[PATCH] D152068: [InstCombine] add overflow checking on AddSub `C-(X+C2) --> (C-C2)-X`

[Kohei Asano via Phabricator via llvm-commits]

khei4 updated this revision to Diff 528115.
khei4 retitled this revision from "(WIP) [InstCombine] add overflow checking on AddSub" to "[InstCombine] add overflow checking on AddSub `C-(X+C2) --> (C-C2)-X`".
khei4 edited the summary of this revision.
khei4 added a reviewer: spatel.

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D152068/new/

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 +1996,13 @@
 
     // 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);
+      auto *OBO1 = cast<OverflowingBinaryOperator>(Op1);
+      Res->setHasNoSignedWrap(I.hasNoSignedWrap() &&
+                              OBO1->hasNoUnsignedWrap() &&
+                              willNotOverflowSignedSub(C, C2, *Res));
       return Res;
     }
   }


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