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Fix ALWCOMBORDER on variable ordering (#7350) (#7608)

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2026-05-26 06:40:55 -04:00
committed by GitHub
parent a2d4b90b52
commit 9e2fedee6f
6 changed files with 126 additions and 18 deletions
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src/V3Undriven.cpp
+33 -8
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@@ -42,6 +42,7 @@ class UndrivenVarEntry final {
AstVar* const m_varp; // Variable this tracks
std::vector<bool> m_wholeFlags; // Used/Driven on whole vector
std::vector<bool> m_bitFlags; // Used/Driven on each subbit
const AstNode* m_usedNotDrivenp = nullptr; // First read before any write
const AstAlways* m_alwCombp
= nullptr; // always_comb of var if driven within always_comb, else nullptr
const FileLine* m_alwCombFileLinep = nullptr; // File line of always_comb of var if driven
@@ -82,6 +83,10 @@ private:
bool drivenFlag(int bit) const {
return m_wholeFlags[FLAG_DRIVEN] || m_bitFlags[bit * FLAGS_PER_BIT + FLAG_DRIVEN];
}
int bitCount() const { return m_bitFlags.size() / FLAGS_PER_BIT; }
void recordUsedNotDriven(const AstNode* nodep) {
if (!m_usedNotDrivenp) m_usedNotDrivenp = nodep;
}
enum BitNamesWhich : uint8_t { BN_UNUSED, BN_UNDRIVEN, BN_BOTH };
string bitNames(BitNamesWhich which) {
string bits;
@@ -121,6 +126,14 @@ private:
public:
void usedWhole(const AstNode* nodep) {
UINFO(9, "set u[*] " << m_varp->name() << " " << nodep);
if (!m_wholeFlags[FLAG_DRIVEN]) {
for (int bit = 0; bit < bitCount(); ++bit) {
if (!drivenFlag(bit)) {
recordUsedNotDriven(nodep);
break;
}
}
}
m_wholeFlags[FLAG_USED] = true;
}
void drivenWhole(const AstNode* nodep) {
@@ -156,10 +169,13 @@ public:
const FileLine* getNodeFileLinep() const { return m_nodeFileLinep; }
const AstAlways* getAlwCombp() const { return m_alwCombp; }
const FileLine* getAlwCombFileLinep() const { return m_alwCombFileLinep; }
void usedBit(int bit, int width) {
void usedBit(int bit, int width, const AstNode* nodep) {
UINFO(9, "set u[" << (bit + width - 1) << ":" << bit << "] " << m_varp->name());
for (int i = 0; i < width; i++) {
if (bitNumOk(bit + i)) m_bitFlags[(bit + i) * FLAGS_PER_BIT + FLAG_USED] = true;
if (bitNumOk(bit + i)) {
if (!drivenFlag(bit + i)) recordUsedNotDriven(nodep);
m_bitFlags[(bit + i) * FLAGS_PER_BIT + FLAG_USED] = true;
}
}
}
void drivenBit(int bit, int width) {
@@ -181,6 +197,7 @@ public:
bool isUsedNotDrivenAny() const {
return isUsedNotDrivenBit(0, m_bitFlags.size() / FLAGS_PER_BIT);
}
const AstNode* firstUsedNotDrivenp() const { return m_usedNotDrivenp; }
static bool unusedMatch(AstVar* nodep) {
const string regexp = v3Global.opt.unusedRegexp();
if (regexp == "") return false;
@@ -374,7 +391,7 @@ class UndrivenVisitor final : public VNVisitorConst {
}
}
void warnAlwCombOrder(AstNodeVarRef* nodep) {
void warnAlwCombOrder(AstNodeVarRef* nodep, const AstNode* readp) {
AstVar* const varp = nodep->varp();
if (!varp->isParam() && !varp->isGenVar() && !varp->isUsedLoopIdx()
&& !varp->ignoreSchedWrite()
@@ -382,8 +399,16 @@ class UndrivenVisitor final : public VNVisitorConst {
&& !VN_IS(nodep, VarXRef) // Xrefs might point at two different instances
&& !varp->fileline()->warnIsOff(
V3ErrorCode::ALWCOMBORDER)) { // Warn only once per variable
nodep->v3warn(ALWCOMBORDER,
"Always_comb variable driven after use: " << nodep->prettyNameQ());
nodep->v3warn(
ALWCOMBORDER,
"always_comb reads " << nodep->prettyNameQ()
<< " before assigning it later in the same block; behavior "
"may imply latch/state-like behavior and is not purely "
"combinational"
<< (readp ? "\n" + readp->warnOther()
+ "... Location of earlier read\n"
+ readp->warnContextSecondary()
: ""));
varp->fileline()->modifyWarnOff(V3ErrorCode::ALWCOMBORDER,
true); // Complain just once for any usage
}
@@ -433,12 +458,12 @@ class UndrivenVisitor final : public VNVisitorConst {
if (usr == 2 && m_alwaysCombp
&& entryp->isUsedNotDrivenBit(lsb, nodep->width())) {
UINFO(9, " Select. Entryp=" << cvtToHex(entryp));
warnAlwCombOrder(varrefp);
warnAlwCombOrder(varrefp, entryp->firstUsedNotDrivenp());
}
entryp->drivenBit(lsb, nodep->width());
}
if (m_inBBox || !varrefp->access().isWriteOrRW())
entryp->usedBit(lsb, nodep->width());
entryp->usedBit(lsb, nodep->width(), varrefp);
}
} else {
// else other varrefs handled as unknown mess in AstVarRef
@@ -487,7 +512,7 @@ class UndrivenVisitor final : public VNVisitorConst {
if (m_inBBox || nodep->access().isWriteOrRW()) {
if (usr == 2 && m_alwaysCombp && entryp->isUsedNotDrivenAny()) {
UINFO(9, " Full bus. Entryp=" << cvtToHex(entryp));
warnAlwCombOrder(nodep);
warnAlwCombOrder(nodep, entryp->firstUsedNotDrivenp());
}
if (entryp->isDrivenWhole() && !m_inBBox && !VN_IS(nodep, VarXRef)
&& !VN_IS(nodep->dtypep()->skipRefp(), UnpackArrayDType)