Frob numeric.c loop so that clang will auto-vectorize it too.
Experimentation shows that clang will auto-vectorize the critical multiplication loop if the termination condition is written "i2 < limit" rather than "i2 <= limit". This seems unbelievably stupid, but I've reproduced it on both clang 9.0.1 (RHEL8) and 11.0.3 (macOS Catalina). gcc doesn't care, so tweak the code to do it that way. Discussion: https://postgr.es/m/CAJ3gD9evtA_vBo+WMYMyT-u=keHX7-r8p2w7OSRfXf42LTwCZQ@mail.gmail.com
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@ -8191,7 +8191,6 @@ mul_var(const NumericVar *var1, const NumericVar *var2, NumericVar *result,
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int res_weight;
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int maxdigits;
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int *dig;
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int *dig_i1_2;
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int carry;
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int maxdig;
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int newdig;
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@ -8327,7 +8326,7 @@ mul_var(const NumericVar *var1, const NumericVar *var2, NumericVar *result,
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* Add the appropriate multiple of var2 into the accumulator.
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*
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* As above, digits of var2 can be ignored if they don't contribute,
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* so we only include digits for which i1+i2+2 <= res_ndigits - 1.
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* so we only include digits for which i1+i2+2 < res_ndigits.
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*
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* This inner loop is the performance bottleneck for multiplication,
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* so we want to keep it simple enough so that it can be
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@ -8336,11 +8335,14 @@ mul_var(const NumericVar *var1, const NumericVar *var2, NumericVar *result,
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* Since we aren't propagating carries in this loop, the order does
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* not matter.
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*/
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i = Min(var2ndigits - 1, res_ndigits - i1 - 3);
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dig_i1_2 = &dig[i1 + 2];
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for (i2 = 0; i2 <= i; i2++)
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{
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int i2limit = Min(var2ndigits, res_ndigits - i1 - 2);
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int *dig_i1_2 = &dig[i1 + 2];
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for (i2 = 0; i2 < i2limit; i2++)
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dig_i1_2[i2] += var1digit * var2digits[i2];
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}
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}
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/*
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* Now we do a final carry propagation pass to normalize the result, which
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