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6e9e89f482
DemandedBits and BDCE currently only support scalar integers. This patch extends them to also handle vector integer operations. In this case bits are not tracked for individual vector elements, instead a bit is demanded if it is demanded for any of the elements. This matches the behavior of computeKnownBits in ValueTracking and SimplifyDemandedBits in InstCombine. The getDemandedBits() method can now only be called on instructions that have integer or vector of integer type. Previously it could be called on any sized instruction (even if it was not particularly useful). The size of the return value is now always the scalar size in bits (while previously it was the type size in bits). Differential Revision: https://reviews.llvm.org/D55297 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@348549 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))
//===---------------------------------------------------------------------===//