[compiler-rt] Add missing carry to 128x128->256 wide multiply #97257
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The addition
r0 + (r1 << 64)
when calculatinglo
can overflow. This PR makes sure the overflow is carried intohi
.Credit to @marthadev for the Rust version of this fix in rust-lang/compiler-builtins#587 (comment).
I've tested the fix works locally. I've also added a test to this PR for the fix, although I can't run it locally as the
__multf3
test is only run on platforms wherelong double
is f128.(Note to reviewer: I don't have commit access)
Fixes #90009
Fixes #91840