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Optimize true/false conditions when coding if-statements
We already had some code which "optimized" some if-statements
with one or two conditions, where one or both were constant equal
to `true` or `false`. We skipped branches whose condition was
always `false`. However, we did not use the `IntrIgnoring` mechanism
for that. Thus, such code would still trigger warnings if it contained
undefined globals, e.g.
gap> f:=function() if false then undefined_global(); fi; end;;
Syntax warning: Unbound global variable
f:=function() if false then undefined_global(); fi; end;;
^
This can be viewed as a feature, or as a bug, depending on view point.
A reason to consider it a "bug" (or at least an undesirable feature)
is when using global constants to only conditionally execute code, such
as this:
if IsHPCGAP then
UNLOCK(lock);
fi;
This code is optimized away in regular GAP, but still triggers a warning
during parsing.
With this commit, we change how we deal with true/false conditions in
if-statements, by making use of the `IntrIgnoring` mechanism. This avoids
the warnings about globals in the examples above. It also has the side
effect of being "better" at optimizing away branches of an if-statement
which can never be executed.- Loading branch information
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,133 @@ | ||
| # | ||
| # Test the GAP function coder | ||
| # | ||
| gap> START_TEST("coding.tst"); | ||
|
|
||
| # | ||
| # Test coding of if-statements in which some conditions are true or false | ||
| # | ||
| # | ||
|
|
||
| # test if-statements with single branch | ||
| gap> f:=function(x) if x then return 1; fi; end;; Display(f); | ||
| function ( x ) | ||
| if x then | ||
| return 1; | ||
| fi; | ||
| return; | ||
| end | ||
| gap> f:=function(x) if true then return 1; fi; end;; Display(f); | ||
| function ( x ) | ||
| return 1; | ||
| end | ||
| gap> f:=function(x) if false then return 1; fi; end;; Display(f); | ||
| function ( x ) | ||
| ; | ||
| return; | ||
| end | ||
|
|
||
| # test if-statements with two branches (note that 'else' is equivalent to 'elif true'), | ||
| # first condition is neither true nor false | ||
| gap> f:=function(x) if x then return 1; else return 2; fi; end;; Display(f); | ||
| function ( x ) | ||
| if x then | ||
| return 1; | ||
| else | ||
| return 2; | ||
| fi; | ||
| return; | ||
| end | ||
| gap> f:=function(x) if x then return 1; elif x then return 2; fi; end;; Display(f); | ||
| function ( x ) | ||
| if x then | ||
| return 1; | ||
| elif x then | ||
| return 2; | ||
| fi; | ||
| return; | ||
| end | ||
| gap> f:=function(x) if x then return 1; elif false then return 2; fi; end;; Display(f); | ||
| function ( x ) | ||
| if x then | ||
| return 1; | ||
| fi; | ||
| return; | ||
| end | ||
|
|
||
| # test if-statements with two branches (note that 'else' is equivalent to 'elif true'), | ||
| # first condition is true | ||
| gap> f:=function(x) if true then return 1; else return 2; fi; end;; Display(f); | ||
| function ( x ) | ||
| return 1; | ||
| end | ||
| gap> f:=function(x) if true then return 1; elif x then return 2; fi; end;; Display(f); | ||
| function ( x ) | ||
| return 1; | ||
| end | ||
| gap> f:=function(x) if true then return 1; elif false then return 2; fi; end;; Display(f); | ||
| function ( x ) | ||
| return 1; | ||
| end | ||
|
|
||
| # test if-statements with two branches (note that 'else' is equivalent to 'elif true'), | ||
| # first condition is false | ||
| gap> f:=function(x) if false then return 1; else return 2; fi; end;; Display(f); | ||
| function ( x ) | ||
| return 2; | ||
| end | ||
| gap> f:=function(x) if false then return 1; elif x then return 2; fi; end;; Display(f); | ||
| function ( x ) | ||
| if x then | ||
| return 2; | ||
| fi; | ||
| return; | ||
| end | ||
| gap> f:=function(x) if false then return 1; elif false then return 2; fi; end;; Display(f); | ||
| function ( x ) | ||
| ; | ||
| return; | ||
| end | ||
|
|
||
| # test some if-statements with three branches | ||
| gap> f:=function(x) if true then return 1; elif true then return 2; else return 3; fi; end;; Display(f); | ||
| function ( x ) | ||
| return 1; | ||
| end | ||
| gap> f:=function(x) if true then return 1; elif x then return 2; else return 3; fi; end;; Display(f); | ||
| function ( x ) | ||
| return 1; | ||
| end | ||
| gap> f:=function(x) if x then return 1; elif true then return 2; else return 3; fi; end;; Display(f); | ||
| function ( x ) | ||
| if x then | ||
| return 1; | ||
| else | ||
| return 2; | ||
| fi; | ||
| return; | ||
| end | ||
| gap> f:=function(x) if x then return 1; elif false then return 2; else return 3; fi; end;; Display(f); | ||
| function ( x ) | ||
| if x then | ||
| return 1; | ||
| else | ||
| return 3; | ||
| fi; | ||
| return; | ||
| end | ||
| gap> f:=function(x) if false then return 1; elif true then return 2; else return 3; fi; end;; Display(f); | ||
| function ( x ) | ||
| return 2; | ||
| end | ||
| gap> f:=function(x) if false then return 1; elif x then return 2; else return 3; fi; end;; Display(f); | ||
| function ( x ) | ||
| if x then | ||
| return 2; | ||
| else | ||
| return 3; | ||
| fi; | ||
| return; | ||
| end | ||
|
|
||
| # | ||
| gap> STOP_TEST("coding.tst", 1); |
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