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Fix a corner case in fcvt_to_sint.i32.f64 legalization.

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An f64 can represent multiple values in the range INT_MIN-1 < x <=
INT_MIN which all truncate to INT_MIN, so comparing the input value
against INT_MIN is not good enough.

Instead, detect overflow on x <= INT_MIN-1 when INT_MIN-1 is an exact
floating point value.
This commit is contained in:
Jakob Stoklund Olesen
2017-09-28 14:24:39 -07:00
parent 8abcdac5a1
commit 2888ff5bf3
2 changed files with 19 additions and 13 deletions
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8
lib/cretonne/src/ir/immediates.rs
View File

@@ -6,11 +6,9 @@
//! module in the meta language. //! module in the meta language.
use std::fmt::{self, Display, Formatter}; use std::fmt::{self, Display, Formatter};
use std::{i32, u32};
use std::str::FromStr;
#[cfg(test)]
use std::mem; use std::mem;
use std::str::FromStr;
use std::{i32, u32};
/// 64-bit immediate integer operand. /// 64-bit immediate integer operand.
/// ///
@@ -547,7 +545,6 @@ impl Ieee32 {
} }
/// Create a new `Ieee32` representing the number `x`. /// Create a new `Ieee32` representing the number `x`.
#[cfg(test)]
pub fn with_float(x: f32) -> Ieee32 { pub fn with_float(x: f32) -> Ieee32 {
Ieee32(unsafe { mem::transmute(x) }) Ieee32(unsafe { mem::transmute(x) })
} }
@@ -600,7 +597,6 @@ impl Ieee64 {
} }
/// Create a new `Ieee64` representing the number `x`. /// Create a new `Ieee64` representing the number `x`.
#[cfg(test)]
pub fn with_float(x: f64) -> Ieee64 { pub fn with_float(x: f64) -> Ieee64 {
Ieee64(unsafe { mem::transmute(x) }) Ieee64(unsafe { mem::transmute(x) })
} }

24
lib/cretonne/src/isa/intel/enc_tables.rs
View File

@@ -222,15 +222,25 @@ fn expand_fcvt_to_sint(inst: ir::Inst, func: &mut ir::Function, cfg: &mut Contro
); );
// Check for case 1: INT_MIN is the correct result. // Check for case 1: INT_MIN is the correct result.
// We use a `ueq` condition here because that can be translated into a single branch, and we // Determine the smallest floating point number that would convert to INT_MIN.
// already know that we don't have a NaN. let mut overflow_cc = FloatCC::LessThan;
let fintmin = match xty { let output_bits = ty.lane_bits();
ir::types::F32 => pos.ins().f32const(Ieee32::pow2(ty.lane_bits() - 1).neg()), let flimit = match xty {
ir::types::F64 => pos.ins().f64const(Ieee64::pow2(ty.lane_bits() - 1).neg()), ir::types::F32 => pos.ins().f32const(Ieee32::pow2(output_bits - 1).neg()),
ir::types::F64 => {
// An f64 can represent `i32::min_value() - 1` exactly with precision to spare, so
// there are values less than -2^(N-1) that convert correctly to INT_MIN.
pos.ins().f64const(if output_bits < 64 {
overflow_cc = FloatCC::LessThanOrEqual;
Ieee64::with_float(-((1u64 << (output_bits - 1)) as f64) - 1.0)
} else {
Ieee64::pow2(output_bits - 1).neg()
})
}
_ => panic!("Can't convert {}", xty), _ => panic!("Can't convert {}", xty),
}; };
let in_range = pos.ins().fcmp(FloatCC::UnorderedOrEqual, x, fintmin); let overflow = pos.ins().fcmp(overflow_cc, x, flimit);
pos.ins().trapz(in_range, ir::TrapCode::IntegerOverflow); pos.ins().trapnz(overflow, ir::TrapCode::IntegerOverflow);
pos.ins().jump(done, &[]); pos.ins().jump(done, &[]);
pos.insert_ebb(done); pos.insert_ebb(done);