Revert "Revert i586 fix, fix test instead"

This reverts commit 1ea2f12.

Author: calebzulawski

crates/core_simd/src/reduction.rs

@@ -59,13 +59,23 @@ macro_rules! impl_float_reductions {
             /// Produces the sum of the lanes of the vector.
             #[inline]
             pub fn sum(self) -> $scalar {
-                unsafe { crate::intrinsics::simd_reduce_add_ordered(self, 0.) }
+                // f32 SIMD sum is inaccurate on i586
+                if cfg!(all(target_arch = "x86", not(target_feature = "sse2"))) && core::mem::size_of::<$scalar>() == 4 {
+                    self.as_slice().iter().sum()
+                } else {
+                    unsafe { crate::intrinsics::simd_reduce_add_ordered(self, 0.) }
+                }
             }
 
             /// Produces the sum of the lanes of the vector.
             #[inline]
             pub fn product(self) -> $scalar {
-                unsafe { crate::intrinsics::simd_reduce_mul_ordered(self, 1.) }
+                // f32 SIMD product is inaccurate on i586
+                if cfg!(all(target_arch = "x86", not(target_feature = "sse2"))) && core::mem::size_of::<$scalar>() == 4 {
+                    self.as_slice().iter().product()
+                } else {
+                    unsafe { crate::intrinsics::simd_reduce_mul_ordered(self, 1.) }
+                }
             }
 
             /// Returns the maximum lane in the vector.

crates/core_simd/tests/ops_macros.rs

@@ -483,7 +483,7 @@ macro_rules! impl_float_tests {
                     test_helpers::test_1(&|x| {
                         test_helpers::prop_assert_biteq! (
                             Vector::<LANES>::from_array(x).sum(),
-                            x.iter().sum(),
+                            x.iter().copied().fold(0 as Scalar, <Scalar as core::ops::Add>::add),
                         );
                         Ok(())
                     });
@@ -493,7 +493,7 @@ macro_rules! impl_float_tests {
                     test_helpers::test_1(&|x| {
                         test_helpers::prop_assert_biteq! (
                             Vector::<LANES>::from_array(x).product(),
-                            x.iter().product(),
+                            x.iter().copied().fold(1. as Scalar, <Scalar as core::ops::Mul>::mul),
                         );
                         Ok(())
                     });