[PATCH] D28629: [SCEV] Limit recursion depth of constant evolving

[Michael Liao via Phabricator via llvm-commits]

hliao added a comment.

I collected the maximum depth of 'getConstantEvolvingPHIOperands' when it returns successfully or otherwise. Here is the statistics collected on SingleSource, MultiSource, and External (spec2000 and spec2006).

- when 'getConstantEvolvingPHIOperands' returns null

| MAX-DEPTH-PER-CUNIT | NUM-OF-CUNITS |
| ------------------- | ------------- |
| 0                   | 103           |
| 1                   | 169           |
| 2                   | 653           |
| 3                   | 187           |
| 4                   | 145           |
| 5                   | 76            |
| 6                   | 65            |
| 7                   | 18            |
| 8                   | 94            |
| 9                   | 5             |
| 10                  | 12            |
| 11                  | 10            |
| 12                  | 5             |
| 13                  | 3             |



- when 'getConstantEvolvingPHIOperands' return non-null

| MAX-DEPTH-PER-CUNIT | NUM-OF-CUNITS |
| ------------------- | ------------- |
| 0                   | 159           |
| 1                   | 323           |
| 2                   | 502           |
| 3                   | 218           |
| 4                   | 546           |
| 5                   | 167           |
| 6                   | 100           |
| 7                   | 49            |
| 8                   | 432           |
| 9                   | 46            |
| 10                  | 29            |
| 11                  | 10            |
| 12                  | 4             |
| 13                  | 10            |
| 16                  | 1             |
| 17                  | 3             |
| 18                  | 1             |
| 19                  | 1             |

It sounds to me that 32 is a reasonable choice.


Repository:
  rL LLVM

https://reviews.llvm.org/D28629