c .
> * config/aarch64/aarch64.md (enum "unspec"): Remove UNSPEC_SSHR64.
> * config/aarch64/aarch64-simd.md (aarch64_ashr_simddi): Change shift
> amount to 63 if was 64.
> (aarch64_sshr_simddi): Remove.
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