[PATCH] D104634: [SCEV] Generalize MatchBinaryAddToConst to support non-add expressions.

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev added inline comments.


================
Comment at: llvm/lib/Analysis/ScalarEvolution.cpp:10106
   case ICmpInst::ICMP_SLE:
-    // X s<= (X + C)<nsw> if C >= 0
-    if (MatchBinaryAddToConst(RHS, LHS, C, SCEV::FlagNSW) && C.isNonNegative())
+    // (X + C1)<nsw> s<= (X + C2) if C1 s<= C2.
+    if (MatchBinaryAddToConst(LHS, RHS, C1, C2, SCEV::FlagNSW) && C1.sle(C2))
----------------
mkazantsev wrote:
> Is lack of `nsw` in `(X + C2)` intentional? If yes, the counter-example to this is
> 
> ```
> X = SINT_MIN
> C1 = 1
> C2 = -1
> ```
> `(X + C1)<nsw> = SINT_MIN + 1 <= (X - 1) = SINT_MAX`, but obviously `C1 > C2`.
> 
> 
I'm not sure whether two-ways implication is required here, or one way implication is enough. It was two-ways in old code. If I'm wrong here, please let me know.


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  https://reviews.llvm.org/D104634/new/

https://reviews.llvm.org/D104634