[gcc/devel/subreg-coalesce] df: Add -ftrack-subreg-liveness option

[Lehua Ding <lhtin@gcc.gnu.org>]

https://gcc.gnu.org/g:b6b50e19f88bd33b6c0d252795ebb6cffda9574f

commit b6b50e19f88bd33b6c0d252795ebb6cffda9574f
Author: Lehua Ding <lehua.ding@rivai.ai>
Date:   Tue Jan 30 16:45:25 2024 +0800

    df: Add -ftrack-subreg-liveness option
    
    Add new flag -ftrack-subreg-liveness to enable track-subreg-liveness.
    This flag is enabled at -O3/fast.
    
    gcc/ChangeLog:
    
            * common.opt: add -ftrack-subreg-liveness option.
            * opts.cc: auto aneble -ftrack-subreg-liveness in -O3/fast

Diff:
---
 gcc/common.opt      | 4 ++++
 gcc/common.opt.urls | 3 +++
 gcc/doc/invoke.texi | 8 ++++++++
 gcc/opts.cc         | 1 +
 4 files changed, 16 insertions(+)

diff --git a/gcc/common.opt b/gcc/common.opt
index ad348844775..bd030973434 100644
--- a/gcc/common.opt
+++ b/gcc/common.opt
@@ -2157,6 +2157,10 @@ fira-share-spill-slots
 Common Var(flag_ira_share_spill_slots) Init(1) Optimization
 Share stack slots for spilled pseudo-registers.
 
+ftrack-subreg-liveness
+Common Var(flag_track_subreg_liveness) Init(0) Optimization
+Track subreg liveness information.
+
 fira-verbose=
 Common RejectNegative Joined UInteger Var(flag_ira_verbose) Init(5)
 -fira-verbose=<number>	Control IRA's level of diagnostic messages.
diff --git a/gcc/common.opt.urls b/gcc/common.opt.urls
index f71ed80a34b..59f27a6f7c6 100644
--- a/gcc/common.opt.urls
+++ b/gcc/common.opt.urls
@@ -880,6 +880,9 @@ UrlSuffix(gcc/Optimize-Options.html#index-fira-share-save-slots)
 fira-share-spill-slots
 UrlSuffix(gcc/Optimize-Options.html#index-fira-share-spill-slots)
 
+ftrack-subreg-liveness
+UrlSuffix(gcc/Optimize-Options.html#index-ftrack-subreg-liveness)
+
 fira-verbose=
 UrlSuffix(gcc/Developer-Options.html#index-fira-verbose)
 
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
index 27c31ab0c86..9724cbb32ba 100644
--- a/gcc/doc/invoke.texi
+++ b/gcc/doc/invoke.texi
@@ -13186,6 +13186,14 @@ Disable sharing of stack slots allocated for pseudo-registers.  Each
 pseudo-register that does not get a hard register gets a separate
 stack slot, and as a result function stack frames are larger.
 
+@opindex ftrack-subreg-liveness
+@item -ftrack-subreg-liveness
+Enable tracking subreg liveness information. This infomation allows IRA
+and LRA to support subreg coalesce feature which can improve the quality
+of register allocation.
+
+This option is enabled at level @option{-O3} for all targets.
+
 @opindex flra-remat
 @item -flra-remat
 Enable CFG-sensitive rematerialization in LRA.  Instead of loading
diff --git a/gcc/opts.cc b/gcc/opts.cc
index a90dc57f8b5..7b5d905a241 100644
--- a/gcc/opts.cc
+++ b/gcc/opts.cc
@@ -689,6 +689,7 @@ static const struct default_options default_options_table[] =
     { OPT_LEVELS_3_PLUS, OPT_funswitch_loops, NULL, 1 },
     { OPT_LEVELS_3_PLUS, OPT_fvect_cost_model_, NULL, VECT_COST_MODEL_DYNAMIC },
     { OPT_LEVELS_3_PLUS, OPT_fversion_loops_for_strides, NULL, 1 },
+    { OPT_LEVELS_3_PLUS, OPT_ftrack_subreg_liveness, NULL, 1 },
 
     /* -O3 parameters.  */
     { OPT_LEVELS_3_PLUS, OPT__param_max_inline_insns_auto_, NULL, 30 },