compiler: add ##safepoint IR insn

basis/compiler/cfg/instructions/instructions.factor

@@ -84,6 +84,8 @@ INSN: ##epilogue ;
 
 INSN: ##return ;
 
+INSN: ##safepoint ;
+
 ! Dummy instruction that simply inhibits TCO
 INSN: ##no-tco ;
 

basis/compiler/cfg/scheduling/scheduling.factor

@@ -57,6 +57,7 @@ UNION: final-insn
 ##branch
 ##dispatch
 conditional-branch-insn
+##safepoint
 ##epilogue ##return
 ##callback-outputs ;
 

basis/compiler/codegen/codegen.factor

@@ -160,6 +160,7 @@ CODEGEN: ##inc-r %inc-r
 CODEGEN: ##call %call
 CODEGEN: ##jump %jump
 CODEGEN: ##return %return
+CODEGEN: ##safepoint %safepoint
 CODEGEN: ##slot %slot
 CODEGEN: ##slot-imm %slot-imm
 CODEGEN: ##set-slot %set-slot

basis/cpu/architecture/architecture.factor

@@ -495,6 +495,8 @@ HOOK: %call-gc cpu ( gc-map -- )
 HOOK: %prologue cpu ( n -- )
 HOOK: %epilogue cpu ( n -- )
 
+HOOK: %safepoint cpu ( -- )
+
 HOOK: test-instruction? cpu ( -- ? )
 
 M: object test-instruction? f ;

basis/cpu/x86/32/32.factor

@@ -218,6 +218,9 @@ M:: x86.32 stack-cleanup ( stack-size return abi -- n )
 M: x86.32 %cleanup ( n -- )
     [ ESP swap SUB ] unless-zero ;
 
+M: x86.32 %safepoint
+    0 EAX MOVABS rc-absolute rel-safepoint ;
+
 M: x86.32 dummy-stack-params? f ;
 
 M: x86.32 dummy-int-params? f ;

basis/cpu/x86/64/64.factor

@@ -130,6 +130,9 @@ M: x86.64 stack-cleanup 3drop 0 ;
 
 M: x86.64 %cleanup 0 assert= ;
 
+M: x86.64 %safepoint
+    0 [RIP+] EAX MOV rc-relative rel-safepoint ;
+
 M: x86.64 long-long-on-stack? f ;
 
 M: x86.64 float-on-stack? f ;