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Fix UNUSED / UNDRIVEN for unused functions (#6967)

This commit is contained in:
Todd Strader 2026-02-12 11:01:14 -05:00 committed by GitHub
parent 9b1b9a5b3b
commit fed41aba91
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GPG Key ID: B5690EEEBB952194
5 changed files with 144 additions and 21 deletions
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60
src/V3Undriven.cpp
View File

@ -51,6 +51,7 @@ class UndrivenVarEntry final {
const AstNode* m_procWritep = nullptr; // varref if written in process
const FileLine* m_nodeFileLinep = nullptr; // File line of varref if driven, else nullptr
bool m_underGen = false; // Under a generate
bool m_ftaskDriven = false; // Last driven by function or task
const AstNodeFTaskRef* m_callNodep = nullptr; // Call node if driven via writeSummary
@ -124,7 +125,8 @@ public:
UINFO(9, "set d[*] " << m_varp->name());
m_wholeFlags[FLAG_DRIVEN] = true;
}
void drivenWhole(const AstNodeVarRef* nodep, const FileLine* fileLinep) {
void drivenWhole(const AstNodeVarRef* nodep, const FileLine* fileLinep, bool ftaskDef) {
m_ftaskDriven = ftaskDef && !isDrivenWhole();
drivenWhole();
m_nodep = nodep;
m_nodeFileLinep = fileLinep;
@ -143,6 +145,7 @@ public:
bool isUnderGen() const { return m_underGen; }
bool isDrivenWhole() const { return m_wholeFlags[FLAG_DRIVEN]; }
bool isDrivenAlwaysCombWhole() const { return m_wholeFlags[FLAG_DRIVEN_ALWCOMB]; }
bool isFtaskDriven() const { return m_ftaskDriven; }
const AstNodeVarRef* getNodep() const { return m_nodep; }
const FileLine* getNodeFileLinep() const { return m_nodeFileLinep; }
const AstAlways* getAlwCombp() const { return m_alwCombp; }
@ -207,6 +210,8 @@ public:
true); // Warn only once
}
} else { // Signal
const string varType{nodep->isFuncLocal() ? "Function variable" : "Signal"};
bool funcInout = nodep->isFuncLocal() && nodep->isInout();
bool allU = true;
bool allD = true;
bool anyU = m_wholeFlags[FLAG_USED];
@ -225,6 +230,10 @@ public:
anyDnotU |= !used && driv;
anynotDU |= !used && !driv;
}
if (funcInout) {
if (anyD) allU = true;
allD = true;
}
if (allU) m_wholeFlags[FLAG_USED] = true;
if (allD) m_wholeFlags[FLAG_DRIVEN] = true;
// Test results
@ -239,37 +248,45 @@ public:
// thus undriven+unused bits get UNUSED warnings, as they're not as buggy.
if (!unusedMatch(nodep)) {
nodep->v3warn(UNUSEDSIGNAL,
"Signal is not driven, nor used: " << nodep->prettyNameQ());
varType << " is not driven, nor used: " << nodep->prettyNameQ());
nodep->fileline()->modifyWarnOff(V3ErrorCode::UNUSEDSIGNAL,
true); // Warn only once
}
} else if (allD && !anyU) {
if (!unusedMatch(nodep)) {
nodep->v3warn(UNUSEDSIGNAL, "Signal is not used: " << nodep->prettyNameQ());
nodep->v3warn(UNUSEDSIGNAL,
varType << " is not used: " << nodep->prettyNameQ());
nodep->fileline()->modifyWarnOff(V3ErrorCode::UNUSEDSIGNAL,
true); // Warn only once
}
} else if (!anyD && allU) {
nodep->v3warn(UNDRIVEN, "Signal is not driven: " << nodep->prettyNameQ());
nodep->v3warn(UNDRIVEN, varType << " is not driven: " << nodep->prettyNameQ());
nodep->fileline()->modifyWarnOff(V3ErrorCode::UNDRIVEN, true); // Warn only once
} else {
} else if (!funcInout) {
// Bits have different dispositions
const std::string varTypeLower = [&varType]() {
std::string str = varType;
str[0] = std::tolower(static_cast<unsigned char>(str[0]));
return str;
}();
bool setU = false;
bool setD = false;
if (anynotDU && !unusedMatch(nodep)) {
nodep->v3warn(UNUSEDSIGNAL, "Bits of signal are not driven, nor used: "
<< nodep->prettyNameQ() << bitNames(BN_BOTH));
nodep->v3warn(UNUSEDSIGNAL,
"Bits of " << varTypeLower << " are not driven, nor used: "
<< nodep->prettyNameQ() << bitNames(BN_BOTH));
setU = true;
}
if (anyDnotU && !unusedMatch(nodep)) {
nodep->v3warn(UNUSEDSIGNAL,
"Bits of signal are not used: " << nodep->prettyNameQ()
<< bitNames(BN_UNUSED));
nodep->v3warn(UNUSEDSIGNAL, "Bits of " << varTypeLower << " are not used: "
<< nodep->prettyNameQ()
<< bitNames(BN_UNUSED));
setU = true;
}
if (anyUnotD) {
nodep->v3warn(UNDRIVEN, "Bits of signal are not driven: "
<< nodep->prettyNameQ() << bitNames(BN_UNDRIVEN));
nodep->v3warn(UNDRIVEN, "Bits of " << varTypeLower << " are not driven: "
<< nodep->prettyNameQ()
<< bitNames(BN_UNDRIVEN));
setD = true;
}
if (setU) { // Warn only once
@ -354,18 +371,20 @@ class UndrivenVisitor final : public VNVisitorConst {
// VISITORS
void visit(AstVar* nodep) override {
const bool funcInout = nodep->isFuncLocal() && nodep->isInout();
for (int usr = 1; usr < (m_alwaysCombp ? 3 : 2); ++usr) {
// For assigns and non-combo always, do just usr==1, to look
// for module-wide undriven etc.
// For combo always, run both usr==1 for above, and also
// usr==2 for always-only checks.
UndrivenVarEntry* const entryp = getEntryp(nodep, usr);
if (nodep->isNonOutput() || nodep->isSigPublic() || nodep->isSigUserRWPublic()
if ((nodep->isNonOutput() && !funcInout) || nodep->isSigPublic()
|| nodep->isSigUserRWPublic()
|| (m_taskp && (m_taskp->dpiImport() || m_taskp->dpiExport()))) {
entryp->drivenWhole();
}
if (nodep->isWritable() || nodep->isSigPublic() || nodep->isSigUserRWPublic()
|| nodep->isSigUserRdPublic()
if ((nodep->isWritable() && !funcInout) || nodep->isSigPublic()
|| nodep->isSigUserRWPublic() || nodep->isSigUserRdPublic()
|| (m_taskp && (m_taskp->dpiImport() || m_taskp->dpiExport()))) {
entryp->usedWhole();
}
@ -433,12 +452,12 @@ class UndrivenVisitor final : public VNVisitorConst {
}
// If writeSummary is enabled, task/function definitions are treated as non-executed.
// Their effects are applied at call sites via writeSummary(), so don't let definition
// traversal create phantom "other writes" for MULTIDRIVEN.
// Remember that anything driven here doesn't count toward MULTIDRIVEN.
bool ftaskDef = false;
if (m_taskp && !m_alwaysp && !m_inContAssign && !m_inInitialStatic && !m_inBBox
&& !m_taskp->dpiExport()) {
AstVar* const retVarp = VN_CAST(m_taskp->fvarp(), Var);
if (!retVarp || nodep->varp() != retVarp) return;
if (!retVarp || nodep->varp() != retVarp) ftaskDef = true;
}
for (int usr = 1; usr < (m_alwaysCombp ? 3 : 2); ++usr) {
@ -453,7 +472,8 @@ class UndrivenVisitor final : public VNVisitorConst {
if (entryp->isDrivenWhole() && !m_inBBox && !VN_IS(nodep, VarXRef)
&& !VN_IS(nodep->dtypep()->skipRefp(), UnpackArrayDType)
&& nodep->fileline() != entryp->getNodeFileLinep() && !entryp->isUnderGen()
&& (entryp->getNodep() || entryp->callNodep())) {
&& (entryp->getNodep() || entryp->callNodep()) && !entryp->isFtaskDriven()
&& !ftaskDef) {
const AstNode* const otherWritep
= entryp->getNodep() ? static_cast<const AstNode*>(entryp->getNodep())
@ -483,7 +503,7 @@ class UndrivenVisitor final : public VNVisitorConst {
<< otherWritep->warnContextSecondary());
}
}
entryp->drivenWhole(nodep, nodep->fileline());
entryp->drivenWhole(nodep, nodep->fileline(), ftaskDef);
if (m_alwaysCombp && entryp->isDrivenAlwaysCombWhole()
&& m_alwaysCombp != entryp->getAlwCombp()
&& m_alwaysCombp->fileline() == entryp->getAlwCombFileLinep())

2
test_regress/t/t_lint_style_bad.out
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@ -23,7 +23,7 @@
| ^~~
... For warning description see https://verilator.org/warn/UNUSEDSIGNAL?v=latest
... Use "/* verilator lint_off UNUSEDSIGNAL */" and lint_on around source to disable this message.
%Warning-UNDRIVEN: t/t_lint_style_bad.v:12:14: Signal is not driven: 'top'
%Warning-UNDRIVEN: t/t_lint_style_bad.v:12:14: Function variable is not driven: 'top'
: ... note: In instance 't'
12 | output top;
| ^~~

29
test_regress/t/t_lint_unused_func_bad.out Normal file
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@ -0,0 +1,29 @@
%Warning-UNUSEDSIGNAL: t/t_lint_unused_func_bad.v:14:53: Function variable is not used: 'not_used'
: ... note: In instance 't'
14 | function automatic int unused_input_unused_func(int not_used);
| ^~~~~~~~
... For warning description see https://verilator.org/warn/UNUSEDSIGNAL?v=latest
... Use "/* verilator lint_off UNUSEDSIGNAL */" and lint_on around source to disable this message.
%Warning-UNDRIVEN: t/t_lint_unused_func_bad.v:20:7: Function variable is not driven: 'not_driven'
: ... note: In instance 't'
20 | int not_driven;
| ^~~~~~~~~~
... For warning description see https://verilator.org/warn/UNDRIVEN?v=latest
... Use "/* verilator lint_off UNDRIVEN */" and lint_on around source to disable this message.
%Warning-UNDRIVEN: t/t_lint_unused_func_bad.v:25:7: Function variable is not driven: 'undriven_result'
: ... note: In instance 't'
25 | int undriven_result;
| ^~~~~~~~~~~~~~~
%Warning-UNDRIVEN: t/t_lint_unused_func_bad.v:29:52: Function variable is not driven: 'undriven_out_param'
: ... note: In instance 't'
29 | function automatic void undriven_output(output int undriven_out_param);
| ^~~~~~~~~~~~~~~~~~
%Warning-UNUSEDSIGNAL: t/t_lint_unused_func_bad.v:32:51: Function variable is not driven, nor used: 'untouched_inout_param'
: ... note: In instance 't'
32 | function automatic void untouched_inout(inout int untouched_inout_param);
| ^~~~~~~~~~~~~~~~~~~~~
%Warning-UNUSEDSIGNAL: t/t_lint_unused_func_bad.v:35:63: Function variable is not driven, nor used: 'untouched_inout_unused_func_param'
: ... note: In instance 't'
35 | function automatic void untouched_inout_unused_func(inout int untouched_inout_unused_func_param);
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
%Error: Exiting due to

20
test_regress/t/t_lint_unused_func_bad.py Executable file
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@ -0,0 +1,20 @@
#!/usr/bin/env python3
# DESCRIPTION: Verilator: Verilog Test driver/expect definition
#
# This program is free software; you can redistribute it and/or modify it
# under the terms of either the GNU Lesser General Public License Version 3
# or the Perl Artistic License Version 2.0.
# SPDX-FileCopyrightText: 2025 Wilson Snyder
# SPDX-License-Identifier: LGPL-3.0-only OR Artistic-2.0
import vltest_bootstrap
test.scenarios("simulator")
test.compile(
verilator_flags2=["--lint-only -Wall -Wno-DECLFILENAME --unused-regexp blargh"],
fails=True,
expect_filename=test.golden_filename,
)
test.passes()

54
test_regress/t/t_lint_unused_func_bad.v Normal file
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@ -0,0 +1,54 @@
// DESCRIPTION: Verilator: Verilog Test module
//
// This file ONLY is placed under the Creative Commons Public Domain.
// SPDX-FileCopyrightText: 2026 Wilson Snyder
// SPDX-License-Identifier: CC0-1.0
function automatic int ok_unused_func(real val);
int result = $rtoi(val);
bit huh = result[0];
return result + huh;
endfunction
// Unused parameter
function automatic int unused_input_unused_func(int not_used);
return 5;
endfunction
// Undriven variable
function automatic int undriven_var_unused_func(int some_val);
int not_driven;
return some_val + not_driven;
endfunction
function automatic int undriven_var();
int undriven_result;
return undriven_result;
endfunction
function automatic void undriven_output(output int undriven_out_param);
endfunction
function automatic void untouched_inout(inout int untouched_inout_param);
endfunction
function automatic void untouched_inout_unused_func(inout int untouched_inout_unused_func_param);
endfunction
function automatic void driven_inout_unused_func(inout int driven_inout_unused_func_param);
driven_inout_unused_func_param = 7;
endfunction
function automatic void used_inout_unused_func(inout int used_inout_unused_func_param);
$display(used_inout_unused_func_param);
endfunction
module t;
int result;
initial begin
result = undriven_var();
undriven_output(result);
untouched_inout(result);
$display(result);
end
endmodule