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The OpenBSD project used to verify gcc (back when it was at 4.2 or so) as compiler for their O/S. Don't know if they still do; I'd imagine it's a lot of effort,

The OpenBSD project used to verify gcc (back when it was at 4.2 or so) as compiler for their O/S. Don't know if they still do; I'd imagine it's a lot of effort, and both clang and gcc have churned out yearly releases with ever-growing complexity since. C was once supposed to be a simple language closer to a portable macro assembler than a high-level language, and one for which writing a compiler is relatively straightforward and takes no longer than a year. This went out of the window with clang, and with gcc (and glibc!) being based on C++. Though of course optimizing out-of-order execution on modern CPUs is much more complex than your olde microcontroller-like CPU.

jabl 6y ago
> C was once supposed to be a simple language closer to a portable macro assembler than a high-level language, That might have been K&R's original intention, but that went out the window pretty early on when optimizing compilers arrived on the scene. And eventually when the ANSI spec was written, it was explicitly written to allow all kinds of optimizations (the "as-if" rule).
- gwd 6y ago
  > And eventually when the ANSI spec was written, it was explicitly written to allow all kinds of optimizations (the "as-if" rule). The ironic thing about that is that when they wrote C89, they said they were trying to standardize existing practice. I don't think they had any idea that they were effectively declaring 90% of all programs buggy.
  - jfkebwjsbx 6y ago
    And then retroactively declare that code broken and not conforming. Good times!
    - jabl 6y ago
      In defense of whoever was involved in the C89 process, I think they had an impossible task. At the same time they wanted to standardize the "portable macro-assembler" as well as allowing optimizations. With such constraints they could not but fail. With hindsight, maybe K&R should have consulted with PL experts and researchers and designed a "proper" language with a better emphasis on soundness and safety. I'm not saying they could have invented something like Rust back in the 1970'ies, but even then the state of the art was far ahead of K&R C.
  - kps 6y ago
    > I don't think they had any idea that they were effectively declaring 90% of all programs buggy. I agree. During the standardization process, there was a proposal (‘noalias’) that dmr described as “a license for the compiler to undertake aggressive optimizations that are completely legal by the committee's rules, but make hash of apparently safe programs”, and, that “[i]t negates every brave promise X3J11 ever made about codifying existing practices, preserving the existing body of code, and keeping (dare I say it?) ‘the spirit of C.’”¹ If he or anyone else at the time had realized that ‘undefined behaviour’ would turn out to do the same, there response would have been the same: “[it] must go. This is non-negotiable.” ¹ https://www.lysator.liu.se/c/dmr-on-noalias.html https://www.lysator.liu.se/c/dmr-on-noalias.html
Quekid5 6y ago
> C was once supposed to be a simple language closer to a portable macro assembler than a high-level language, and one for which writing a compiler is relatively straightforward and takes no longer than a year. Do you have a source for this claim? AFAIU the history of C, it was invented for entirely pragmatic reasons. > This went out of the window with clang, and with gcc (and glibc!) being based on C++. This is nonsensical, whichever way one interprets "being based on C++". The GCC and Clang compilers conform to the standard whichever version of C or C++ you ask them compile. (Anything else is a bug and should be reported. They may accept a few non-conforming programs, but that's allowable under either implementation-defined behavior or undefined behavior. Remember that UB can include 'doing what the programmer expects'.)
- GoblinSlayer 6y ago
  That entirely pragmatic reason was to be assembler with curly braces. See memory capacity of PDP-7 and think what you can reasonably compile with those resources. Fun fact: if you don't specify variable's type, modern C compiler assumes int, this is how the first C compiler worked, you don't need types in assembler, the register type (machine word) is almost the only type you deal with. Implicit function declaration is an assembler feature too.
  - tannhaeuser 6y ago
    That's also how tcc (simplistic and functional modern one-pass C compiler) works I guess.
  - nineteen999 6y ago
    First C compiler ran on the PDP-11, rather than the PDP-7 didn't it? Not that it makes a huge different to your point.

jabl 6y ago

> C was once supposed to be a simple language closer to a portable macro assembler than a high-level language, That might have been K&R's original intention, but that went out the window pretty early on when optimizing compilers arrived on the scene. And eventually when the ANSI spec was written, it was explicitly written to allow all kinds of optimizations (the "as-if" rule).

gwd 6y ago
> And eventually when the ANSI spec was written, it was explicitly written to allow all kinds of optimizations (the "as-if" rule). The ironic thing about that is that when they wrote C89, they said they were trying to standardize existing practice. I don't think they had any idea that they were effectively declaring 90% of all programs buggy.
- jfkebwjsbx 6y ago
  And then retroactively declare that code broken and not conforming. Good times!
  - jabl 6y ago
    In defense of whoever was involved in the C89 process, I think they had an impossible task. At the same time they wanted to standardize the "portable macro-assembler" as well as allowing optimizations. With such constraints they could not but fail. With hindsight, maybe K&R should have consulted with PL experts and researchers and designed a "proper" language with a better emphasis on soundness and safety. I'm not saying they could have invented something like Rust back in the 1970'ies, but even then the state of the art was far ahead of K&R C.
- kps 6y ago
  > I don't think they had any idea that they were effectively declaring 90% of all programs buggy. I agree. During the standardization process, there was a proposal (‘noalias’) that dmr described as “a license for the compiler to undertake aggressive optimizations that are completely legal by the committee's rules, but make hash of apparently safe programs”, and, that “[i]t negates every brave promise X3J11 ever made about codifying existing practices, preserving the existing body of code, and keeping (dare I say it?) ‘the spirit of C.’”¹ If he or anyone else at the time had realized that ‘undefined behaviour’ would turn out to do the same, there response would have been the same: “[it] must go. This is non-negotiable.” ¹ https://www.lysator.liu.se/c/dmr-on-noalias.html https://www.lysator.liu.se/c/dmr-on-noalias.html

Quekid5 6y ago

> C was once supposed to be a simple language closer to a portable macro assembler than a high-level language, and one for which writing a compiler is relatively straightforward and takes no longer than a year. Do you have a source for this claim? AFAIU the history of C, it was invented for entirely pragmatic reasons. > This went out of the window with clang, and with gcc (and glibc!) being based on C++. This is nonsensical, whichever way one interprets "being based on C++". The GCC and Clang compilers conform to the standard whichever version of C or C++ you ask them compile. (Anything else is a bug and should be reported. They may accept a few non-conforming programs, but that's allowable under either implementation-defined behavior or undefined behavior. Remember that UB can include 'doing what the programmer expects'.)

GoblinSlayer 6y ago
That entirely pragmatic reason was to be assembler with curly braces. See memory capacity of PDP-7 and think what you can reasonably compile with those resources. Fun fact: if you don't specify variable's type, modern C compiler assumes int, this is how the first C compiler worked, you don't need types in assembler, the register type (machine word) is almost the only type you deal with. Implicit function declaration is an assembler feature too.
- tannhaeuser 6y ago
  That's also how tcc (simplistic and functional modern one-pass C compiler) works I guess.
- nineteen999 6y ago
  First C compiler ran on the PDP-11, rather than the PDP-7 didn't it? Not that it makes a huge different to your point.