On Fri, 4 Feb 2022, Richard Biener via Gcc-patches wrote: > This adds explicit variable birth CLOBBERs in an attempt to fix > PR90348 and duplicates. The birth / death CLOBBER pairs are > used to compute liveness and conflicts for stack variable > coalescing where the lack of an explicit birth but instead > use of first mention causes misrepresentation of variable life > ranges when optimization moves the first mention upwards the > original birth point at the variables bind expression start.
I'm not clear on exactly where you consider a variable to be born, but note that non-VLA C variables have a lifetime that starts at the beginning of their block, not at their declaration: it's valid to jump backward from after the declaration to before it and then access the variable via a pointer, or jump forward again over the declaration and access it by name. (Most programs of course don't do that sort of thing.) -- Joseph S. Myers jos...@codesourcery.com
