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f47d325eec
AliasSetTracker::addUnknown may create an AliasSet devoid of pointers just to contain an instruction if no suitable AliasSet already exists. It will then AliasSet::addUnknownInst and we will be done. However, it's possible for addUnknown to choose an existing AliasSet to addUnknownInst. If this were to occur, we are in a bit of a pickle: removing pointers from the AliasSet can cause the entire AliasSet to become destroyed, taking our unknown instructions out with them. Instead, keep track whether or not our AliasSet has any unknown instructions. This fixes PR21582. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222338 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))
//===---------------------------------------------------------------------===//