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cmp: add a comment that explains the purpose of OPTIMIZE-CXX-DATA

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Daniel Kochmański 2023-11-05 11:03:07 +01:00
parent 1b8d1041dd
commit edfaec9a6b
1 changed files with 16 additions and 0 deletions
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16
src/cmp/cmpbackend-cxx/cmppass2-data.lsp
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@ -345,6 +345,22 @@
(and errorp
(cmperr "Unable to find object ~s." object))))
;;; The vector *REFERENCED-OBJECTS* contains all referenced objects collected in
;;; the first pass. The function OPTIMIZE-CXX-DATA is responsible for inlining
;;; them when possible, and putting them in a temporary/permanent data segments
;;; otherwise. Objects in data segment require an explicit initialization when
;;; the the module is loaded. The following inline strategies are tried:
;;;
;;; - using a symbol from the core :: ECL_SYM(\"*BREAK-ON-SIGNALS*\",27)
;;; - using a cvalue inline value :: cl_core.single_float_zero, FLT_MAX
;;; - using a static constructor :: ecl_def_ct_single_float -> _ecl_static_7
;;; - coercing an immediate value :: ecl_make_fixnum(42)
;;;
;;; Otherwise the object is put in VV or VVtemp vector, and is created when the
;;; module is loaded. Then the code refers to such objects as VV[13].
;;;
;;; TODO we could further optimize immediate values by duplicating some entries
;;; depending on the expected rep-type, to avoid unnecessary coercions.
(defun optimize-cxx-data (objects)
(flet ((optimize-vv (object)
(let ((value (vv-value object)))