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8ef7b17dfc
This is the first commit in a series that add an @llvm.assume intrinsic which can be used to provide the optimizer with a condition it may assume to be true (when the control flow would hit the intrinsic call). Some basic properties are added here: - llvm.invariant(true) is dead. - llvm.invariant(false) is unreachable (this directly corresponds to the documented behavior of MSVC's __assume(0)), so is llvm.invariant(undef). The intrinsic is tagged as writing arbitrarily, in order to maintain control dependencies. BasicAA has been updated, however, to return NoModRef for any particular location-based query so that we don't unnecessarily block code motion. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@213973 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))
//===---------------------------------------------------------------------===//