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Fix float min and max operations in presence of NaN
Cranelift's fmin and fmax instructions propagate NaN, while Rust's min and max don't. Fixes rust-lang#1049
1 parent e0b9f3b commit c6564f8

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5 files changed

+23
-60
lines changed

5 files changed

+23
-60
lines changed

‎patches/0001-stdsimd-Disable-unsupported-tests.patch

Lines changed: 0 additions & 16 deletions
Original file line numberDiff line numberDiff line change
@@ -124,22 +124,6 @@ index cb39e73..fc0ebe1 100644
124124

125125
fn sqrt<const LANES: usize>() {
126126
test_helpers::test_unary_elementwise(
127-
@@ -491,6 +493,7 @@ macro_rules! impl_float_tests {
128-
)
129-
}
130-
131-
+ /*
132-
fn min<const LANES: usize>() {
133-
// Regular conditions (both values aren't zero)
134-
test_helpers::test_binary_elementwise(
135-
@@ -536,6 +539,7 @@ macro_rules! impl_float_tests {
136-
assert!(p_zero.max(n_zero).to_array().iter().all(|x| *x == 0.));
137-
assert!(n_zero.max(p_zero).to_array().iter().all(|x| *x == 0.));
138-
}
139-
+ */
140-
141-
fn clamp<const LANES: usize>() {
142-
test_helpers::test_3(&|value: [Scalar; LANES], mut min: [Scalar; LANES], mut max: [Scalar; LANES]| {
143127
@@ -581,6 +585,7 @@ macro_rules! impl_float_tests {
144128
});
145129
}

‎patches/0023-sysroot-Ignore-failing-tests.patch

Lines changed: 0 additions & 40 deletions
Original file line numberDiff line numberDiff line change
@@ -46,45 +46,5 @@ index 4bc44e9..8e3c7a4 100644
4646

4747
#[test]
4848
fn cell_allows_array_cycle() {
49-
diff --git a/library/core/tests/num/mod.rs b/library/core/tests/num/mod.rs
50-
index a17c094..5bb11d2 100644
51-
--- a/library/core/tests/num/mod.rs
52-
+++ b/library/core/tests/num/mod.rs
53-
@@ -651,11 +651,12 @@ macro_rules! test_float {
54-
assert_eq!((9.0 as $fty).min($neginf), $neginf);
55-
assert_eq!(($neginf as $fty).min(-9.0), $neginf);
56-
assert_eq!((-9.0 as $fty).min($neginf), $neginf);
57-
- assert_eq!(($nan as $fty).min(9.0), 9.0);
58-
- assert_eq!(($nan as $fty).min(-9.0), -9.0);
59-
- assert_eq!((9.0 as $fty).min($nan), 9.0);
60-
- assert_eq!((-9.0 as $fty).min($nan), -9.0);
61-
- assert!(($nan as $fty).min($nan).is_nan());
62-
+ // Cranelift fmin has NaN propagation
63-
+ //assert_eq!(($nan as $fty).min(9.0), 9.0);
64-
+ //assert_eq!(($nan as $fty).min(-9.0), -9.0);
65-
+ //assert_eq!((9.0 as $fty).min($nan), 9.0);
66-
+ //assert_eq!((-9.0 as $fty).min($nan), -9.0);
67-
+ //assert!(($nan as $fty).min($nan).is_nan());
68-
}
69-
#[test]
70-
fn max() {
71-
@@ -673,11 +674,12 @@ macro_rules! test_float {
72-
assert_eq!((9.0 as $fty).max($neginf), 9.0);
73-
assert_eq!(($neginf as $fty).max(-9.0), -9.0);
74-
assert_eq!((-9.0 as $fty).max($neginf), -9.0);
75-
- assert_eq!(($nan as $fty).max(9.0), 9.0);
76-
- assert_eq!(($nan as $fty).max(-9.0), -9.0);
77-
- assert_eq!((9.0 as $fty).max($nan), 9.0);
78-
- assert_eq!((-9.0 as $fty).max($nan), -9.0);
79-
- assert!(($nan as $fty).max($nan).is_nan());
80-
+ // Cranelift fmax has NaN propagation
81-
+ //assert_eq!(($nan as $fty).max(9.0), 9.0);
82-
+ //assert_eq!(($nan as $fty).max(-9.0), -9.0);
83-
+ //assert_eq!((9.0 as $fty).max($nan), 9.0);
84-
+ //assert_eq!((-9.0 as $fty).max($nan), -9.0);
85-
+ //assert!(($nan as $fty).max($nan).is_nan());
86-
}
87-
#[test]
88-
fn rem_euclid() {
8949
--
9050
2.21.0 (Apple Git-122)

‎scripts/tests.sh

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -139,6 +139,7 @@ function extended_sysroot_tests() {
139139

140140
pushd stdsimd
141141
echo "[TEST] rust-lang/stdsimd"
142+
../build/cargo clean
142143
../build/cargo build --all-targets --target $TARGET_TRIPLE
143144
if [[ "$HOST_TRIPLE" = "$TARGET_TRIPLE" ]]; then
144145
../build/cargo test -q

‎src/intrinsics/mod.rs

Lines changed: 20 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1029,23 +1029,39 @@ pub(crate) fn codegen_intrinsic_call<'tcx>(
10291029
ret.write_cvalue(fx, old);
10301030
};
10311031

1032+
// In Rust floating point min and max don't propagate NaN. In Cranelift they do however.
1033+
// For this reason it is necessary to use `a.is_nan() ? b : (a >= b ? b : a)` for `minnumf*`
1034+
// and `a.is_nan() ? b : (a <= b ? b : a)` for `maxnumf*`. NaN checks are done by comparing
1035+
// a float against itself. Only in case of NaN is it not equal to itself.
10321036
minnumf32, (v a, v b) {
1033-
let val = fx.bcx.ins().fmin(a, b);
1037+
let a_is_nan = fx.bcx.ins().fcmp(FloatCC::NotEqual, a, a);
1038+
let a_ge_b = fx.bcx.ins().fcmp(FloatCC::GreaterThanOrEqual, a, b);
1039+
let temp = fx.bcx.ins().select(a_ge_b, b, a);
1040+
let val = fx.bcx.ins().select(a_is_nan, b, temp);
10341041
let val = CValue::by_val(val, fx.layout_of(fx.tcx.types.f32));
10351042
ret.write_cvalue(fx, val);
10361043
};
10371044
minnumf64, (v a, v b) {
1038-
let val = fx.bcx.ins().fmin(a, b);
1045+
let a_is_nan = fx.bcx.ins().fcmp(FloatCC::NotEqual, a, a);
1046+
let a_ge_b = fx.bcx.ins().fcmp(FloatCC::GreaterThanOrEqual, a, b);
1047+
let temp = fx.bcx.ins().select(a_ge_b, b, a);
1048+
let val = fx.bcx.ins().select(a_is_nan, b, temp);
10391049
let val = CValue::by_val(val, fx.layout_of(fx.tcx.types.f64));
10401050
ret.write_cvalue(fx, val);
10411051
};
10421052
maxnumf32, (v a, v b) {
1043-
let val = fx.bcx.ins().fmax(a, b);
1053+
let a_is_nan = fx.bcx.ins().fcmp(FloatCC::NotEqual, a, a);
1054+
let a_le_b = fx.bcx.ins().fcmp(FloatCC::LessThanOrEqual, a, b);
1055+
let temp = fx.bcx.ins().select(a_le_b, b, a);
1056+
let val = fx.bcx.ins().select(a_is_nan, b, temp);
10441057
let val = CValue::by_val(val, fx.layout_of(fx.tcx.types.f32));
10451058
ret.write_cvalue(fx, val);
10461059
};
10471060
maxnumf64, (v a, v b) {
1048-
let val = fx.bcx.ins().fmax(a, b);
1061+
let a_is_nan = fx.bcx.ins().fcmp(FloatCC::NotEqual, a, a);
1062+
let a_le_b = fx.bcx.ins().fcmp(FloatCC::LessThanOrEqual, a, b);
1063+
let temp = fx.bcx.ins().select(a_le_b, b, a);
1064+
let val = fx.bcx.ins().select(a_is_nan, b, temp);
10491065
let val = CValue::by_val(val, fx.layout_of(fx.tcx.types.f64));
10501066
ret.write_cvalue(fx, val);
10511067
};

‎src/intrinsics/simd.rs

Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -378,6 +378,7 @@ pub(super) fn codegen_simd_intrinsic_call<'tcx>(
378378
};
379379

380380
simd_reduce_min, (c v) {
381+
// FIXME support floats
381382
validate_simd_type!(fx, intrinsic, span, v.layout().ty);
382383
simd_reduce(fx, v, None, ret, |fx, layout, a, b| {
383384
let lt = fx.bcx.ins().icmp(if layout.ty.is_signed() {
@@ -390,6 +391,7 @@ pub(super) fn codegen_simd_intrinsic_call<'tcx>(
390391
};
391392

392393
simd_reduce_max, (c v) {
394+
// FIXME support floats
393395
validate_simd_type!(fx, intrinsic, span, v.layout().ty);
394396
simd_reduce(fx, v, None, ret, |fx, layout, a, b| {
395397
let gt = fx.bcx.ins().icmp(if layout.ty.is_signed() {

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