[llvm] [HashRecognize] Prevent values other than `ComputedValue` from exiting loop (PR #213080)

[Sean Clarke via llvm-commits]

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@@ -578,12 +578,7 @@ std::variant<PolynomialInfo, StringRef> HashRecognize::recognizeCRC() const {
                    : LHS->getType()->getIntegerBitWidth()))
     return "Loop iterations exceed bitwidth of data";
 
-  // Make sure that the computed value is used in the exit block: this should be
-  // true even if it is only really used in an outer loop's exit block, since
-  // the loop is in LCSSA form.
   auto *ComputedValue = cast<SelectInst>(ConditionalRecurrence.Step);
-  if (Exit->phis().empty())
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xarkenz wrote:

I'm not sure "`Found stray incoming values in loop exit block`" is a fitting error message for it, unless you would suggest reporting a different message. I would think the containsUnreachable check is sufficient for catching side effects since we don't permit that even if `ComputedValue` is used in the exit block.

https://github.com/llvm/llvm-project/pull/213080