0005595: Missed constant propagation

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0005595

OCaml

OCaml backend (code generation)

public

2012-04-17 16:00

2012-04-19 17:20

Reporter

frisch

Assigned To

frisch

Priority

normal

Severity

minor

Reproducibility

have not tried

Status

resolved

Resolution

fixed

Platform

OS Version

Product Version

Target Version

Fixed in Version

Summary

0005595: Missed constant propagation

Description

The following patch:

===================================================================
--- asmcomp/cmmgen.ml (revision 12366)
+++ asmcomp/cmmgen.ml (working copy)
@@ -78,7 +78,10 @@
           (Nativeint.add (Nativeint.shift_left (Nativeint.of_int n) 1) 1n)

let add_const c n =
- if n = 0 then c else Cop(Caddi, [c; Cconst_int n])
+ if n = 0 then c
+ else match c with
+ | Cconst_int x when no_overflow_add x n -> Cconst_int (x + n)
+ | c -> Cop(Caddi, [c; Cconst_int n])

let incr_int = function
     Cconst_int n when n < max_int -> Cconst_int(n+1)
===================================================================

improves code generation, for instance for the following example:

===================================================================
let () =
  let tr = Bigarray.(Array2.of_array int fortran_layout [| [|1|] |]) in
  for i = 1 to 1000000000 do ignore tr.{1, 1} done
===================================================================

On my machine, runtime goes from 1.77s to 1.46s.

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Notes
(0007373) frisch (developer) 2012-04-18 09:17	Commit 12368.

Issue History
Date Modified	Username	Field	Change
2012-04-17 16:00	frisch	New Issue
2012-04-18 09:07	frisch	Assigned To	=> frisch
2012-04-18 09:07	frisch	Status	new => assigned
2012-04-18 09:17	frisch	Note Added: 0007373
2012-04-18 09:17	frisch	Status	assigned => resolved
2012-04-18 09:17	frisch	Resolution	open => fixed