Add ((id+/-e)+/-id) simplification rule #1268
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uxmal
reviewed
Jul 16, 2023
| binLeft.Left, binExp.Right), | ||
| binLeft.Right); | ||
| return (binExp, true); | ||
| } |
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Is this a safe transformation when taking unsigned or signed overflow into account? I refer to the regression suite, where several subjects have regressed.
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I think, (id + e) - id is always e. Given id=0xffffffff , e = 1, (0xffffffff + 1) = 0, (0 - 0xffffffff) = 1. But I need to do more detailed testing on mentioned samples. Maybe there are problems at other rules.
| @@ -17161,7 +17161,7 @@ byte fn0000EB48(Eq_n r0, Eq_n r1, ui32 r2, struct Eq_n * r3, Eq_n r4, Eq_n r5, s | |||
| if (r2_n <= r5_n) | |||
| { | |||
| r2_n.u0 = r5_n.u0 + 1; | |||
| if (r5_n.u0 + 1 < r5_n) | |||
| if (false) | |||
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This looks like a saturated add: first check for unsigned overflow, and if so, force the value to 0xFFFFFFFF. This regression cannot be allowed.
| @@ -193,7 +193,7 @@ int32 fn0000275C(struct Eq_n * a0, struct Eq_n * a5, struct Eq_n & a0Out) | |||
| a5->ptrFFFFFAD0 = a0; | |||
| struct Eq_n * d0_n = a0; | |||
| struct Eq_n * d1_n = (char *) &a0->t0004 + 4; | |||
| if (&a0->dw0FF8 > a0) | |||
| if (true) | |||
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This is also a regression that needs addressing.
It's unsafe to simplify 'cond(e)'. This operation actually requires flags of expression, not expression itseft. So ConditionCodeEliminator should do its work before. For instance we have cond(x - y) where x = y + 1 and can't simplify it to cond((y + 1) - y) => cond(1). 'y + 1 > y' can be used as test for overflow.
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