[llvm] 1e260f9 - [LICM][docs] Document that LICM is also a canonicalization transform. NFC.

[Philip Reames via llvm-commits]

Thank you for adding the documentation!

Philip

On 12/8/20 3:57 AM, Sjoerd Meijer via llvm-commits wrote:
> Author: Sjoerd Meijer
> Date: 2020-12-08T11:56:35Z
> New Revision: 1e260f955d3123351fc68de8c2dde02b1be6d14f
>
> URL: https://github.com/llvm/llvm-project/commit/1e260f955d3123351fc68de8c2dde02b1be6d14f
> DIFF: https://github.com/llvm/llvm-project/commit/1e260f955d3123351fc68de8c2dde02b1be6d14f.diff
>
> LOG: [LICM][docs] Document that LICM is also a canonicalization transform. NFC.
>
> This documents that LICM is a canonicalization transform, which we discussed
> recently in:
>
> http://lists.llvm.org/pipermail/llvm-dev/2020-December/147184.html
>
> but which was also discused earlier, e.g. in:
>
> http://lists.llvm.org/pipermail/llvm-dev/2019-September/135058.html
>
> Added:
>      
>
> Modified:
>      llvm/docs/Passes.rst
>      llvm/lib/Transforms/Scalar/LICM.cpp
>
> Removed:
>      
>
>
> ################################################################################
> diff  --git a/llvm/docs/Passes.rst b/llvm/docs/Passes.rst
> index 202e3ab223d6..d146ce745282 100644
> --- a/llvm/docs/Passes.rst
> +++ b/llvm/docs/Passes.rst
> @@ -720,6 +720,12 @@ into the preheader block, or by sinking code to the exit blocks if it is safe.
>   This pass also promotes must-aliased memory locations in the loop to live in
>   registers, thus hoisting and sinking "invariant" loads and stores.
>   
> +Hoisting operations out of loops is a canonicalization transform. It enables
> +and simplifies subsequent optimizations in the middle-end. Rematerialization
> +of hoisted instructions to reduce register pressure is the responsibility of
> +the back-end, which has more accurate information about register pressure and
> +also handles other optimizations than LICM that increase live-ranges.
> +
>   This pass uses alias analysis for two purposes:
>   
>   #. Moving loop invariant loads and calls out of loops.  If we can determine
>
> diff  --git a/llvm/lib/Transforms/Scalar/LICM.cpp b/llvm/lib/Transforms/Scalar/LICM.cpp
> index 9d90986c54ad..1b14bc972a9e 100644
> --- a/llvm/lib/Transforms/Scalar/LICM.cpp
> +++ b/llvm/lib/Transforms/Scalar/LICM.cpp
> @@ -12,6 +12,13 @@
>   // safe.  This pass also promotes must-aliased memory locations in the loop to
>   // live in registers, thus hoisting and sinking "invariant" loads and stores.
>   //
> +// Hoisting operations out of loops is a canonicalization transform.  It
> +// enables and simplifies subsequent optimizations in the middle-end.
> +// Rematerialization of hoisted instructions to reduce register pressure is the
> +// responsibility of the back-end, which has more accurate information about
> +// register pressure and also handles other optimizations than LICM that
> +// increase live-ranges.
> +//
>   // This pass uses alias analysis for two purposes:
>   //
>   //  1. Moving loop invariant loads and calls out of loops.  If we can determine
>
>
>          
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