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Consider children of AstConcat in V3InstrCount 

Previously V3InstrCount used to completely ignore an AstConcat,
including its children (see the rational in the comment). The problem is
the operands can be huge and expensive compound expressions (especially
since DFG), and not just a simple variable reference. This fix gains
some MT speed improvement.
This commit is contained in:
Geza Lore 2023-10-21 14:48:20 +01:00
parent afaa02709c
commit 1075b006b5
1 changed files with 5 additions and 6 deletions
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11
src/V3InstrCount.cpp
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@ -146,11 +146,9 @@ private:
} }
void visit(AstConcat* nodep) override { void visit(AstConcat* nodep) override {
if (m_ignoreRemaining) return; if (m_ignoreRemaining) return;
// Nop. // Ignore the cost of the concat node itself. The problem with
// // counting concat is that when we have many things concatted
// Ignore concat. The problem with counting concat is that when we // together, it's not a single operation, but this:
// have many things concatted together, it's not a single
// operation, but this:
// //
// concat(a, concat(b, concat(c, concat(d, ... )))) // concat(a, concat(b, concat(c, concat(d, ... ))))
// //
@ -162,7 +160,8 @@ private:
// cost is linear with the size of the data. We don't need to count // cost is linear with the size of the data. We don't need to count
// the concat at all to reflect a linear cost; it's already there // the concat at all to reflect a linear cost; it's already there
// in the width of the destination (which we count) and the sum of // in the width of the destination (which we count) and the sum of
// the widths of the operands (ignored here). // the cost of the operands.
iterateChildrenConst(nodep);
markCost(nodep); markCost(nodep);
} }
void visit(AstNodeIf* nodep) override { void visit(AstNodeIf* nodep) override {