Revision - 146c2ba - Fix backpropagation of conditionals when the type is later widened - origin: https://github.com/JuliaLang/julia

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19 April 2024, 06:28:37 UTC

Revision 146c2bab4fd9fb0c3ea6af47fe08c796a6407949 authored by Keno Fischer on 16 January 2018, 18:56:21 UTC, committed by Keno Fischer on 16 January 2018, 19:07:03 UTC

Fix backpropagation of conditionals when the type is later widened

Consider the following example:

```
f() = (1, 1)
f(s) = i == 1 ? (1, 2) : nothing
function foo()
    next = f()
    while next !== nothing
        next = f(Core.getfield(next, 2))
    end
end
```

This was causing unnecessary allocations, because inference failed
to inform codegen that the reference to next inside the loop was
guaranteed not to be Nothing. Ironically if f() could also have
returned nothing, inference was able to figure this out, thanks to
pass the result of the comparison was inferred as Const(true),
and on the second pass as Conditional(next, Tuple{Int, Int}, Const(nothing)),
the tmerge of which is Bool. Fix that by
implementing Jameson's suggestion in #25261, and instead infering
the first pass as Conditional(next, Tuple{Int, Int}, Union{}).
To make this work we also adjust the lattice relation to have
Conditional(next, T, Union{}) ⊑ Const(true). The result is that
the result of the comparison does not get widened to Bool as
quickly, retaining the type information on next and allowing
codegen to emit efficient code.

1 parent aea9155

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Tip revision: 146c2bab4fd9fb0c3ea6af47fe08c796a6407949 authored by Keno Fischer on 16 January 2018, 18:56:21 UTC
Fix backpropagation of conditionals when the type is later widened

Tip revision: 146c2ba

File	Mode	Size
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doc
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.gitignore	-rw-r--r--	213 bytes
.mailmap	-rw-r--r--	9.5 KB
.travis.yml	-rw-r--r--	6.5 KB
CONTRIBUTING.md	-rw-r--r--	20.4 KB
DISTRIBUTING.md	-rw-r--r--	23.6 KB
HISTORY.md	-rw-r--r--	144.9 KB
LICENSE.md	-rw-r--r--	5.5 KB
Make.inc	-rw-r--r--	35.2 KB
Makefile	-rw-r--r--	26.4 KB
NEWS.md	-rw-r--r--	62.9 KB
README.arm.md	-rw-r--r--	5.7 KB
README.md	-rw-r--r--	28.1 KB
README.windows.md	-rw-r--r--	13.0 KB
VERSION	-rw-r--r--	10 bytes
Windows.inc	-rw-r--r--	1.5 KB
appveyor.yml	-rw-r--r--	2.2 KB

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Fix backpropagation of conditionals when the type is later widened

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