================
@@ -755,6 +769,43 @@ bool llvm::validateDelinearizationResult(ScalarEvolution
&SE,
if (!isKnownLessThan(&SE, Subscript, Size))
return false;
}
+
+ // The offset computation is as follows:
+ //
+ // Offset = I_n +
+ // S_n * I_{n-1} +
+ // ... +
+ // (S_2 * ... * S_n) * I_1
+ //
+ // Regarding this as a function from (I_1, I_2, ..., I_n) to integers, it
+ // must be injective. To guarantee it, the above calculation must not
+ // overflow. Since we have already checked that 0 <= I_k < S_k for k = 2..n,
+ // the minimum and maximum values occur in the following cases:
+ //
+ // Min = [I_1][0]...[0] = S_2 * ... * S_n * I_1
+ // Max = [I_1][S_2-1]...[S_n-1]
+ // = (S_2 * ... * S_n) * I_1 +
+ // (S_2 * ... * S_{n-1}) * (S_2 - 1) +
+ // ... +
+ // (S_n - 1)
+ // = (S_2 * ... * S_n) * I_1 +
----------------
Meinersbur wrote:
```suggestion
// = (S_2 * ... * S_n) * I_1 + /* this is the same as Min expression;
if this expression has already been checked for overlflow, need only check the
rest of the expression for Max */
```
Some cleverness I did not see (`Min == Prod * I_1`). I was expecting someting
more symmetric. My suggested comment here is clunky, maby you find something
better.
https://github.com/llvm/llvm-project/pull/169902
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