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9f141640b5
Summary: This patch updates TargetTransformInfoImplCRTPBase::getGEPCost to consider addressing modes. It now returns TCC_Free when the GEP can be completely folded to an addresing mode. I started this patch as I refactored SLSR. Function isGEPFoldable looks common and is indeed used by some WIP of mine. So I extracted that logic to getGEPCost. Furthermore, I noticed getGEPCost wasn't directly tested anywhere. The best testing bed seems CostModel, but its getInstructionCost method invokes getAddressComputationCost for GEPs which provides very coarse estimation. So this patch also makes getInstructionCost call the updated getGEPCost for GEPs. This change inevitably breaks some tests because the cost model changes, but nothing looks seriously wrong -- if we believe the new cost model is the right way to go, these tests should be updated. This patch is not perfect yet -- the comments in some tests need to be updated. I want to know whether this is a right approach before fixing those details. Reviewers: chandlerc, hfinkel Subscribers: aschwaighofer, llvm-commits, aemerson Differential Revision: http://reviews.llvm.org/D9819 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@243250 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))
//===---------------------------------------------------------------------===//