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From: joeo@sharp..westford.ccur.com (Joe Orost)
Newsgroups: comp.arch,ccc.eng
Subject: Re: bizarre instructions
Message-ID: <61756@masscomp.westford.ccur.com>
Date: 26 Feb 91 12:17:22 GMT
References: <9102220245.AA14853@ucbvax.Berkeley.EDU> <1991Feb25.134714.23523@linus.mitre.org> <10244@dog.ee.lbl.gov> <1991Feb25.203629.5059@linus.mitre.org> <10278@dog.ee.lbl.gov>
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Reply-To: joeo@tinton.ccur.com (Joe Orost)
Followup-To: comp.arch
Organization: Concurrent Computer Corporation, Tinton Falls, NJ
Lines: 48

In article <10278@dog.ee.lbl.gov> torek@elf.ee.lbl.gov (Chris Torek) writes:
>
>I have only a vague idea what `could not be done in the HLL' means.
>Did I use a construct that is not provided by the compiler?  Or is
>`assembler routines had to be called' the key phrase?  Do you mean
>`machine dependent instructions had to be emitted'?  Of course this is
>the case.  Do you mean `the rules for emitting the machine dependent
>instructions were not built into the compiler'?  This depends on what
>one means by `built in'.  Is the following sin() routine `built in'
>to the compiler?:
>
>	static __inline const double sin(double x) {
>		double result;
>		__asm("sin %1,%0" : "=f"(result) : "f"(x));
>		return result;
>	}
>
>I claim that if this appears in <math.h>, it *is* built-in to the
>compiler, despite the fact that the compiler reads these rules from an
>external file rather than having them embedded directly in its
>executable.

Not so fast.  Our C3Ada-68K compiler and our Fortran VII-3200 compiler has the 
transcendentals built-in.  This means much more than just compiling the 
calls inline.  Built-in means that:

	1. Constant evaluation is performed at compile time:
	   SIN(0.0) is replaced by 0.0, etc.
	2. Common subexpressions and loop invarient code motion is
	   performed on these operations at compile time:
	   SIN(A)   ...   SIN(A)  replaced by one call using a tempo.
	3. Special-case optimizations are performed:
	   A**0.5 -> SQRT(A)
	   A**1.0 -> A
	4. The compiler knows the argument profile for the routines.
	   In Fortran, SQRT(2) gets a warning and is converted to SQRT(2.0).
	4. The calls generate inline code.

				regards,
				joe

--

 Full-Name:  Joseph M. Orost
 Email:	     joeo@tinton.ccur.com
 Phone:      (908) 758-7284         Fax: (908) 758-7113
 US Mail:    MS 322; Concurrent Computer Corporation; 106 Apple St
             Tinton Falls, NJ 07724


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