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When hoisting the allocas with a constant integer size, the constant integer was moved to where the alloca is hoisted to unconditionally. By CodeGen there have been various iterations of mlir canonicalization and dead code elimination. This can cause lots of unrelated bits of code to share the same constant values. If for some reason the alloca couldn't be hoisted all of the way to the entry block of the function, moving the constant might result in it no-longer dominating some of the remaining uses. In theory, there should be dominance analysis to ensure the location of the constant does dominate all uses of it. But those constants are effectively free anyway (they aren't even separate instructions in LLVM IR), so it is less expensive just to leave the old one where it was and insert a new one we know for sure is immediately before the alloca.
Flang
Flang is a ground-up implementation of a Fortran front end written in modern C++. It started off as the f18 project (https://github.com/flang-compiler/f18) with an aim to replace the previous flang project (https://github.com/flang-compiler/flang) and address its various deficiencies. F18 was subsequently accepted into the LLVM project and rechristened as Flang.
Please note that flang is not ready yet for production usage.
Getting Started
Read more about flang in the docs directory. Start with the compiler overview.
To better understand Fortran as a language and the specific grammar accepted by flang, read Fortran For C Programmers and flang's specifications of the Fortran grammar and the OpenMP grammar.
Treatment of language extensions is covered in this document.
To understand the compilers handling of intrinsics, see the discussion of intrinsics.
To understand how a flang program communicates with libraries at runtime, see the discussion of runtime descriptors.
If you're interested in contributing to the compiler, read the style guide and also review how flang uses modern C++ features.
If you are interested in writing new documentation, follow LLVM's Markdown style guide.
Consult the Getting Started with Flang for information on building and running flang.