[PATCH] D61461: When removing inalloca, convert to static alloca

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

> Teach instcombine or another general cleanup pass to turn an inalloca alloca static if there are no inalloca calls anywhere in the current function

Given an arbitrary alloca in a function with no inalloca calls, hoisting the alloca to the entry block requires proving that the allocation's lifetime doesn't overlap itself.  For example, we have to make sure we don't miscompile `for (int i = 0; i < n; i++) foo(alloca(1));`.  So you have to track stacksave + stackrestore levels anyway.

That said, a general alloca hoisting transform might be useful in other contexts, and analyzing the whole function at once is probably the most efficient way to handle it.


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https://reviews.llvm.org/D61461