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Merge pull request #1086 from rtfeldman/multiple-of-overflow

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fix overflow issue in Num.isMultipleOf
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Richard Feldman 2021-03-19 21:14:40 -04:00 • committed by GitHub
commit 9adf42a6b2
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2 changed files with 58 additions and 26 deletions
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67
compiler/gen/src/llvm/build.rs
View file

@ -4779,44 +4779,73 @@ fn build_int_binop<'a, 'ctx, 'env>(
NumLte => bd.build_int_compare(SLE, lhs, rhs, "int_lte").into(),
NumRemUnchecked => bd.build_int_signed_rem(lhs, rhs, "rem_int").into(),
NumIsMultipleOf => {
/* this builds the following construct
if rhs != 0 {
let rem = lhs % rhs;
rem == 0
} else {
// rhs == 0 && lhs ==0
lhs == 0
}
*/
// this builds the following construct
//
// if (rhs == 0 || rhs == -1) {
// // lhs is a multiple of rhs iff
// //
// // - rhs == -1
// // - both rhs and lhs are 0
// //
// // the -1 case is important for overflow reasons `isize::MIN % -1` crashes in rust
// (rhs == -1) || (lhs == 0)
// } else {
// let rem = lhs % rhs;
// rem == 0
// }
//
// NOTE we'd like the branches to be swapped for better branch prediciton,
// but llvm normalizes to the above ordering in -O3
let zero = rhs.get_type().const_zero();
let condition_rhs = bd.build_int_compare(IntPredicate::NE, rhs, zero, "is_zero_rhs");
let condition_lhs = bd.build_int_compare(IntPredicate::EQ, lhs, zero, "is_zero_lhs");
let neg_1 = rhs.get_type().const_int(-1i64 as u64, false);
let current_block = bd.get_insert_block().unwrap(); //block that we are in right now;
let then_block = env.context.append_basic_block(parent, "then");
let special_block = env.context.append_basic_block(parent, "special_block");
let default_block = env.context.append_basic_block(parent, "default_block");
let cont_block = env.context.append_basic_block(parent, "branchcont");
bd.build_conditional_branch(condition_rhs, then_block, cont_block);
bd.build_switch(
rhs,
default_block,
&[(zero, special_block), (neg_1, special_block)],
);
bd.position_at_end(then_block);
let condition_rem = {
bd.position_at_end(default_block);
let rem = bd.build_int_signed_rem(lhs, rhs, "int_rem");
let condition_rem = bd.build_int_compare(IntPredicate::EQ, rem, zero, "is_zero_rem");
let result = bd.build_int_compare(IntPredicate::EQ, rem, zero, "is_zero_rem");
bd.build_unconditional_branch(cont_block);
result
};
let condition_special = {
bd.position_at_end(special_block);
let is_zero = bd.build_int_compare(IntPredicate::EQ, lhs, zero, "is_zero_lhs");
let is_neg_one =
bd.build_int_compare(IntPredicate::EQ, rhs, neg_1, "is_neg_one_rhs");
let result = bd.build_or(is_neg_one, is_zero, "cond");
bd.build_unconditional_branch(cont_block);
result
};
{
bd.position_at_end(cont_block);
let phi = bd.build_phi(env.context.bool_type(), "branch");
phi.add_incoming(&[
(&condition_rem, then_block),
(&condition_lhs, current_block),
(&condition_rem, default_block),
(&condition_special, special_block),
]);
phi.as_basic_value()
}
}
NumDivUnchecked => bd.build_int_signed_div(lhs, rhs, "div_int").into(),
NumPowInt => call_bitcode_fn(env, &[lhs.into(), rhs.into()], &bitcode::NUM_POW_INT),
NumBitwiseAnd => bd.build_and(lhs, rhs, "int_bitwise_and").into(),

3
compiler/test_gen/src/gen_num.rs
View file

@ -1389,5 +1389,8 @@ mod gen_num {
// false
assert_evals_to!("Num.isMultipleOf 5 2", false, bool);
assert_evals_to!("Num.isMultipleOf 5 0", false, bool);
// overflow
assert_evals_to!("Num.isMultipleOf -9223372036854775808 -1", true, bool);
}
}