sv: support assignments within expressions #3920
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- Add support for assignments within expressions, e.g., `x[y++] = z;` or `x = (y *= 2) - 1;`. The logic is handled entirely within the parser by injecting statements into the current procedural block. - Add support for pre-increment/decrement statements, which are behaviorally equivalent to post-increment/decrement statements. - Fix non-standard attribute position used for post-increment/decrement statements.
frontends/verilog/verilog_parser.y
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| // The position 1 attr to avoid shift/reduce conflicts with the | ||
| // other productions. We reject attributes in that position. | ||
| if (!$1->empty()) | ||
| frontend_verilog_yyerror("Attributes are not allowed on this size of the lvalue in an inc_or_dec_expression!"); |
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As far as I can tell these attributes would be allowed by the standard, since attributes can be prefix to a statement and this is a self-standing statement, no?
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Good point! I'll pushing a fix for this shortly.
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| // create a pre/post-increment/decrement expression, and add the corresponding statement | ||
| static AstNode *addIncOrDecExpr(AstNode *lhs, dict<IdString, AstNode*> *attr, AST::AstNodeType op, YYLTYPE begin, YYLTYPE end, bool undo) | ||
| { |
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I think we want to recover the sizing information here, or do something other than the plus one minus one dance (maybe an assignment to a dummy wire?). Consider the following:
w = {1, r++};
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This is a great catch! I should have set the width of minus_one explicitly to prevent it from affecting the width of the expression. This logic seems simpler than the alternatives I considered: A) adding a temporary wire; or B) actually doing the increment afterwards. That said, my preference here likely comes from having done it the same way in sv2v.
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Other than the two comments I went through all of it and it looks good. |
x[y++] = z;orx = (y *= 2) - 1;. The logic is handled entirely within the parser by injecting statements into the current procedural block.I am not particularly attached to this implementation. I had initially anticipated adding a new AST node type and elaborating them in
simplify.cc, but sticking the statements into the current procedure ended up working quite naturally.Closes #3870.