[flang] Added LoopInvariantCodeMotion pass for [HL]FIR. (#173438)
The new pass allows hoisting some `fir.load` operations early
in MLIR. For example, many descriptor load might be hoisted
out of the loops, though it does not make much difference
in performance, because LLVM is able to optimize such loads
(which are lowered as `llvm.memcpy` into temporary descriptors),
given that proper TBAA information is generated by Flang.
Further hoisting improvements are possible in [HL]FIR LICM,
e.g. getting proper mod-ref results for Fortran runtime calls
may allow hoisting loads from global variables, which LLVM
cannot do due to lack of alias information.
This patch also contains improvements for FIR mod-ref analysis:
We may recurse into `HasRecursiveMemoryEffects` operations and
use `getModRef` recursively to get more precise results for
regions with `fir.call` operations.
This patch also modifies `AliasAnalysis` to set the instantiation
point for cases where the tracked data is accessed through a load
from `!fir.ref<!fir.box<>>`: without this change the mod-ref
analysis was not able to recognize user pointer/allocatable variables.
llvm-project
0bf4df8b - [flang] Added LoopInvariantCodeMotion pass for [HL]FIR. (#173438)
