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Reland [SimplifyCFG] Delete the unnecessary range check for small mask operation #70542

Merged
merged 2 commits into from
Nov 3, 2023
Merged

Reland [SimplifyCFG] Delete the unnecessary range check for small mask operation #70542

merged 2 commits into from
Nov 3, 2023

Commits on Nov 2, 2023

  1. [SimplifyCFG] Delete the unnecessary range check for small mask opera… 

    …tion

When the small mask value little than 64, we can eliminate the checking
for upper limit of the range by enlarge the lookup table size to the maximum
index value. (Then the final table size grows to the next pow2 value)
```
bool f(unsigned x) {
    switch (x % 8) {
        case 0: return 1;
        case 1: return 0;
        case 2: return 0;
        case 3: return 1;
        case 4: return 1;
        case 5: return 0;
        case 6: return 1;

        // This would remove the range check: case 7: return 0;
    }
    return 0;
}
```
Use WouldFitInRegister instead of fitsInLegalInteger to support
more result type beside bool.

Fixes llvm#65120
    @vfdff
    vfdff committed Nov 2, 2023
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  2. [SimplifyCFG] Fix the compile crash when default branch is unreachable 

    This modification will squash to the previous commit if accepted.
Seperate it just to make it more clearly to review.
    @vfdff
    vfdff committed Nov 2, 2023
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