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The issue here is that we actually allow CGSCC passes to mutate IR (and therefore invalidate analyses) outside of the current SCC. At a minimum, we need to support mutating parent and ancestor SCCs to support the ArgumentPromotion pass which rewrites all calls to a function. However, the analysis invalidation infrastructure is heavily based around not needing to invalidate the same IR-unit at multiple levels. With Loop passes for example, they don't invalidate other Loops. So we need to customize how we handle CGSCC invalidation. Doing this without gratuitously re-running analyses is even harder. I've avoided most of these by using an out-of-band preserved set to accumulate the cross-SCC invalidation, but it still isn't perfect in the case of re-visiting the same SCC repeatedly *but* it coming off the worklist. Unclear how important this use case really is, but I wanted to call it out. Another wrinkle is that in order for this to successfully propagate to function analyses, we have to make sure we have a proxy from the SCC to the Function level. That requires pre-creating the necessary proxy. The motivating test case now works cleanly and is added for ArgumentPromotion. Thanks for the review from Philip and Wei! Differential Revision: https://reviews.llvm.org/D59869 llvm-svn: 357137
Analysis Opportunities:
//===---------------------------------------------------------------------===//
In test/Transforms/LoopStrengthReduce/quadradic-exit-value.ll, the
ScalarEvolution expression for %r is this:
{1,+,3,+,2}<loop>
Outside the loop, this could be evaluated simply as (%n * %n), however
ScalarEvolution currently evaluates it as
(-2 + (2 * (trunc i65 (((zext i64 (-2 + %n) to i65) * (zext i64 (-1 + %n) to i65)) /u 2) to i64)) + (3 * %n))
In addition to being much more complicated, it involves i65 arithmetic,
which is very inefficient when expanded into code.
//===---------------------------------------------------------------------===//
In formatValue in test/CodeGen/X86/lsr-delayed-fold.ll,
ScalarEvolution is forming this expression:
((trunc i64 (-1 * %arg5) to i32) + (trunc i64 %arg5 to i32) + (-1 * (trunc i64 undef to i32)))
This could be folded to
(-1 * (trunc i64 undef to i32))
//===---------------------------------------------------------------------===//