On Mon, 25 Mar 2024, Chenghui Pan wrote:
> Current document of Tree SSA passes contains many parts that is not
> updated for many years.
>
> This patch removes some info that is outdated and not existed in
> current GCC codebase, and fixes some wrong code location descriptions
> based on current codebase status and ChangeLogs.
OK
Thanks,
Richard.
> Changes since v1: Add correct info for pass_build_alias.
>
> gcc/ChangeLog:
>
> * doc/passes.texi: Correction of Tree SSA Passes info.
> ---
> gcc/doc/passes.texi | 75 +++++----------------------------------------
> 1 file changed, 7 insertions(+), 68 deletions(-)
>
> diff --git a/gcc/doc/passes.texi b/gcc/doc/passes.texi
> index b50d3d5635b..b13ad06c5a9 100644
> --- a/gcc/doc/passes.texi
> +++ b/gcc/doc/passes.texi
> @@ -450,17 +450,6 @@ The following briefly describes the Tree optimization
> passes that are
> run after gimplification and what source files they are located in.
>
> @itemize @bullet
> -@item Remove useless statements
> -
> -This pass is an extremely simple sweep across the gimple code in which
> -we identify obviously dead code and remove it. Here we do things like
> -simplify @code{if} statements with constant conditions, remove
> -exception handling constructs surrounding code that obviously cannot
> -throw, remove lexical bindings that contain no variables, and other
> -assorted simplistic cleanups. The idea is to get rid of the obvious
> -stuff quickly rather than wait until later when it's more work to get
> -rid of it. This pass is located in @file{tree-cfg.cc} and described by
> -@code{pass_remove_useless_stmts}.
>
> @item OpenMP lowering
>
> @@ -478,7 +467,7 @@ described by @code{pass_lower_omp}.
>
> If OpenMP generation (@option{-fopenmp}) is enabled, this pass expands
> parallel regions into their own functions to be invoked by the thread
> -library. The pass is located in @file{omp-low.cc} and is described by
> +library. The pass is located in @file{omp-expand.cc} and is described by
> @code{pass_expand_omp}.
>
> @item Lower control flow
> @@ -511,15 +500,6 @@ This pass decomposes a function into basic blocks and
> creates all of
> the edges that connect them. It is located in @file{tree-cfg.cc} and
> is described by @code{pass_build_cfg}.
>
> -@item Find all referenced variables
> -
> -This pass walks the entire function and collects an array of all
> -variables referenced in the function, @code{referenced_vars}. The
> -index at which a variable is found in the array is used as a UID
> -for the variable within this function. This data is needed by the
> -SSA rewriting routines. The pass is located in @file{tree-dfa.cc}
> -and is described by @code{pass_referenced_vars}.
> -
> @item Enter static single assignment form
>
> This pass rewrites the function such that it is in SSA form. After
> @@ -562,15 +542,6 @@ variables that are used once into the expression that
> uses them and
> seeing if the result can be simplified. It is located in
> @file{tree-ssa-forwprop.cc} and is described by @code{pass_forwprop}.
>
> -@item Copy Renaming
> -
> -This pass attempts to change the name of compiler temporaries involved in
> -copy operations such that SSA->normal can coalesce the copy away. When
> compiler
> -temporaries are copies of user variables, it also renames the compiler
> -temporary to the user variable resulting in better use of user symbols. It
> is
> -located in @file{tree-ssa-copyrename.c} and is described by
> -@code{pass_copyrename}.
> -
> @item PHI node optimizations
>
> This pass recognizes forms of PHI inputs that can be represented as
> @@ -581,12 +552,8 @@ It is located in @file{tree-ssa-phiopt.cc} and is
> described by
> @item May-alias optimization
>
> This pass performs a flow sensitive SSA-based points-to analysis.
> -The resulting may-alias, must-alias, and escape analysis information
> -is used to promote variables from in-memory addressable objects to
> -non-aliased variables that can be renamed into SSA form. We also
> -update the @code{VDEF}/@code{VUSE} memory tags for non-renameable
> -aggregates so that we get fewer false kills. The pass is located
> -in @file{tree-ssa-alias.cc} and is described by @code{pass_may_alias}.
> +It is located in @file{tree-ssa-structalias.cc} and is described
> +by @code{pass_build_alias}.
>
> Interprocedural points-to information is located in
> @file{tree-ssa-structalias.cc} and described by @code{pass_ipa_pta}.
> @@ -604,7 +571,7 @@ is described by @code{pass_ipa_tree_profile}.
> This pass implements series of heuristics to guess propababilities
> of branches. The resulting predictions are turned into edge profile
> by propagating branches across the control flow graphs.
> -The pass is located in @file{tree-profile.cc} and is described by
> +The pass is located in @file{predict.cc} and is described by
> @code{pass_profile}.
>
> @item Lower complex arithmetic
> @@ -653,7 +620,7 @@ in @file{tree-ssa-math-opts.cc} and is described by
> @item Full redundancy elimination
>
> This is a simpler form of PRE that only eliminates redundancies that
> -occur on all paths. It is located in @file{tree-ssa-pre.cc} and
> +occur on all paths. It is located in @file{tree-ssa-sccvn.cc} and
> described by @code{pass_fre}.
>
> @item Loop optimization
> @@ -708,7 +675,7 @@ to align the number of iterations, and to align the
> memory accesses in the
> loop.
> The pass is implemented in @file{tree-vectorizer.cc} (the main driver),
> @file{tree-vect-loop.cc} and @file{tree-vect-loop-manip.cc} (loop specific
> parts
> -and general loop utilities), @file{tree-vect-slp} (loop-aware SLP
> +and general loop utilities), @file{tree-vect-slp.cc} (loop-aware SLP
> functionality), @file{tree-vect-stmts.cc}, @file{tree-vect-data-refs.cc} and
> @file{tree-vect-slp-patterns.cc} containing the SLP pattern matcher.
> Analysis of data references is in @file{tree-data-ref.cc}.
> @@ -755,10 +722,6 @@ the ``copy-of'' relation. It eliminates redundant
> copies from the
> code. The pass is located in @file{tree-ssa-copy.cc} and described by
> @code{pass_copy_prop}.
>
> -A related pass that works on memory copies, and not just register
> -copies, is located in @file{tree-ssa-copy.cc} and described by
> -@code{pass_store_copy_prop}.
> -
> @item Value range propagation
>
> This transformation is similar to constant propagation but
> @@ -811,14 +774,6 @@ run last so that we have as much time as possible to
> prove that the
> statement is not reachable. It is located in @file{tree-cfg.cc} and
> is described by @code{pass_warn_function_return}.
>
> -@item Leave static single assignment form
> -
> -This pass rewrites the function such that it is in normal form. At
> -the same time, we eliminate as many single-use temporaries as possible,
> -so the intermediate language is no longer GIMPLE, but GENERIC@. The
> -pass is located in @file{tree-outof-ssa.cc} and is described by
> -@code{pass_del_ssa}.
> -
> @item Merge PHI nodes that feed into one another
>
> This is part of the CFG cleanup passes. It attempts to join PHI nodes
> @@ -857,25 +812,9 @@ pass is located in @file{tree-object-size.cc} and is
> described by
> @item Loop invariant motion
>
> This pass removes expensive loop-invariant computations out of loops.
> -The pass is located in @file{tree-ssa-loop.cc} and described by
> +The pass is located in @file{tree-ssa-loop-im.cc} and described by
> @code{pass_lim}.
>
> -@item Loop nest optimizations
> -
> -This is a family of loop transformations that works on loop nests. It
> -includes loop interchange, scaling, skewing and reversal and they are
> -all geared to the optimization of data locality in array traversals
> -and the removal of dependencies that hamper optimizations such as loop
> -parallelization and vectorization. The pass is located in
> -@file{tree-loop-linear.c} and described by
> -@code{pass_linear_transform}.
> -
> -@item Removal of empty loops
> -
> -This pass removes loops with no code in them. The pass is located in
> -@file{tree-ssa-loop-ivcanon.cc} and described by
> -@code{pass_empty_loop}.
> -
> @item Unrolling of small loops
>
> This pass completely unrolls loops with few iterations. The pass
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)
