compiler.cfg.*: the make-kill-block word is not needed

basis/compiler/cfg/builder/blocks/blocks-docs.factor

@@ -70,10 +70,6 @@ HELP: end-branch
 { $values { "block" basic-block } { "pair/f" "two-tuple" } }
 { $description "pair is { final-bb final-height }" } ;
 
-HELP: make-kill-block
-{ $values { "block" basic-block } }
-{ $description "Marks the block as a kill block." } ;
-
 HELP: set-basic-block
 { $values { "basic-block" basic-block } }
 { $description "Sets the given blocks as the current one by storing it in the basic-block dynamic variable. If it has any " { $slot "instructions" } " the current " { $link building } " is set to those." } ;

basis/compiler/cfg/builder/blocks/blocks-tests.factor

@@ -33,11 +33,6 @@ IN: compiler.cfg.builder.blocks.tests
     <basic-block> dup set-basic-block ##branch, end-basic-block
 ] unit-test
 
-! make-kill-block
-{ t } [
-    <basic-block> [ make-kill-block ] keep kill-block?>>
-] unit-test
-
 {
     { "succ" "succ" "succ" }
 } [

basis/compiler/cfg/builder/blocks/blocks.factor

@@ -22,14 +22,11 @@ IN: compiler.cfg.builder.blocks
     [ swap call ] keep
     ##branch, begin-basic-block ; inline
 
-: make-kill-block ( block -- )
-    t swap kill-block?<< ;
-
 : call-height ( #call -- n )
     [ out-d>> length ] [ in-d>> length ] bi - ;
 
 : emit-call-block ( word height block -- )
-    make-kill-block adjust-d ##call, ;
+    t swap kill-block?<< adjust-d ##call, ;
 
 : emit-trivial-call ( block word height -- block' )
     rot [ emit-call-block ] emit-trivial-block ;

basis/compiler/cfg/builder/builder.factor

@@ -37,7 +37,7 @@ GENERIC: emit-node ( block node -- block' )
     [ over [ emit-node ] [ drop ] if ] each ;
 
 : begin-word ( block -- block' )
-    dup make-kill-block
+    t >>kill-block?
     ##safepoint, ##prologue, ##branch,
     begin-basic-block ;
 
@@ -165,10 +165,8 @@ M: #shuffle emit-node ( block node -- block' )
 ! #return
 : end-word ( block -- block' )
     ##branch, begin-basic-block
-    dup make-kill-block
-    ##safepoint,
-    ##epilogue,
-    ##return, ;
+    t >>kill-block?
+    ##safepoint, ##epilogue, ##return, ;
 
 M: #return emit-node ( block node -- block' )
     drop end-word ;

basis/compiler/cfg/cfg-docs.factor

@@ -1,19 +1,20 @@
 USING: compiler.cfg.instructions compiler.cfg.rpo
-compiler.cfg.stack-frame compiler.tree help.markup help.syntax math
-namespaces sequences vectors words ;
+compiler.cfg.stack-frame compiler.tree help.markup help.syntax kernel
+math namespaces sequences vectors words ;
 IN: compiler.cfg
 
 HELP: basic-block
 { $class-description
-  "Factors representation of a basic block in the Call Flow Graph (CFG). A basic block is a sequence of instructions that always are executed sequentially and doesn't contain any branching. It has the following slots:"
+  "Factors representation of a basic block in the Call Flow Graph (CFG). A basic block is a sequence of instructions that always are executed sequentially and doesn't contain any internal branching. It has the following slots:"
   { $table
     { { $slot "number" } { "The blocks sequence number. Generated by calling " { $link number-blocks } ". " } }
     { { $slot "successors" } { "A " { $link vector } " of basic blocks that may be executed directly after this block. Most blocks only have one successor but a block that checks where an if-condition should branch to would have two for example." } }
     { { $slot "predecessors" } { "The opposite of successors -- a " { $link vector } " of basic blocks from which the execution may have arrived into this block." } }
     { { $slot "instructions" } { "A " { $link vector } " of " { $link insn } " tuples which form the instructions of the basic block." } }
-    { { $slot "kill-block?" } { "The first and the last block in a cfg and all blocks containing " { $link ##call } " instructions are kill blocks." } }
+    { { $slot "kill-block?" } { "The first and the last block in a cfg and all blocks containing " { $link ##call } " instructions are kill blocks. Kill blocks can't be optimized so they are omitted from certain optimization steps." } }
   }
-} ;
+}
+{ $notes "A basic-block is an " { $link identity-tuple } " becase it is used as a hash table key by the compiler." } ;
 
 HELP: <basic-block>
 { $values { "bb" basic-block } }