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Because we do not constant fold multiplications in SimplifyFMAMul, we match 1.0 and 0.0 for both operands, as multiplying by them is guaranteed to produce an exact result (if it is allowed to do so). Note that it is not enough to just swap the operands to ensure a constant is on the RHS, as we want to also cover the case with 2 constants. Reviewers: lebedev.ri, spatel, reames, scanon Reviewed By: lebedev.ri, reames Differential Revision: https://reviews.llvm.org/D67553 llvm-svn: 372915
Analysis Opportunities:
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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))
//===---------------------------------------------------------------------===//