Tom Eccles bdacd56fd1 [flang][CodeGen] add nsw to address calculations (#74709) ...

`nsw` is a flag for LLVM arithmetic operations meaning "no signed wrap".
If this keyword is present, the result of the operation is a poison
value if overflow occurs. Adding this keyword permits LLVM to re-order
integer arithmetic more aggressively.

In

https://discourse.llvm.org/t/rfc-changes-to-fircg-xarray-coor-codegen-to-allow-better-hoisting/75257/16
@vzakhari observed that adding nsw is useful to enable hoisting of
address calculations after some loops (or is at least a step in that
direction).

Classic flang also adds nsw to address calculations.

2023-12-08 10:51:20 +00:00

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