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From: Kyrylo Tkachov <ktkachov@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org Subject: [gcc r14-1712] simplify-rtx: Implement constant folding of SS_TRUNCATE, US_TRUNCATE Date: Mon, 12 Jun 2023 12:25:56 +0000 (GMT) [thread overview] Message-ID: <20230612122556.8352E38582B7@sourceware.org> (raw) https://gcc.gnu.org/g:921b841350c4fc298d09f6c5674663e0f4208610 commit r14-1712-g921b841350c4fc298d09f6c5674663e0f4208610 Author: Kyrylo Tkachov <kyrylo.tkachov@arm.com> Date: Mon Jun 12 11:42:29 2023 +0100 simplify-rtx: Implement constant folding of SS_TRUNCATE, US_TRUNCATE This patch implements RTL constant-folding for the SS_TRUNCATE and US_TRUNCATE codes. The semantics are a clamping operation on the argument with the min and max of the narrow mode, followed by a truncation. The signedness of the clamp and the min/max extrema is derived from the signedness of the saturating operation. We have a number of instructions in aarch64 that use SS_TRUNCATE and US_TRUNCATE to represent their operations and we have pretty thorough runtime tests in gcc.target/aarch64/advsimd-intrinsics/vqmovn*.c. With this patch the instructions are folded away at optimisation levels and the correctness checks still pass. Bootstrapped and tested on aarch64-none-linux-gnu and aarch64_be-none-elf. gcc/ChangeLog: * simplify-rtx.cc (simplify_const_unary_operation): Handle US_TRUNCATE, SS_TRUNCATE. Diff: --- gcc/simplify-rtx.cc | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/gcc/simplify-rtx.cc b/gcc/simplify-rtx.cc index 276be67aa67..21b7eb484d0 100644 --- a/gcc/simplify-rtx.cc +++ b/gcc/simplify-rtx.cc @@ -2131,6 +2131,20 @@ simplify_const_unary_operation (enum rtx_code code, machine_mode mode, result = wide_int::from (op0, width, UNSIGNED); break; + case US_TRUNCATE: + case SS_TRUNCATE: + { + signop sgn = code == US_TRUNCATE ? UNSIGNED : SIGNED; + wide_int nmax + = wide_int::from (wi::max_value (width, sgn), + GET_MODE_PRECISION (imode), sgn); + wide_int nmin + = wide_int::from (wi::min_value (width, sgn), + GET_MODE_PRECISION (imode), sgn); + result = wi::min (wi::max (op0, nmin, sgn), nmax, sgn); + result = wide_int::from (result, width, sgn); + break; + } case SIGN_EXTEND: result = wide_int::from (op0, width, SIGNED); break;
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