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Add Dfg cycle breaking support

This commit is contained in:
Geza Lore 2026-06-19 17:33:50 +01:00
parent 75027c6712
commit b62d74a055
2 changed files with 128 additions and 6 deletions
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52
src/V3DfgBreakCycles.cpp
View File

@ -332,12 +332,25 @@ class TraceDriver final : public DfgVisitor {
}
void visit(DfgArraySel* vtxp) override {
// Only constant select
const DfgConst* const idxp = vtxp->bitp()->cast<DfgConst>();
if (!idxp) return;
// From a variable
const DfgVarArray* varp = vtxp->fromp()->cast<DfgVarArray>();
if (!varp) return;
// If index is not constant, independence was proven only if the 'fromp' is
// independent, so no need to trace that
if (!vtxp->bitp()->is<DfgConst>()) {
DfgArraySel* const resp = make<DfgArraySel>(vtxp, vtxp->width());
resp->fromp(vtxp->fromp());
resp->bitp(trace(vtxp->bitp(), vtxp->bitp()->width() - 1, 0));
DfgSel* const selp = make<DfgSel>(vtxp, m_msb - m_lsb + 1);
selp->fromp(resp);
selp->lsb(m_lsb);
SET_RESULT(selp);
return;
}
// Trace the relevant driver based on the static index
const DfgConst* const idxp = vtxp->bitp()->as<DfgConst>();
UASSERT_OBJ(!varp->isVolatile(), vtxp, "Should not trace through volatile VarArray");
// Skip through intermediate variables
while (varp->srcp() && varp->srcp()->is<DfgVarArray>()) {
@ -589,6 +602,16 @@ class TraceDriver final : public DfgVisitor {
SET_RESULT(resp);
}
void visit(DfgMatchMasked* vtxp) override {
DfgMatchMasked* const resp = make<DfgMatchMasked>(vtxp, vtxp->width());
resp->lhsp(trace(vtxp->lhsp(), vtxp->lhsp()->width() - 1, 0));
resp->matchp(trace(vtxp->matchp(), vtxp->matchp()->width() - 1, 0));
DfgSel* const selp = make<DfgSel>(vtxp, m_msb - m_lsb + 1);
selp->fromp(resp);
selp->lsb(m_lsb);
SET_RESULT(resp);
}
#undef SET_RESULT
public:
@ -721,12 +744,23 @@ class IndependentBits final : public DfgVisitor {
}
void visit(DfgArraySel* vtxp) override {
// Only constant select
const DfgConst* const idxp = vtxp->bitp()->cast<DfgConst>();
if (!idxp) return;
// From a variable
const DfgVarArray* varp = vtxp->fromp()->cast<DfgVarArray>();
if (!varp) return;
// If index is not constant, independent only if the variable index
// is indenpendent and the array is independent. We don't track arrays,
// so we will assume an array is only independent if it has no drivers
// in the graph. TODO: could check all drivers.
if (!vtxp->bitp()->is<DfgConst>()) {
if (MASK(vtxp->bitp()).isEqAllOnes() && !varp->srcp() && !varp->defaultp()) {
MASK(vtxp).setAllBits1();
}
return;
}
// Trace the relevant driver based on the static index
const DfgConst* const idxp = vtxp->bitp()->as<DfgConst>();
// We cannot trace through a volatile variable, so pretend all bits are dependent
if (varp->isVolatile()) return;
// Skip through intermediate variables
@ -954,6 +988,12 @@ class IndependentBits final : public DfgVisitor {
}
}
void visit(DfgMatchMasked* vtxp) override {
if (MASK(vtxp->lhsp()).isEqAllOnes() && MASK(vtxp->matchp()).isEqAllOnes()) { //
MASK(vtxp).setAllBits1();
}
}
#undef MASK
// Enqueue sinks of vertex to work list for traversal - only called from constructor

82
test_regress/t/t_dfg_break_cycles.v
View File

@ -436,4 +436,86 @@ module t (
assign VOLATILE_ARRAY_IN_CYCLE_1 = volatile_array_in_cycle_1a[1];
// verilator lint_on
//////////////////////////////////////////////////////////////////////////
// Match masked
//////////////////////////////////////////////////////////////////////////
logic [63:0] match_masked; // UNOPTFLAT
always_comb begin
casez (rand_a[31:0])
32'b????????_????????_????????_???????1 : match_masked[31:0] = 32'd00;
32'b????????_????????_????????_??????1? : match_masked[31:0] = 32'd01;
32'b????????_????????_????????_?????1?? : match_masked[31:0] = 32'd02;
32'b????????_????????_????????_????1??? : match_masked[31:0] = 32'd03;
32'b????????_????????_????????_???1???? : match_masked[31:0] = 32'd04;
32'b????????_????????_????????_??1????? : match_masked[31:0] = 32'd05;
32'b????????_????????_????????_?1?????? : match_masked[31:0] = 32'd06;
32'b????????_????????_????????_1??????? : match_masked[31:0] = 32'd07;
32'b????????_????????_???????1_???????? : match_masked[31:0] = 32'd08;
32'b????????_????????_??????1?_???????? : match_masked[31:0] = 32'd09;
32'b????????_????????_?????1??_???????? : match_masked[31:0] = 32'd10;
32'b????????_????????_????1???_???????? : match_masked[31:0] = 32'd11;
32'b????????_????????_???1????_???????? : match_masked[31:0] = 32'd12;
32'b????????_????????_??1?????_???????? : match_masked[31:0] = 32'd13;
32'b????????_????????_?1??????_???????? : match_masked[31:0] = 32'd14;
32'b????????_????????_1???????_???????? : match_masked[31:0] = 32'd15;
32'b????????_???????1_????????_???????? : match_masked[31:0] = 32'd16;
32'b????????_??????1?_????????_???????? : match_masked[31:0] = 32'd17;
32'b????????_?????1??_????????_???????? : match_masked[31:0] = 32'd18;
32'b????????_????1???_????????_???????? : match_masked[31:0] = 32'd19;
32'b????????_???1????_????????_???????? : match_masked[31:0] = 32'd20;
32'b????????_??1?????_????????_???????? : match_masked[31:0] = 32'd21;
32'b????????_?1??????_????????_???????? : match_masked[31:0] = 32'd22;
32'b????????_1???????_????????_???????? : match_masked[31:0] = 32'd23;
32'b???????1_????????_????????_???????? : match_masked[31:0] = 32'd24;
32'b??????1?_????????_????????_???????? : match_masked[31:0] = 32'd25;
32'b?????1??_????????_????????_???????? : match_masked[31:0] = 32'd26;
32'b????1???_????????_????????_???????? : match_masked[31:0] = 32'd27;
32'b???1????_????????_????????_???????? : match_masked[31:0] = 32'd28;
32'b??1?????_????????_????????_???????? : match_masked[31:0] = 32'd29;
32'b?1??????_????????_????????_???????? : match_masked[31:0] = 32'd30;
32'b1???????_????????_????????_???????? : match_masked[31:0] = 32'd31;
default : match_masked[31:0] = '1;
endcase
end
always_comb begin
casez (match_masked[31:0])
32'd00 : match_masked[63:32] = 32'b00000000_00000000_00000000_00000001;
32'd01 : match_masked[63:32] = 32'b00000000_00000000_00000000_00000010;
32'd02 : match_masked[63:32] = 32'b00000000_00000000_00000000_00000100;
32'd03 : match_masked[63:32] = 32'b00000000_00000000_00000000_00001000;
32'd04 : match_masked[63:32] = 32'b00000000_00000000_00000000_00010000;
32'd05 : match_masked[63:32] = 32'b00000000_00000000_00000000_00100000;
32'd06 : match_masked[63:32] = 32'b00000000_00000000_00000000_01000000;
32'd07 : match_masked[63:32] = 32'b00000000_00000000_00000000_10000000;
32'd08 : match_masked[63:32] = 32'b00000000_00000000_00000001_00000000;
32'd09 : match_masked[63:32] = 32'b00000000_00000000_00000010_00000000;
32'd10 : match_masked[63:32] = 32'b00000000_00000000_00000100_00000000;
32'd11 : match_masked[63:32] = 32'b00000000_00000000_00001000_00000000;
32'd12 : match_masked[63:32] = 32'b00000000_00000000_00010000_00000000;
32'd13 : match_masked[63:32] = 32'b00000000_00000000_00100000_00000000;
32'd14 : match_masked[63:32] = 32'b00000000_00000000_01000000_00000000;
32'd15 : match_masked[63:32] = 32'b00000000_00000000_10000000_00000000;
32'd16 : match_masked[63:32] = 32'b00000000_00000001_00000000_00000000;
32'd17 : match_masked[63:32] = 32'b00000000_00000010_00000000_00000000;
32'd18 : match_masked[63:32] = 32'b00000000_00000100_00000000_00000000;
32'd19 : match_masked[63:32] = 32'b00000000_00001000_00000000_00000000;
32'd20 : match_masked[63:32] = 32'b00000000_00010000_00000000_00000000;
32'd21 : match_masked[63:32] = 32'b00000000_00100000_00000000_00000000;
32'd22 : match_masked[63:32] = 32'b00000000_01000000_00000000_00000000;
32'd23 : match_masked[63:32] = 32'b00000000_10000000_00000000_00000000;
32'd24 : match_masked[63:32] = 32'b00000001_00000000_00000000_00000000;
32'd25 : match_masked[63:32] = 32'b00000010_00000000_00000000_00000000;
32'd26 : match_masked[63:32] = 32'b00000100_00000000_00000000_00000000;
32'd27 : match_masked[63:32] = 32'b00001000_00000000_00000000_00000000;
32'd28 : match_masked[63:32] = 32'b00010000_00000000_00000000_00000000;
32'd29 : match_masked[63:32] = 32'b00100000_00000000_00000000_00000000;
32'd30 : match_masked[63:32] = 32'b01000000_00000000_00000000_00000000;
32'd31 : match_masked[63:32] = 32'b10000000_00000000_00000000_00000000;
default: match_masked[63:32] = 32'b00000000_00000000_00000000_00000000;
endcase
end
`signal(MATCH_MASKED, 64);
assign MATCH_MASKED = match_masked;
endmodule