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b3b970744d
Imported functions and variable get the visibility from the module supplying the definition. However, non-imported definitions do not get the visibility from (ELF) the most constraining visibility among all modules (Mach-O) the visibility of the prevailing definition. This patch * adds visibility bits to GlobalValueSummary::GVFlags * computes the result visibility and propagates it to all definitions Protected/hidden can imply dso_local which can enable some optimizations (this is stronger than GVFlags::DSOLocal because the implied dso_local can be leveraged for ELF -shared while default visibility dso_local has to be cleared for ELF -shared). Note: we don't have summaries for declarations, so for ELF if a declaration has the most constraining visibility, the result visibility may not be that one. Differential Revision: https://reviews.llvm.org/D92900
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))
//===---------------------------------------------------------------------===//