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The patch is to partially fix PR10584. Correlated Value Propagation queries LVI to check non-null for pointer params of each callsite. If we know the def of param is an alloca instruction, we know it is non-null and can return early from LVI. Similarly, CVP queries LVI to check whether pointer for each mem access is constant. If the def of the pointer is an alloca instruction, we know it is not a constant pointer. These shortcuts can reduce the cost of CVP significantly. Differential Revision: https://reviews.llvm.org/D18066 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@281586 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))
//===---------------------------------------------------------------------===//