[AC] Handle (X+C1)<C2 assumes (PR48408)

InstCombine canonicalizes X>C && X<C' style comparisons into
(X+C1)<C2. This type of expression is recognized by some analyses
like LVI, but currently not when used inside assumptions, because
AssumptionCache does not track affected values for it.

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/AssumptionCache.cpp b/llvm/lib/Analysis/AssumptionCache.cpp
index fdde5ea..cb94f71 100644
--- a/llvm/lib/Analysis/AssumptionCache.cpp
+++ b/llvm/lib/Analysis/AssumptionCache.cpp
@@ -115,6 +115,14 @@ findAffectedValues(CallInst *CI,
       AddAffectedFromEq(A);
       AddAffectedFromEq(B);
     }
+
+    Value *X;
+    // Handle (A + C1) u< C2, which is the canonical form of A > C3 && A < C4,
+    // and recognized by LVI at least.
+    if (Pred == ICmpInst::ICMP_ULT &&
+        match(A, m_Add(m_Value(X), m_ConstantInt())) &&
+        match(B, m_ConstantInt()))
+      AddAffected(X);
   }
 }