[llvm] [LAA,Loads] Use loop guards and max BTC if needed when checking deref. (PR #155672)

[Florian Hahn via llvm-commits]

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@@ -2338,23 +2338,15 @@ bool ScalarEvolution::willNotOverflow(Instruction::BinaryOps BinOp, bool Signed,
   // Can we use context to prove the fact we need?
   if (!CtxI)
     return false;
+  // TODO: Support mul.
+  if (BinOp == Instruction::Mul)
+    return false;
   auto *RHSC = dyn_cast<SCEVConstant>(RHS);
   // TODO: Lift this limitation.
   if (!RHSC)
     return false;
   APInt C = RHSC->getAPInt();
   unsigned NumBits = C.getBitWidth();
-  if (BinOp == Instruction::Mul) {
-    // Multiplying by 0 or 1 never overflows
-    if (C.isZero() || C.isOne())
-      return true;
-    if (Signed)
-      return false;
-    APInt Limit = APInt::getMaxValue(NumBits).udiv(C);
-    // To avoid overflow, we need to make sure that LHS <= MAX / C.
-    return isKnownPredicateAt(ICmpInst::ICMP_ULE, LHS, getConstant(Limit),
-                              CtxI);
-  }
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fhahn wrote:

That would be great. If there are, could you add them?

https://github.com/llvm/llvm-project/pull/155672