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Always mask LSB in V3Merge Cond when mergin AstAnd

This commit is contained in:
Geza Lore 2020-06-06 00:16:16 +01:00
parent ff41701ddc
commit 4a404bd92e
1 changed files with 9 additions and 10 deletions
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19
src/V3MergeCond.cpp
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@ -153,17 +153,16 @@ private:
return NULL; return NULL;
} }
// Apply (_ & 1'b1), iff node is wider than 1 bit. This is necessary // Apply (_ & 1'b1). This is necessary because this pass is after V3Clean,
// because this pass is after V3Clean, and sometimes we have an AstAnd with // and sometimes we have an AstAnd with a 1-bit condition on one side, but
// a 1-bit condition on one side, but a more than 1-bit value on the other // a more than 1-bit value on the other side, so we need to keep only the
// side, so we need to keep only the LSB. // LSB. Ideally we would only do this iff the node is known not to be 1-bit
// wide, but working that out here is a bit difficult. As this masking is
// rarely required (only when trying to merge a "cond & value" with an
// earlier ternary), we will just always mask it for safety.
AstNode* maskLsb(AstNode* nodep) { AstNode* maskLsb(AstNode* nodep) {
if (nodep->width1()) { AstNode* const maskp = new AstConst(nodep->fileline(), AstConst::LogicTrue());
return nodep; return new AstAnd(nodep->fileline(), nodep, maskp);
} else {
AstNode* const maskp = new AstConst(nodep->fileline(), AstConst::LogicTrue());
return new AstAnd(nodep->fileline(), nodep, maskp);
}
} }
// Fold the RHS expression assuming the given condition state. Unlink bits // Fold the RHS expression assuming the given condition state. Unlink bits