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Use a pointer to store the LHS of assignments with LHS with side effects
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@PetroZarytskyi @vgvassilev
PetroZarytskyi authored and vgvassilev committed Jul 22, 2024
1 parent 28dea37 commit e9af768
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Showing 5 changed files with 60 additions and 76 deletions.
3 changes: 1 addition & 2 deletions include/clad/Differentiator/ReverseModeVisitor.h
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Original file line number Diff line number Diff line change
Expand Up @@ -254,8 +254,7 @@ namespace clad {
clang::Expr* GlobalStoreAndRef(clang::Expr* E,
llvm::StringRef prefix = "_t",
bool force = false);
StmtDiff StoreAndRestore(clang::Expr* E, llvm::StringRef prefix = "_t",
bool force = false);
StmtDiff StoreAndRestore(clang::Expr* E, llvm::StringRef prefix = "_t");

//// A type returned by DelayedGlobalStoreAndRef
/// .Result is a reference to the created (yet uninitialized) global
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3 changes: 2 additions & 1 deletion lib/Differentiator/DiffPlanner.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -562,7 +562,8 @@ namespace clad {
}

bool DiffRequest::shouldBeRecorded(Expr* E) const {
assert(EnableTBRAnalysis && "TBR not enabled!");
if (!EnableTBRAnalysis)
return true;

if (!isa<DeclRefExpr>(E) && !isa<ArraySubscriptExpr>(E) &&
!isa<MemberExpr>(E))
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64 changes: 25 additions & 39 deletions lib/Differentiator/ReverseModeVisitor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2033,7 +2033,7 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
Expr* diff_dx = diff.getExpr_dx();
if (isPointerOp)
addToCurrentBlock(BuildOp(opCode, diff_dx), direction::forward);
if (UsefulToStoreGlobal(diff.getRevSweepAsExpr())) {
if (m_DiffReq.shouldBeRecorded(E)) {
auto op = opCode == UO_PostInc ? UO_PostDec : UO_PostInc;
addToCurrentBlock(BuildOp(op, Clone(diff.getRevSweepAsExpr())),
direction::reverse);
Expand All @@ -2050,7 +2050,7 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
Expr* diff_dx = diff.getExpr_dx();
if (isPointerOp)
addToCurrentBlock(BuildOp(opCode, diff_dx), direction::forward);
if (UsefulToStoreGlobal(diff.getRevSweepAsExpr())) {
if (m_DiffReq.shouldBeRecorded(E)) {
auto op = opCode == UO_PreInc ? UO_PreDec : UO_PreInc;
addToCurrentBlock(BuildOp(op, Clone(diff.getRevSweepAsExpr())),
direction::reverse);
Expand Down Expand Up @@ -2332,24 +2332,15 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
// in Lblock
beginBlock(direction::reverse);
Ldiff = Visit(L, dfdx());
auto* Lblock = endBlock(direction::reverse);
llvm::SmallVector<Expr*, 4> ExprsToStore;
utils::GetInnermostReturnExpr(Ldiff.getExpr(), ExprsToStore);

// We need to store values of derivative pointer variables in forward pass
// and restore them in reverse pass.
if (isPointerOp) {
Expr* Edx = Ldiff.getExpr_dx();
ExprsToStore.push_back(Edx);
}

if (L->HasSideEffects(m_Context)) {
Expr* E = Ldiff.getExpr();
auto* storeE =
StoreAndRef(E, m_Context.getLValueReferenceType(E->getType()));
Ldiff.updateStmt(storeE);
auto* storeE = GlobalStoreAndRef(BuildOp(UO_AddrOf, E));
Ldiff.updateStmt(BuildOp(UO_Deref, storeE));
}

Stmts Lblock = EndBlockWithoutCreatingCS(direction::reverse);

Expr* LCloned = Ldiff.getExpr();
// For x, AssignedDiff is _d_x, for x[i] its _d_x[i], for reference exprs
// like (x = y) it propagates recursively, so _d_x is also returned.
Expand All @@ -2358,16 +2349,23 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
return Clone(BinOp);
ResultRef = AssignedDiff;
// If assigned expr is dependent, first update its derivative;
auto Lblock_begin = Lblock->body_rbegin();
auto Lblock_end = Lblock->body_rend();
if (dfdx() && !Lblock.empty()) {
addToCurrentBlock(*Lblock.begin(), direction::reverse);
Lblock.erase(Lblock.begin());
}

if (dfdx() && Lblock_begin != Lblock_end) {
addToCurrentBlock(*Lblock_begin, direction::reverse);
Lblock_begin = std::next(Lblock_begin);
// Store the value of the LHS of the assignment in the forward pass
// and restore it in the reverse pass
if (m_DiffReq.shouldBeRecorded(L)) {
StmtDiff pushPop = StoreAndRestore(LCloned);
addToCurrentBlock(pushPop.getExpr(), direction::forward);
addToCurrentBlock(pushPop.getExpr_dx(), direction::reverse);
}

for (auto& E : ExprsToStore) {
auto pushPop = StoreAndRestore(E);
// We need to store values of derivative pointer variables in forward pass
// and restore them in reverse pass.
if (isPointerOp) {
StmtDiff pushPop = StoreAndRestore(Ldiff.getExpr_dx());
addToCurrentBlock(pushPop.getExpr(), direction::forward);
addToCurrentBlock(pushPop.getExpr_dx(), direction::reverse);
}
Expand Down Expand Up @@ -2469,8 +2467,8 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
opCode);

// Output statements from Visit(L).
for (auto it = Lblock_begin; it != Lblock_end; ++it)
addToCurrentBlock(*it, direction::reverse);
for (Stmt* S : Lblock)
addToCurrentBlock(S, direction::reverse);
} else if (opCode == BO_Comma) {
auto* zero =
ConstantFolder::synthesizeLiteral(m_Context.IntTy, m_Context, 0);
Expand Down Expand Up @@ -2736,8 +2734,7 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
initDiff.getForwSweepExpr_dx()));
addToCurrentBlock(assignDerivativeE);
if (isInsideLoop) {
StmtDiff pushPop =
StoreAndRestore(derivedVDE, /*prefix=*/"_t", /*force=*/true);
StmtDiff pushPop = StoreAndRestore(derivedVDE);
addToCurrentBlock(pushPop.getExpr(), direction::forward);
m_LoopBlock.back().push_back(pushPop.getExpr_dx());
}
Expand Down Expand Up @@ -2922,8 +2919,7 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
auto* declRef = BuildDeclRef(decl);
auto* assignment = BuildOp(BO_Assign, declRef, decl->getInit());
if (isInsideLoop) {
auto pushPop =
StoreAndRestore(declRef, /*prefix=*/"_t", /*force=*/true);
auto pushPop = StoreAndRestore(declRef);
if (pushPop.getExpr() != declRef)
addToCurrentBlock(pushPop.getExpr_dx(), direction::reverse);
assignment = BuildOp(BO_Comma, pushPop.getExpr(), assignment);
Expand Down Expand Up @@ -3104,12 +3100,6 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
if (isa<CallExpr>(B))
return false;

// FIXME: Here will be the entry point of the advanced activity analysis.

// Check if the expression was marked as to-be recorded by an analysis.
if (m_DiffReq.EnableTBRAnalysis)
return m_DiffReq.shouldBeRecorded(B);

// Assume E is useful to store.
return true;
}
Expand Down Expand Up @@ -3171,13 +3161,9 @@ Expr* getArraySizeExpr(const ArrayType* AT, ASTContext& context,
}

StmtDiff ReverseModeVisitor::StoreAndRestore(clang::Expr* E,
llvm::StringRef prefix,
bool force) {
llvm::StringRef prefix) {
auto Type = getNonConstType(E->getType(), m_Context, m_Sema);

if (!force && !UsefulToStoreGlobal(E))
return {};

if (isInsideLoop) {
auto CladTape = MakeCladTapeFor(Clone(E), prefix);
Expr* Push = CladTape.Push;
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32 changes: 15 additions & 17 deletions lib/Differentiator/TBRAnalyzer.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -295,17 +295,7 @@ void TBRAnalyzer::addVar(const clang::VarDecl* VD, bool forceNonRefType) {
}

void TBRAnalyzer::markLocation(const clang::Expr* E) {
VarData* data = getExprVarData(E);
if (!data || findReq(*data)) {
// FIXME: If any of the data's child nodes are required to store then data
// itself is stored. We might add an option to store separate fields.
// FIXME: Sometimes one location might correspond to multiple stores. For
// example, in ``(x*=y)=u`` x's location will first be marked as required to
// be stored (when passing *= operator) but then marked as not required to
// be stored (when passing = operator). Current method of marking locations
// does not allow to differentiate between these two.
m_TBRLocs.insert(E->getBeginLoc());
}
m_TBRLocs.insert(E->getBeginLoc());
}

void TBRAnalyzer::setIsRequired(const clang::Expr* E, bool isReq) {
Expand Down Expand Up @@ -703,15 +693,19 @@ bool TBRAnalyzer::VisitBinaryOperator(BinaryOperator* BinOp) {
}
llvm::SmallVector<Expr*, 4> ExprsToStore;
utils::GetInnermostReturnExpr(L, ExprsToStore);
bool hasToBeSetReq = false;
for (const auto* innerExpr : ExprsToStore) {
// Mark corresponding SourceLocation as required/not required to be
// stored for all expressions that could be used changed.
markLocation(innerExpr);
// If at least one of ExprsToStore has to be stored,
// mark L as useful to store.
if (VarData* data = getExprVarData(innerExpr))
hasToBeSetReq = hasToBeSetReq || findReq(*data);
// Set them to not required to store because the values were changed.
// (if some value was not changed, this could only happen if it was
// already not required to store).
setIsRequired(innerExpr, /*isReq=*/false);
}
if (hasToBeSetReq)
markLocation(L);
} else if (opCode == BO_Comma) {
setMode(0);
TraverseStmt(L);
Expand All @@ -737,9 +731,13 @@ bool TBRAnalyzer::VisitUnaryOperator(clang::UnaryOperator* UnOp) {
llvm::SmallVector<Expr*, 4> ExprsToStore;
utils::GetInnermostReturnExpr(E, ExprsToStore);
for (const auto* innerExpr : ExprsToStore) {
// Mark corresponding SourceLocation as required/not required to be
// stored for all expressions that could be changed.
markLocation(innerExpr);
// If at least one of ExprsToStore has to be stored,
// mark L as useful to store.
if (VarData* data = getExprVarData(innerExpr))
if (findReq(*data)) {
markLocation(E);
break;
}
}
}
// FIXME: Ideally, `__real` and `__imag` operators should be treated as member
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34 changes: 17 additions & 17 deletions test/Gradient/Assignments.C
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Original file line number Diff line number Diff line change
Expand Up @@ -414,19 +414,20 @@ double f9(double x, double y) {
//CHECK: void f9_grad(double x, double y, double *_d_x, double *_d_y) {
//CHECK-NEXT: double _d_t = 0;
//CHECK-NEXT: double _t0;
//CHECK-NEXT: double *_t1;
//CHECK-NEXT: double _t2;
//CHECK-NEXT: double t = x;
//CHECK-NEXT: _t0 = t;
//CHECK-NEXT: double &_t1 = (t *= x);
//CHECK-NEXT: _t2 = t;
//CHECK-NEXT: _t1 *= y;
//CHECK-NEXT: _t1 = &(t *= x);
//CHECK-NEXT: _t2 = *_t1;
//CHECK-NEXT: *_t1 *= y;
//CHECK-NEXT: _d_t += 1;
//CHECK-NEXT: {
//CHECK-NEXT: t = _t2;
//CHECK-NEXT: *_t1 = _t2;
//CHECK-NEXT: double _r_d1 = _d_t;
//CHECK-NEXT: _d_t = 0;
//CHECK-NEXT: _d_t += _r_d1 * y;
//CHECK-NEXT: *_d_y += _t1 * _r_d1;
//CHECK-NEXT: *_d_y += *_t1 * _r_d1;
//CHECK-NEXT: t = _t0;
//CHECK-NEXT: double _r_d0 = _d_t;
//CHECK-NEXT: _d_t = 0;
Expand Down Expand Up @@ -473,15 +474,16 @@ double f11(double x, double y) {
//CHECK: void f11_grad(double x, double y, double *_d_x, double *_d_y) {
//CHECK-NEXT: double _d_t = 0;
//CHECK-NEXT: double _t0;
//CHECK-NEXT: double *_t1;
//CHECK-NEXT: double _t2;
//CHECK-NEXT: double t = x;
//CHECK-NEXT: _t0 = t;
//CHECK-NEXT: double &_t1 = (t = x);
//CHECK-NEXT: _t2 = t;
//CHECK-NEXT: _t1 = y;
//CHECK-NEXT: _t1 = &(t = x);
//CHECK-NEXT: _t2 = *_t1;
//CHECK-NEXT: *_t1 = y;
//CHECK-NEXT: _d_t += 1;
//CHECK-NEXT: {
//CHECK-NEXT: t = _t2;
//CHECK-NEXT: *_t1 = _t2;
//CHECK-NEXT: double _r_d1 = _d_t;
//CHECK-NEXT: _d_t = 0;
//CHECK-NEXT: *_d_y += _r_d1;
Expand All @@ -504,26 +506,24 @@ double f12(double x, double y) {
//CHECK-NEXT: bool _cond0;
//CHECK-NEXT: double _t0;
//CHECK-NEXT: double _t1;
//CHECK-NEXT: double *_t2;
//CHECK-NEXT: double _t3;
//CHECK-NEXT: double _t4;
//CHECK-NEXT: double t;
//CHECK-NEXT: _cond0 = x > y;
//CHECK-NEXT: if (_cond0)
//CHECK-NEXT: _t0 = t;
//CHECK-NEXT: else
//CHECK-NEXT: _t1 = t;
//CHECK-NEXT: double &_t2 = (_cond0 ? (t = x) : (t = y));
//CHECK-NEXT: _t3 = t;
//CHECK-NEXT: _t4 = t;
//CHECK-NEXT: _t2 *= y;
//CHECK-NEXT: _t2 = &(_cond0 ? (t = x) : (t = y));
//CHECK-NEXT: _t3 = *_t2;
//CHECK-NEXT: *_t2 *= y;
//CHECK-NEXT: _d_t += 1;
//CHECK-NEXT: {
//CHECK-NEXT: t = _t3;
//CHECK-NEXT: t = _t4;
//CHECK-NEXT: *_t2 = _t3;
//CHECK-NEXT: double _r_d2 = (_cond0 ? _d_t : _d_t);
//CHECK-NEXT: (_cond0 ? _d_t : _d_t) = 0;
//CHECK-NEXT: (_cond0 ? _d_t : _d_t) += _r_d2 * y;
//CHECK-NEXT: *_d_y += _t2 * _r_d2;
//CHECK-NEXT: *_d_y += *_t2 * _r_d2;
//CHECK-NEXT: if (_cond0) {
//CHECK-NEXT: t = _t0;
//CHECK-NEXT: double _r_d0 = _d_t;
Expand Down

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