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cd13a3808a
(Re-apply r234361 with a fix and a testcase for PR23157) Both run-time pointer checking and the dependence analysis are capable of dealing with uniform addresses. I.e. it's really just an orthogonal property of the loop that the analysis computes. Run-time pointer checking will only try to reason about SCEVAddRec pointers or else gives up. If the uniform pointer turns out the be a SCEVAddRec in an outer loop, the run-time checks generated will be correct (start and end bounds would be equal). In case of the dependence analysis, we work again with SCEVs. When compared against a loop-dependent address of the same underlying object, the difference of the two SCEVs won't be constant. This will result in returning an Unknown dependence for the pair. When compared against another uniform access, the difference would be constant and we should return the right type of dependence (forward/backward/etc). The changes also adds support to query this property of the loop and modify the vectorizer to use this. Patch by Ashutosh Nema! git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@234424 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))
//===---------------------------------------------------------------------===//