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optimize u128/i128 popcounts further #354

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Merged
merged 1 commit into from
Oct 19, 2023
Merged

optimize u128/i128 popcounts further #354

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25 changes: 15 additions & 10 deletions src/intrinsic/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,7 @@ mod simd;
#[cfg(feature="master")]
use std::iter;

use gccjit::{BinaryOp, ComparisonOp, Function, RValue, ToRValue, Type, UnaryOp, FunctionType};
use gccjit::{ComparisonOp, Function, RValue, ToRValue, Type, UnaryOp, FunctionType};
use rustc_codegen_ssa::MemFlags;
use rustc_codegen_ssa::base::wants_msvc_seh;
use rustc_codegen_ssa::common::IntPredicate;
Expand Down Expand Up @@ -819,7 +819,9 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
value
};

if value_type.is_u128(&self.cx) {
// only break apart 128-bit ints if they're not natively supported
// TODO(antoyo): remove this if/when native 128-bit integers land in libgccjit
if value_type.is_u128(&self.cx) && !self.cx.supports_128bit_integers {
let sixty_four = self.gcc_int(value_type, 64);
let right_shift = self.gcc_lshr(value, sixty_four);
let high = self.gcc_int_cast(right_shift, self.cx.ulonglong_type);
Expand All @@ -842,30 +844,33 @@ impl<'a, 'gcc, 'tcx> Builder<'a, 'gcc, 'tcx> {
let counter_type = self.int_type;
let counter = self.current_func().new_local(None, counter_type, "popcount_counter");
let val = self.current_func().new_local(None, value_type, "popcount_value");
let zero = self.context.new_rvalue_zero(counter_type);
let zero = self.gcc_zero(counter_type);
self.llbb().add_assignment(None, counter, zero);
self.llbb().add_assignment(None, val, value);
self.br(loop_head);

// check if value isn't zero
self.switch_to_block(loop_head);
let zero = self.context.new_rvalue_zero(value_type);
let cond = self.context.new_comparison(None, ComparisonOp::NotEquals, val.to_rvalue(), zero);
let zero = self.gcc_zero(value_type);
let cond = self.gcc_icmp(IntPredicate::IntNE, val.to_rvalue(), zero);
self.cond_br(cond, loop_body, loop_tail);

// val &= val - 1;
self.switch_to_block(loop_body);
let sub = val.to_rvalue() - self.context.new_rvalue_one(value_type);
loop_body.add_assignment_op(None, val, BinaryOp::BitwiseAnd, sub);
let one = self.gcc_int(value_type, 1);
let sub = self.gcc_sub(val.to_rvalue(), one);
let op = self.gcc_and(val.to_rvalue(), sub);
loop_body.add_assignment(None, val, op);

// counter += 1
let one = self.context.new_rvalue_one(counter_type);
loop_body.add_assignment_op(None, counter, BinaryOp::Plus, one);
let one = self.gcc_int(counter_type, 1);
let op = self.gcc_add(counter.to_rvalue(), one);
loop_body.add_assignment(None, counter, op);
self.br(loop_head);

// end of loop
self.switch_to_block(loop_tail);
self.context.new_cast(None, counter.to_rvalue(), result_type)
self.gcc_int_cast(counter.to_rvalue(), result_type)
}

// Algorithm from: https://blog.regehr.org/archives/1063
Expand Down