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Support more complex combinational assignments in DFG. (#6205)

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Previously DFG was limited to having a Sel, or an ArraySel potentially
under a Concat on the LHS of combinational assignments. Other forms or
combinations were not representable in the graph.

This adds support for arbitrary combinations of the above by
combining DfgSplicePacked and DfgSpliceArray vertices introduced in
 #6176. In particular, Sel(ArraySel(VarRef,_),_) enables a lot more code
to be represented in DFG.
This commit is contained in:
Geza Lore
2025-07-21 12:33:12 -04:00
committed by GitHub
parent 98b8d43a4a
commit a8dca71ed0
13 changed files with 658 additions and 356 deletions
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src/V3DfgDfgToAst.cpp
+47 -56
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@@ -188,65 +188,57 @@ class DfgToAstVisitor final : DfgVisitor {
return resultp;
}
void addResultEquation(const DfgVertexVar* vtxp, FileLine* flp, AstNodeExpr* lhsp,
AstNodeExpr* rhsp) {
AstAssignW* const assignp = new AstAssignW{flp, lhsp, rhsp};
if VL_CONSTEXPR_CXX17 (T_Scoped) {
// Add it to the scope holding the target variable
getCombActive(vtxp->varScopep()->scopep())->addStmtsp(assignp);
} else {
// Add it to the parend module of the DfgGraph
m_modp->addStmtsp(assignp);
void convertDriver(AstScope* scopep, FileLine* flp, AstNodeExpr* lhsp, DfgVertex* driverp) {
if (!driverp->is<DfgVertexSplice>()) {
// Base case: assign vertex to current lhs
AstNodeExpr* const rhsp = convertDfgVertexToAstNodeExpr(driverp);
AstAssignW* const assignp = new AstAssignW{flp, lhsp, rhsp};
lhsp->foreach([flp](AstNode* nodep) { nodep->fileline(flp); });
if VL_CONSTEXPR_CXX17 (T_Scoped) {
// Add it to the scope holding the target variable
getCombActive(scopep)->addStmtsp(assignp);
} else {
// Add it to the parend module of the DfgGraph
m_modp->addStmtsp(assignp);
}
++m_ctx.m_resultEquations;
return;
}
++m_ctx.m_resultEquations;
}
void convertPackedDriver(const DfgVarPacked* dfgVarp) {
if (DfgSplicePacked* const splicep = dfgVarp->srcp()->cast<DfgSplicePacked>()) {
// Variable is driven partially. Render each driver as a separate assignment.
splicep->forEachSourceEdge([&](const DfgEdge& edge, size_t idx) {
UASSERT_OBJ(edge.sourcep(), dfgVarp, "Should have removed undriven sources");
// Render the rhs expression
AstNodeExpr* const rhsp = convertDfgVertexToAstNodeExpr(edge.sourcep());
// Create select LValue
FileLine* const flp = splicep->driverFileLine(idx);
AstVarRef* const refp = new AstVarRef{flp, getNode(dfgVarp), VAccess::WRITE};
AstConst* const lsbp = new AstConst{flp, splicep->driverLsb(idx)};
if (DfgSplicePacked* const sPackedp = driverp->cast<DfgSplicePacked>()) {
// Partial assignment of packed value
sPackedp->forEachSourceEdge([&](const DfgEdge& edge, size_t i) {
UASSERT_OBJ(edge.sourcep(), sPackedp, "Should have removed undriven sources");
// Create Sel
FileLine* const dflp = sPackedp->driverFileLine(i);
AstConst* const lsbp = new AstConst{dflp, sPackedp->driverLsb(i)};
const int width = static_cast<int>(edge.sourcep()->width());
AstSel* const lhsp = new AstSel{flp, refp, lsbp, width};
// Add assignment of the value to the selected bits
addResultEquation(dfgVarp, flp, lhsp, rhsp);
AstSel* const nLhsp = new AstSel{dflp, lhsp->cloneTreePure(false), lsbp, width};
// Convert source
convertDriver(scopep, dflp, nLhsp, edge.sourcep());
// Delete Sel if not consumed
if (!nLhsp->backp()) VL_DO_DANGLING(nLhsp->deleteTree(), nLhsp);
});
return;
}
// Whole variable is driven. Render driver and assign directly to whole variable.
FileLine* const flp
= dfgVarp->driverFileLine() ? dfgVarp->driverFileLine() : dfgVarp->fileline();
AstVarRef* const lhsp = new AstVarRef{flp, getNode(dfgVarp), VAccess::WRITE};
AstNodeExpr* const rhsp = convertDfgVertexToAstNodeExpr(dfgVarp->srcp());
addResultEquation(dfgVarp, flp, lhsp, rhsp);
}
void convertArrayDiver(const DfgVarArray* dfgVarp) {
if (DfgSpliceArray* const splicep = dfgVarp->srcp()->cast<DfgSpliceArray>()) {
// Variable is driven partially. Assign from parts of the canonical var.
splicep->forEachSourceEdge([&](const DfgEdge& edge, size_t idx) {
UASSERT_OBJ(edge.sourcep(), dfgVarp, "Should have removed undriven sources");
// Render the rhs expression
AstNodeExpr* const rhsp = convertDfgVertexToAstNodeExpr(edge.sourcep());
// Create select LValue
FileLine* const flp = splicep->driverFileLine(idx);
AstVarRef* const refp = new AstVarRef{flp, getNode(dfgVarp), VAccess::WRITE};
AstConst* const idxp = new AstConst{flp, splicep->driverIndex(idx)};
AstArraySel* const lhsp = new AstArraySel{flp, refp, idxp};
// Add assignment of the value to the selected bits
addResultEquation(dfgVarp, flp, lhsp, rhsp);
if (DfgSpliceArray* const sArrayp = driverp->cast<DfgSpliceArray>()) {
// Partial assignment of array variable
sArrayp->forEachSourceEdge([&](const DfgEdge& edge, size_t i) {
UASSERT_OBJ(edge.sourcep(), sArrayp, "Should have removed undriven sources");
// Create ArraySel
FileLine* const dflp = sArrayp->driverFileLine(i);
AstConst* const idxp = new AstConst{dflp, sArrayp->driverIndex(i)};
AstArraySel* const nLhsp = new AstArraySel{dflp, lhsp->cloneTreePure(false), idxp};
// Convert source
convertDriver(scopep, dflp, nLhsp, edge.sourcep());
// Delete ArraySel if not consumed
if (!nLhsp->backp()) VL_DO_DANGLING(nLhsp->deleteTree(), nLhsp);
});
return;
}
UASSERT_OBJ(false, dfgVarp, "Should not have wholly driven arrays in Dfg");
driverp->v3fatalSrc("Unhandled DfgVertexSplice sub-type"); // LCOV_EXCL_LINE
}
// VISITORS
@@ -294,14 +286,13 @@ class DfgToAstVisitor final : DfgVisitor {
// If there is no driver (this vertex is an input to the graph), then nothing to do.
if (!vtx.srcp()) continue;
// Render packed variable assignments
if (const DfgVarPacked* const dfgVarp = vtx.cast<DfgVarPacked>()) {
convertPackedDriver(dfgVarp);
continue;
}
// Render array variable assignments
convertArrayDiver(vtx.as<DfgVarArray>());
// Render variable assignments
FileLine* const flp = vtx.driverFileLine() ? vtx.driverFileLine() : vtx.fileline();
AstScope* const scopep = T_Scoped ? vtx.varScopep()->scopep() : nullptr;
AstVarRef* const lhsp = new AstVarRef{flp, getNode(&vtx), VAccess::WRITE};
convertDriver(scopep, flp, lhsp, vtx.srcp());
// convetDriver clones and might not use up the original lhsp
if (!lhsp->backp()) VL_DO_DANGLING(lhsp->deleteTree(), lhsp);
}
}