core: Add IS_CT_CONSTANT() #17273
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core: Add IS_CT_CONSTANT() #17273
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maribu
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State: WIP
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I added a WIP because I haven't tested this yet for the motivating example stated (for using pin / port as immediate value in AVR assembly when the GPIO is a compile time constant). |
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benpicco
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CI: ready for build
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still WIP? |
maribu
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State: WIP
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No longer, I found a new user for it :) |
benpicco
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Dec 14, 2021
| { | ||
| /* These test might fail on non-GCC-non-clang compilers. We don't support | ||
| * any of those (yet), but this test might need adaption in the future */ | ||
| int actual_constant = (int)(42 * 1337 / 3.14159); |
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Suggested change
| int actual_constant = (int)(42 * 1337 / 3.14159); | |
| unsigned actual_constant = (unsigned)(42 * 1337 / 3.14159); |
to make MSP430 happy
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That was not enough to make GCC 11.2 for the AVR happy, I changed the computation a bit to not overflow. In addition, I moved this into at static inline function to make it a bit less trivial, so that we have a decent base-line on what we expect from compilers to detect as suitable for constant-folding.
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aabadie
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Jan 5, 2022
This adds a simple macro to check (at C level) whether a given
expression is proven to be compile time constant and suitable for
constant folding. This allows writing code like this:
```C
int gpio_read(gpio_t pin) {
if (IS_CT_CONSTANT(pin)) {
/* this implementation should even be able to use the port and
* pin number as immediate in inline assembly */
}
else {
/* less efficient implementation that cannot use port and pin
* number as immediate in inline assembly */
}
}
```
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aabadie
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benpicco
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Jan 7, 2022
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Process: needs >1 ACK
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Contribution description
This adds a simple macro to check (at C level) whether a given expression is proven to be compile time constant and suitable for constant folding. This allows writing code like this:
Testing procedure
A unit test was provided that should do the trick.
Issues/PRs references
None