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different fields. We can show that two GEPs off of the same (possibly multidimensional) array of structs, into different fields, can't alias. Quoting: For two GEPOperators GEP1 and GEP2, if we find that: - both GEPs begin indexing from the exact same pointer; - the last indices in both GEPs are constants, indexing into a struct; - said indices are different, hence,the pointed-to fields are different; - and both GEPs only index through arrays prior to that; this lets us determine that the struct that GEP1 indexes into and the struct that GEP2 indexes into must either precisely overlap or be completely disjoint. Because they cannot partially overlap, indexing into different non-overlapping fields of the struct will never alias. The other BasicAA::aliasGEP rules worked in some cases, but not all (for example, the i32x3 struct in the testcase). We can add this simple ad-hoc rule to complement them. rdar://19717375 Differential Revision: http://reviews.llvm.org/D7453 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@228498 91177308-0d34-0410-b5e6-96231b3b80d8
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))
//===---------------------------------------------------------------------===//