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35c4e071be
logic to look through pointer casts, making them trivially stronger in the face of loads and stores with intervening pointer casts. I've included a few test cases that demonstrate the kind of folding instcombine can do without pointer casts and then variations which obfuscate the logic through bitcasts. Without this patch, the variations all fail to optimize fully. This is more important now than it has been in the past as I've started moving the load canonicialization to more closely follow the value type requirements rather than the pointer type requirements and thus this needs to be prepared for more pointer casts. When I made the same change to stores several test cases regressed without logic along these lines so I wanted to systematically improve matters first. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@220178 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))
//===---------------------------------------------------------------------===//