From be342e86382616d1f71f3e750e35bbf889d5dd46 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Lindqvist?= <bjourne@gmail.com>
Date: Sun, 14 Jun 2015 02:13:31 +0200
Subject: [PATCH] compiler.cfg.ssa.destruction: refactors
 maybe/must-eliminate-copy into one try-eliminate-copy

---
 .../ssa/destruction/destruction-docs.factor   | 26 ++++++++------
 .../cfg/ssa/destruction/destruction.factor    | 34 +++++++------------
 2 files changed, 27 insertions(+), 33 deletions(-)

diff --git a/basis/compiler/cfg/ssa/destruction/destruction-docs.factor b/basis/compiler/cfg/ssa/destruction/destruction-docs.factor
index 1c10ca97ac..d4f21aebe0 100644
--- a/basis/compiler/cfg/ssa/destruction/destruction-docs.factor
+++ b/basis/compiler/cfg/ssa/destruction/destruction-docs.factor
@@ -1,27 +1,31 @@
 USING: compiler.cfg compiler.cfg.instructions
-compiler.cfg.ssa.destruction.private help.markup help.syntax ;
+compiler.cfg.ssa.destruction.private compiler.cfg.ssa.interference help.markup
+help.syntax kernel ;
 IN: compiler.cfg.ssa.destruction
 
 HELP: class-element-map
-{ $var-description "Maps leaders to equivalence class elements." } ;
+{ $var-description "Maps leaders to equivalence class elements which are sequences of " { $link vreg-info } " instances." } ;
 
 HELP: cleanup-cfg
 { $values { "cfg" cfg } }
 { $description "In this step, " { $link ##parallel-copy } " instructions are substituted with more concreete " { $link ##copy } " instructions. " { $link ##phi } " instructions are removed here." } ;
 
+HELP: coalesce-elements
+{ $values { "merged" "??" } { "follower" "vreg" } { "leader" "vreg" } }
+{ $description "Delete follower's class, and set leaders's class to merged." } ;
+
+HELP: coalesce-vregs
+{ $values { "merged" "??" } { "follower" "vreg" } { "leader" "vreg" } }
+{ $description "Sets 'leader' as the leader of 'follower'." } ;
+
 HELP: copies
 { $var-description "Sequence of copies (tuples of { vreg-dst vreg-src}) that maybe can be eliminated later." }
 { $see-also init-coalescing } ;
 
-HELP: maybe-eliminate-copy
-{ $values { "vreg1" "vreg" } { "vreg2" "vreg" } }
-{ $description "Eliminate a copy if possible." }
-{ $see-also must-eliminate-copy } ;
-
-HELP: must-eliminate-copy
-{ $values { "vreg1" "vreg" } { "vreg2" "vreg" } }
-{ $description "Eliminates a copy." }
-{ $see-also maybe-eliminate-copy } ;
+HELP: try-eliminate-copy
+{ $values { "follower" "vreg" } { "leader" "vreg" } { "must?" boolean } }
+{ $description "Tries to eliminate a vreg copy from 'leader' to 'follower'. If 'must?' is " { $link t } " then a " { $link vregs-shouldn't-interfere } " error is thrown if the vregs interfere." }
+{ $see-also vregs-interfere? } ;
 
 ARTICLE: "compiler.cfg.ssa.destruction" "SSA Destruction"
 "Because of the design of the register allocator, this pass has three peculiar properties."
diff --git a/basis/compiler/cfg/ssa/destruction/destruction.factor b/basis/compiler/cfg/ssa/destruction/destruction.factor
index d806f73771..c5ad460bdb 100644
--- a/basis/compiler/cfg/ssa/destruction/destruction.factor
+++ b/basis/compiler/cfg/ssa/destruction/destruction.factor
@@ -7,7 +7,7 @@ compiler.cfg.registers compiler.cfg.rpo compiler.cfg.ssa.cssa
 compiler.cfg.ssa.destruction.leaders
 compiler.cfg.ssa.interference
 compiler.cfg.ssa.interference.live-ranges compiler.cfg.utilities
-cpu.architecture kernel locals make namespaces sequences sets ;
+cpu.architecture kernel make namespaces sequences sets ;
 FROM: namespaces => set ;
 IN: compiler.cfg.ssa.destruction
 
@@ -15,7 +15,6 @@ SYMBOL: class-element-map
 
 <PRIVATE
 
-! Sequence of vreg pairs
 SYMBOL: copies
 
 : value-of ( vreg -- value )
@@ -30,11 +29,10 @@ SYMBOL: copies
     ] bi
     V{ } clone copies set ;
 
-: coalesce-elements ( merged vreg1 vreg2 -- )
-    ! delete leader1's class, and set leader2's class to merged.
+: coalesce-elements ( merged follower leader -- )
     class-element-map get [ delete-at ] [ set-at ] bi-curry bi* ;
 
-: coalesce-vregs ( merged leader1 leader2 -- )
+: coalesce-vregs ( merged follower leader -- )
     2dup swap leader-map get set-at coalesce-elements ;
 
 GENERIC: prepare-insn ( insn -- )
@@ -68,32 +66,24 @@ M: ##parallel-copy prepare-insn
 
 ERROR: vregs-shouldn't-interfere vreg1 vreg2 ;
 
-:: must-eliminate-copy ( vreg1 vreg2 -- )
-    vreg1 vreg2 = [
-        vreg1 vreg2 vregs-interfere?
-        [ vreg1 vreg2 vregs-shouldn't-interfere ]
-        [ vreg1 vreg2 coalesce-vregs ]
-        if
-    ] unless ;
+: try-eliminate-copy ( follower leader must? -- )
+    -rot leaders 2dup = [ 3drop ] [
+        2dup vregs-interfere? [
+            drop rot [ vregs-shouldn't-interfere ] [ 2drop ] if
+        ] [ -rot coalesce-vregs drop ] if
+    ] if ;
 
 M: ##tagged>integer prepare-insn
-    [ dst>> ] [ src>> ] bi leaders must-eliminate-copy ;
+    [ dst>> ] [ src>> ] bi t try-eliminate-copy ;
 
 M: ##phi prepare-insn
-    [ dst>> ] [ inputs>> values ] bi
-    [ leaders must-eliminate-copy ] with each ;
+    [ dst>> ] [ inputs>> values ] bi [ t try-eliminate-copy ] with each ;
 
 : prepare-coalescing ( cfg -- )
     init-coalescing [ [ prepare-insn ] each ] simple-analysis ;
 
-:: maybe-eliminate-copy ( vreg1 vreg2 -- )
-    vreg1 vreg2 = [
-        vreg1 vreg2 vregs-interfere?
-        [ drop ] [ vreg1 vreg2 coalesce-vregs ] if
-    ] unless ;
-
 : process-copies ( copies -- )
-    [ leaders maybe-eliminate-copy ] assoc-each ;
+    [ f try-eliminate-copy ] assoc-each ;
 
 : perform-coalescing ( cfg -- )
     prepare-coalescing copies get process-copies ;