Simon Peyton-Jones wrote:
| > GHC does some constant folding, but little by way of strength
| reduction, or using shifts instead of multiplication. It's pretty easy
| to add more: it's all done in a single module. Look at primOpRules in
| the module PrelRules.
| >
| > Patches welcome! But please also supply test-suite tests that check
| the correctness of the rules.
| >
|
| So... you mean it's source-level transformation rules? (Rather than
| wired into the compiler itself somewhere.)
No, constant folding is part of the compiler, I'm afraid, in the module
PrelRules.
Simon
_Constant_ folding is, but in GHC.Base there are rules like (unboxed)
multiplying by zero or one, or adding or subtracting zero, from an
unknown other (non-constant) value. I think shifts might be doable via
RULES... if you were willing to make one rule for each denominator 2, 4,
8 and so on, which rather depends on max. Int... (and that's not
Integers either, I guess)
Isaac
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