Re:On the Madness of Optimizing Compilers
by mpweiher on Tuesday March 08, 2016 @04:12AM
(#11244249)
I blame:
(a) free compilers
(b) the C standard
Crazy talk, surely! Let me explain: each of these is a Good Thing™, but together they have put us in our current predicament. It used to be that compilers were reasonably expensive products, so as a vendor you had a clear incentive not to piss off your customers. In addition (in the very olden days), there as no C standard so the definition of "correct" was very customer-based: if customer code compiled well, you were doing a good job, if not, you would probably suffer.
With compilers becoming free, the incentive structure changed, customers now matter very little. Instead, you get ahead in that pecking order by improving some SPEC benchmark by 0.2%. At the same time, the C standard, which was worded very inclusively so even compilers for odd architectures could be ANSI/ISO compliant, was used as a substitute for "my customers' code works", and people started to say silly things like "if you have undefined behaviour, demons can fly out your nose".
Well: I had a pre-ANSI compiler. ALL its behaviour was "undefined". And yet it took fewer liberties with the code than many of today's compilers do. Because the creators (a) were reasonable people and (b) had real customers.
(a) free compilers
(b) the C standard
Crazy talk, surely! Let me explain: each of these is a Good Thing™, but together they have put us in our current predicament. It used to be that compilers were reasonably expensive products, so as a vendor you had a clear incentive not to piss off your customers. In addition (in the very olden days), there as no C standard so the definition of "correct" was very customer-based: if customer code compiled well, you were doing a good job, if not, you would probably suffer.
With compilers becoming free, the incentive structure changed, customers now matter very little. Instead, you get ahead in that pecking order by improving some SPEC benchmark by 0.2%. At the same time, the C standard, which was worded very inclusively so even compilers for odd architectures could be ANSI/ISO compliant, was used as a substitute for "my customers' code works", and people started to say silly things like "if you have undefined behaviour, demons can fly out your nose".
Well: I had a pre-ANSI compiler. ALL its behaviour was "undefined". And yet it took fewer liberties with the code than many of today's compilers do. Because the creators (a) were reasonable people and (b) had real customers.