1) Customers who want their text-size to be as small as possible so they can shave $0.0015 off their BOM by using smaller ROM parts
2) Chip vendors who have 7 figure sales that will fall-through if they can't show a 0.7% higher Dhrystone MIPS (yes Dhrystone, the benchmark that was obsolete 20 years ago).
3) Managers who make buying decisions purely based on a set of their own pet benchmarks, with no regard to anything in this paper.
Damn right a compiler will take advantage of every optimization opportunity afforded by the standard. Good compilers will have ways of being much less aggressive about optimizations; I bet with gcc and clang each you have some -f flags that will disable certain optimizations (not to mention just good old -O0); I know most commercial compilers do.
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I would like to see some less-optimizable C standard catch on, so that there could be a mode common to multiple compilers that makes programmers happy. Unfortunately attempts to create such a dialect have failed to get off the ground.
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Part of this is because there is less of a consensus on what are optimizations* and "optimizations" than the author would believe.