[PATCH] D129643: [SCEV] Use context to strengthen flags of BinOps

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev created this revision.
mkazantsev added reviewers: nikic, lebedev.ri, skatkov, reames.
Herald added subscribers: javed.absar, zzheng, hiraditya.
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Sometimes SCEV cannot infer nuw/nsw from something as simple as

    len in [0, MAX_INT]
  ...
    iv = phi(0, iv.next)
    guard(iv <s len)
    guard(iv <u len)
    iv.next = iv + 1

just because flag strenthening only relies on definition and does not use local facts.
This patch adds support for the simplest case: inference of flags of `add(x, constant)`
if we can contextually prove that `x <= max_int - constant`.

In case if it has negative CT impact, there is an option to disable this logic. I woudln't
expect that though.


https://reviews.llvm.org/D129643

Files:
  llvm/include/llvm/Analysis/ScalarEvolution.h
  llvm/lib/Analysis/ScalarEvolution.cpp
  llvm/test/Transforms/IndVarSimplify/AArch64/widen-loop-comp.ll
  llvm/test/Transforms/IndVarSimplify/X86/iv-widen.ll
  llvm/test/Transforms/IndVarSimplify/X86/pr35406.ll
  llvm/test/Transforms/IndVarSimplify/bbi-63564.ll
  llvm/test/Transforms/IndVarSimplify/cycled_phis.ll
  llvm/test/Transforms/IndVarSimplify/eliminate-comparison.ll
  llvm/test/Transforms/IndVarSimplify/finite-exit-comparisons.ll
  llvm/test/Transforms/IndVarSimplify/loop-predication.ll
  llvm/test/Transforms/IndVarSimplify/trivial-guard.ll
  llvm/test/Transforms/LoopUnroll/runtime-loop-multiple-exits.ll

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