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3659b8adc9
Summary: This patch allows phi nodes like %x = phi [ %incptr, ... ] [ %var, ... ] %incptr = getelementptr %x, 1 to be analyzed by BasicAliasAnalysis. In aliasPHI, we can detect incoming values that are recursive GEPs with a constant offset. Instead of trying to analyze a recursive GEP (and failing), we now ignore it and instead set the size of the memory referenced by the PHINode to UnknownSize. This represents all the possible memory locations the pointer represented by the PHINode could be advanced to by the GEP. For now, this new behavior is turned off by default to allow debugging of performance degradations seen with SPEC/x86 and Hexagon benchmarks. The flag -basicaa-recphi turns it on. Reviewers: hfinkel, sanjoy Subscribers: tobiasvk_caf, sanjoy, llvm-commits Differential Revision: http://reviews.llvm.org/D10368 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@242320 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))
//===---------------------------------------------------------------------===//