[flang-commits] [flang] [flang] Expand SUM(DIM=CONSTANT) into an hlfir.elemental. (PR #118556)

[Slava Zakharin via flang-commits]

vzakhari wrote:

I tried reproducing it today on grace with `-mtune=neoverse-v1`, but with no luck.  I could not use `-flto`, because I did not have `LLVMgold.so` plugin readily available. With `-flto` there is no perf difference, though I see the assembly changes in `digits_2` for the only case of `SUM(DIM)` - it looks like a complete unroll of 8x9 loop nest.

@tblah by any chance can you confirm that the regression appears only with `-flto`?  I will build the plugin and try it myself, but not until tomorrow.  If you get regression without `-flto`, then I will need to find the right testing machine.

In the meantime, I disabled the simplification by default in #119287.

https://github.com/llvm/llvm-project/pull/118556