Re: Languages that give "hints" to the compiler

Our esteemed moderator wrote:
>[The original FORTRAN compiler had a FREQUENCY statement that let you give
>a hint to the compiler how many times a DO loop would run or which was the
>most likely branch of an IF. It disappeared in Fortran II. Legend says
>that the final nail in its coffin was when someone found that it was
>implemented backwards and nobody had noticed. -John]


I believe it was Lois Haibt at Yorktown who 10 years ago told me the story
in response to my mentioning the branch frequency directive in the Yale
Bulldog Compiler. As I recall, she said she'd released the 7090? code
generator--it used the FREQ statement for some different treatment of the
index register--and then went on vacation. While she was out, someone
upstream from her code reversed the sense. She found it herself a year
and a half later.


This was in the days of suspicion of compilers and hacking of object code.
No one ever caught it; she never got a bug report.


-- Josh Fisher // HP Labs Cambridge Research
--

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