Plus the experience from all from us that had access to early C compilers on CP/M and home micros.
IBM already had a LLVM like toolchain for their RISC research with PL.8 and respective OS.
Only later did they switch to UNIX due to the market they were after.
Surviving mainframes are still writen on their system languages.
As for Fran Allen point of view:
"Oh, it was quite a while ago. I kind of stopped when C came out. That was a big blow. We were making so much good progress on optimizations and transformations. We were getting rid of just one nice problem after another. When C came out, at one of the SIGPLAN compiler conferences, there was a debate between Steve Johnson from Bell Labs, who was supporting C, and one of our people, Bill Harrison, who was working on a project that I had at that time supporting automatic optimization...The nubbin of the debate was Steve's defense of not having to build optimizers anymore because the programmer would take care of it. That it was really a programmer's issue.... Seibel: Do you think C is a reasonable language if they had restricted its use to operating-system kernels? Allen: Oh, yeah. That would have been fine. And, in fact, you need to have something like that, something where experts can really fine-tune without big bottlenecks because those are key problems to solve. By 1960, we had a long list of amazing languages: Lisp, APL, Fortran, COBOL, Algol 60. These are higher-level than C. We have seriously regressed, since C developed. C has destroyed our ability to advance the state of the art in automatic optimization, automatic parallelization, automatic mapping of a high-level language to the machine. This is one of the reasons compilers are ... basically not taught much anymore in the colleges and universities."
-- Fran Allen interview, Excerpted from: Peter Seibel. Coders at Work: Reflections on the Craft of Programming
Why do you keep sidestepping logical arguments with irrelevant quotes? Correct programs don't contain UB (even the fast ones), so UB is not what makes C fast.
Not checking for UB (aka invalid configurations) at runtime is what makes C (and any other language) fast - or more precisely, it's what allows compilers to emit efficient code.
Some languages / compilers rule out UB statically through the type system or other means, but that comes with tradeoffs that might, or might not, be worth making in your domain.
Because C guys keep spreading the false arguments that C was some kind of language sent by god to solve all performance issues, while we in the trenches when the language sprung into existence know it wasn't never the case.
Not to mention the fact that other programming languages, on the mainframe and workstation space, were already starting to collect the benefits of whole program optimizers.
Plus the experience from all from us that had access to early C compilers on CP/M and home micros.
IBM already had a LLVM like toolchain for their RISC research with PL.8 and respective OS.
Only later did they switch to UNIX due to the market they were after.
Surviving mainframes are still writen on their system languages.
As for Fran Allen point of view:
"Oh, it was quite a while ago. I kind of stopped when C came out. That was a big blow. We were making so much good progress on optimizations and transformations. We were getting rid of just one nice problem after another. When C came out, at one of the SIGPLAN compiler conferences, there was a debate between Steve Johnson from Bell Labs, who was supporting C, and one of our people, Bill Harrison, who was working on a project that I had at that time supporting automatic optimization...The nubbin of the debate was Steve's defense of not having to build optimizers anymore because the programmer would take care of it. That it was really a programmer's issue.... Seibel: Do you think C is a reasonable language if they had restricted its use to operating-system kernels? Allen: Oh, yeah. That would have been fine. And, in fact, you need to have something like that, something where experts can really fine-tune without big bottlenecks because those are key problems to solve. By 1960, we had a long list of amazing languages: Lisp, APL, Fortran, COBOL, Algol 60. These are higher-level than C. We have seriously regressed, since C developed. C has destroyed our ability to advance the state of the art in automatic optimization, automatic parallelization, automatic mapping of a high-level language to the machine. This is one of the reasons compilers are ... basically not taught much anymore in the colleges and universities."
-- Fran Allen interview, Excerpted from: Peter Seibel. Coders at Work: Reflections on the Craft of Programming