Use f{32,64}::to_bits for is_zero test in vec::SpecFromElem #49466
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vec::SpecFromElem provides an optimization to use calloc to fill a Vec when the element given to fill the Vec is represented by 0. For floats, the test for that currently used is `x == 0. && x.is_sign_positive()`. When compiled in a standalone function, rustc generates the following assembly: ``` xorps xmm1, xmm1 ucomisd xmm0, xmm1 setnp al sete cl and cl, al movq rax, xmm0 test rax, rax setns al and al, cl ret ``` A simpler test telling us whether the value is represented by 0, is `x.to_bits() == 0`, which rustc compiles to: ``` movq rax, xmm0 test rax, rax sete al ret ``` Not that the test is hot in any way, but it also makes it clearer what the intent in the rust code is.
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Use f{32,64}::to_bits for is_zero test in vec::SpecFromElem
vec::SpecFromElem provides an optimization to use calloc to fill a Vec
when the element given to fill the Vec is represented by 0.
For floats, the test for that currently used is `x == 0. &&
x.is_sign_positive()`. When compiled in a standalone function, rustc
generates the following assembly:
```
xorps xmm1, xmm1
ucomisd xmm0, xmm1
setnp al
sete cl
and cl, al
movq rax, xmm0
test rax, rax
setns al
and al, cl
ret
```
A simpler test telling us whether the value is represented by 0, is
`x.to_bits() == 0`, which rustc compiles to:
```
movq rax, xmm0
test rax, rax
sete al
ret
```
Not that the test is hot in any way, but it also makes it clearer what
the intent in the rust code is.
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vec::SpecFromElem provides an optimization to use calloc to fill a Vec
when the element given to fill the Vec is represented by 0.
For floats, the test for that currently used is
x == 0. && x.is_sign_positive(). When compiled in a standalone function, rustcgenerates the following assembly:
A simpler test telling us whether the value is represented by 0, is
x.to_bits() == 0, which rustc compiles to:Not that the test is hot in any way, but it also makes it clearer what
the intent in the rust code is.