| Issue |
153507
|
| Summary |
[GVN] Redundant loads in stencil loops
|
| Labels |
missed-optimization,
llvm:GVN
|
| Assignees |
vzakhari
|
| Reporter |
vzakhari
|
The small reproducers below are insipired by `CPU2000/172.mgrid` code from `resid` routine. LLVM is not able to fully optimize redundant loads in loops accessing adjacent elements, e.g. `a(i-1)+a(i)+a(i+1)`.
Here is the most simple example for 1D array: https://godbolt.org/z/cacGdbhnr
Here, GVN is able to optimize only one load, but fails to optimize the second one.
A more complex example with a 2D array: https://godbolt.org/z/EboxdG5ae
Here, GVN is not able to optimize any of the loads.
The actual `172.mgrid` code uses 3D arrays.
I tried to allow `Add` operations with non-constant operands in `canPHITrans`, `PHITransAddr::translateSubExpr` and `PHITransAddr::insertTranslatedSubExpr`, but GVN bails out early during the memory dependencies computations in the 2D case.
I will appreciate any suggestions how to tackle this problem, and any hints!
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