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* [gcc r14-1712] simplify-rtx: Implement constant folding of SS_TRUNCATE, US_TRUNCATE
@ 2023-06-12 12:25 Kyrylo Tkachov
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From: Kyrylo Tkachov @ 2023-06-12 12:25 UTC (permalink / raw)
To: gcc-cvs
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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