[PATCH] D152068: (WIP) [InstCombine] add overflow checking on AddSub

[Kohei Asano via Phabricator via llvm-commits]

khei4 created this revision.
khei4 added a reviewer: nikic.
Herald added subscribers: StephenFan, hiraditya.
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khei4 requested review of this revision.
Herald added a project: LLVM.
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proof: https://alive2.llvm.org/ce/z/W7RXmY

part of https://reviews.llvm.org/D146903

TODO: write description


https://reviews.llvm.org/D152068

Files:
  llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp


Index: llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1996,11 +1996,11 @@
 
     // C-(X+C2) --> (C-C2)-X
     if (match(Op1, m_Add(m_Value(X), m_ImmConstant(C2)))) {
-      // c - c2 is overflow?
-      bool HasNSW = false;
+      // C-C2, C-(X+C2), (X+C2) never overflow=> (C-C2)-X never overflow
       BinaryOperator *Res =
           BinaryOperator::CreateSub(ConstantExpr::getSub(C, C2), X);
-      Res->setHasNoSignedWrap(HasNSW);
+      // TODO: check C-(X+C2) and (X+C2)'s overflow
+      Res->setHasNoSignedWrap(willNotOverflowSignedSub(C, C2, *Res));
       return Res;
     }
   }


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