| |
| /* Compiler implementation of the D programming language |
| * Copyright (C) 1999-2021 by The D Language Foundation, All Rights Reserved |
| * written by Walter Bright |
| * http://www.digitalmars.com |
| * Distributed under the Boost Software License, Version 1.0. |
| * http://www.boost.org/LICENSE_1_0.txt |
| * https://github.com/D-Programming-Language/dmd/blob/master/src/sideeffect.c |
| */ |
| |
| #include "root/dsystem.h" |
| |
| #include "mars.h" |
| #include "init.h" |
| #include "expression.h" |
| #include "template.h" |
| #include "statement.h" |
| #include "mtype.h" |
| #include "utf.h" |
| #include "declaration.h" |
| #include "aggregate.h" |
| #include "scope.h" |
| #include "attrib.h" |
| #include "tokens.h" |
| |
| bool walkPostorder(Expression *e, StoppableVisitor *v); |
| bool lambdaHasSideEffect(Expression *e); |
| |
| /************************************************** |
| * Front-end expression rewriting should create temporary variables for |
| * non trivial sub-expressions in order to: |
| * 1. save evaluation order |
| * 2. prevent sharing of sub-expression in AST |
| */ |
| bool isTrivialExp(Expression *e) |
| { |
| class IsTrivialExp : public StoppableVisitor |
| { |
| public: |
| IsTrivialExp() {} |
| |
| void visit(Expression *e) |
| { |
| /* Bugzilla 11201: CallExp is always non trivial expression, |
| * especially for inlining. |
| */ |
| if (e->op == TOKcall) |
| { |
| stop = true; |
| return; |
| } |
| |
| // stop walking if we determine this expression has side effects |
| stop = lambdaHasSideEffect(e); |
| } |
| }; |
| |
| IsTrivialExp v; |
| return walkPostorder(e, &v) == false; |
| } |
| |
| /******************************************** |
| * Determine if Expression has any side effects. |
| */ |
| |
| bool hasSideEffect(Expression *e) |
| { |
| class LambdaHasSideEffect : public StoppableVisitor |
| { |
| public: |
| LambdaHasSideEffect() {} |
| |
| void visit(Expression *e) |
| { |
| // stop walking if we determine this expression has side effects |
| stop = lambdaHasSideEffect(e); |
| } |
| }; |
| |
| LambdaHasSideEffect v; |
| return walkPostorder(e, &v); |
| } |
| |
| /******************************************** |
| * Determine if the call of f, or function type or delegate type t1, has any side effects. |
| * Returns: |
| * 0 has any side effects |
| * 1 nothrow + constant purity |
| * 2 nothrow + strong purity |
| */ |
| |
| int callSideEffectLevel(FuncDeclaration *f) |
| { |
| /* Bugzilla 12760: ctor call always has side effects. |
| */ |
| if (f->isCtorDeclaration()) |
| return 0; |
| |
| assert(f->type->ty == Tfunction); |
| TypeFunction *tf = (TypeFunction *)f->type; |
| if (tf->isnothrow) |
| { |
| PURE purity = f->isPure(); |
| if (purity == PUREstrong) |
| return 2; |
| if (purity == PUREconst) |
| return 1; |
| } |
| return 0; |
| } |
| |
| int callSideEffectLevel(Type *t) |
| { |
| t = t->toBasetype(); |
| |
| TypeFunction *tf; |
| if (t->ty == Tdelegate) |
| tf = (TypeFunction *)((TypeDelegate *)t)->next; |
| else |
| { |
| assert(t->ty == Tfunction); |
| tf = (TypeFunction *)t; |
| } |
| |
| tf->purityLevel(); |
| PURE purity = tf->purity; |
| if (t->ty == Tdelegate && purity > PUREweak) |
| { |
| if (tf->isMutable()) |
| purity = PUREweak; |
| else if (!tf->isImmutable()) |
| purity = PUREconst; |
| } |
| |
| if (tf->isnothrow) |
| { |
| if (purity == PUREstrong) |
| return 2; |
| if (purity == PUREconst) |
| return 1; |
| } |
| return 0; |
| } |
| |
| bool lambdaHasSideEffect(Expression *e) |
| { |
| switch (e->op) |
| { |
| // Sort the cases by most frequently used first |
| case TOKassign: |
| case TOKplusplus: |
| case TOKminusminus: |
| case TOKdeclaration: |
| case TOKconstruct: |
| case TOKblit: |
| case TOKaddass: |
| case TOKminass: |
| case TOKcatass: |
| case TOKmulass: |
| case TOKdivass: |
| case TOKmodass: |
| case TOKshlass: |
| case TOKshrass: |
| case TOKushrass: |
| case TOKandass: |
| case TOKorass: |
| case TOKxorass: |
| case TOKpowass: |
| case TOKin: |
| case TOKremove: |
| case TOKassert: |
| case TOKhalt: |
| case TOKdelete: |
| case TOKnew: |
| case TOKnewanonclass: |
| return true; |
| |
| case TOKcall: |
| { |
| CallExp *ce = (CallExp *)e; |
| /* Calling a function or delegate that is pure nothrow |
| * has no side effects. |
| */ |
| if (ce->e1->type) |
| { |
| Type *t = ce->e1->type->toBasetype(); |
| if (t->ty == Tdelegate) |
| t = ((TypeDelegate *)t)->next; |
| if (t->ty == Tfunction && |
| (ce->f ? callSideEffectLevel(ce->f) |
| : callSideEffectLevel(ce->e1->type)) > 0) |
| { |
| } |
| else |
| return true; |
| } |
| break; |
| } |
| |
| case TOKcast: |
| { |
| CastExp *ce = (CastExp *)e; |
| /* if: |
| * cast(classtype)func() // because it may throw |
| */ |
| if (ce->to->ty == Tclass && ce->e1->op == TOKcall && ce->e1->type->ty == Tclass) |
| return true; |
| break; |
| } |
| |
| default: |
| break; |
| } |
| return false; |
| } |
| |
| |
| /*********************************** |
| * The result of this expression will be discarded. |
| * Print error messages if the operation has no side effects (and hence is meaningless). |
| * Returns: |
| * true if expression has no side effects |
| */ |
| bool discardValue(Expression *e) |
| { |
| if (lambdaHasSideEffect(e)) // check side-effect shallowly |
| return false; |
| switch (e->op) |
| { |
| case TOKcast: |
| { |
| CastExp *ce = (CastExp *)e; |
| if (ce->to->equals(Type::tvoid)) |
| { |
| /* |
| * Don't complain about an expression with no effect if it was cast to void |
| */ |
| return false; |
| } |
| break; // complain |
| } |
| |
| case TOKerror: |
| return false; |
| |
| case TOKvar: |
| { |
| VarDeclaration *v = ((VarExp *)e)->var->isVarDeclaration(); |
| if (v && (v->storage_class & STCtemp)) |
| { |
| // Bugzilla 5810: Don't complain about an internal generated variable. |
| return false; |
| } |
| break; |
| } |
| case TOKcall: |
| /* Issue 3882: */ |
| if (global.params.warnings != DIAGNOSTICoff && !global.gag) |
| { |
| CallExp *ce = (CallExp *)e; |
| if (e->type->ty == Tvoid) |
| { |
| /* Don't complain about calling void-returning functions with no side-effect, |
| * because purity and nothrow are inferred, and because some of the |
| * runtime library depends on it. Needs more investigation. |
| * |
| * One possible solution is to restrict this message to only be called in hierarchies that |
| * never call assert (and or not called from inside unittest blocks) |
| */ |
| } |
| else if (ce->e1->type) |
| { |
| Type *t = ce->e1->type->toBasetype(); |
| if (t->ty == Tdelegate) |
| t = ((TypeDelegate *)t)->next; |
| if (t->ty == Tfunction && |
| (ce->f ? callSideEffectLevel(ce->f) |
| : callSideEffectLevel(ce->e1->type)) > 0) |
| { |
| const char *s; |
| if (ce->f) |
| s = ce->f->toPrettyChars(); |
| else if (ce->e1->op == TOKstar) |
| { |
| // print 'fp' if ce->e1 is (*fp) |
| s = ((PtrExp *)ce->e1)->e1->toChars(); |
| } |
| else |
| s = ce->e1->toChars(); |
| |
| e->warning("calling %s without side effects discards return value of type %s, prepend a cast(void) if intentional", |
| s, e->type->toChars()); |
| } |
| } |
| } |
| return false; |
| |
| case TOKscope: |
| e->error("%s has no effect", e->toChars()); |
| return true; |
| |
| case TOKandand: |
| case TOKoror: |
| { |
| LogicalExp *aae = (LogicalExp *)e; |
| return discardValue(aae->e2); |
| } |
| |
| case TOKquestion: |
| { |
| CondExp *ce = (CondExp *)e; |
| |
| /* Bugzilla 6178 & 14089: Either CondExp::e1 or e2 may have |
| * redundant expression to make those types common. For example: |
| * |
| * struct S { this(int n); int v; alias v this; } |
| * S[int] aa; |
| * aa[1] = 0; |
| * |
| * The last assignment statement will be rewitten to: |
| * |
| * 1 in aa ? aa[1].value = 0 : (aa[1] = 0, aa[1].this(0)).value; |
| * |
| * The last DotVarExp is necessary to take assigned value. |
| * |
| * int value = (aa[1] = 0); // value = aa[1].value |
| * |
| * To avoid false error, discardValue() should be called only when |
| * the both tops of e1 and e2 have actually no side effects. |
| */ |
| if (!lambdaHasSideEffect(ce->e1) && |
| !lambdaHasSideEffect(ce->e2)) |
| { |
| return discardValue(ce->e1) | |
| discardValue(ce->e2); |
| } |
| return false; |
| } |
| |
| case TOKcomma: |
| { |
| CommaExp *ce = (CommaExp *)e; |
| /* Check for compiler-generated code of the form auto __tmp, e, __tmp; |
| * In such cases, only check e for side effect (it's OK for __tmp to have |
| * no side effect). |
| * See Bugzilla 4231 for discussion |
| */ |
| CommaExp *firstComma = ce; |
| while (firstComma->e1->op == TOKcomma) |
| firstComma = (CommaExp *)firstComma->e1; |
| if (firstComma->e1->op == TOKdeclaration && |
| ce->e2->op == TOKvar && |
| ((DeclarationExp *)firstComma->e1)->declaration == ((VarExp*)ce->e2)->var) |
| { |
| return false; |
| } |
| // Don't check e1 until we cast(void) the a,b code generation |
| //discardValue(ce->e1); |
| return discardValue(ce->e2); |
| } |
| |
| case TOKtuple: |
| /* Pass without complaint if any of the tuple elements have side effects. |
| * Ideally any tuple elements with no side effects should raise an error, |
| * this needs more investigation as to what is the right thing to do. |
| */ |
| if (!hasSideEffect(e)) |
| break; |
| return false; |
| |
| default: |
| break; |
| } |
| e->error("%s has no effect in expression (%s)", Token::toChars(e->op), e->toChars()); |
| return true; |
| } |
| |
| /************************************************** |
| * Build a temporary variable to copy the value of e into. |
| * Params: |
| * stc = storage classes will be added to the made temporary variable |
| * name = name for temporary variable |
| * e = original expression |
| * Returns: |
| * Newly created temporary variable. |
| */ |
| VarDeclaration *copyToTemp(StorageClass stc, const char *name, Expression *e) |
| { |
| assert(name && name[0] == '_' && name[1] == '_'); |
| Identifier *id = Identifier::generateId(name); |
| ExpInitializer *ez = new ExpInitializer(e->loc, e); |
| VarDeclaration *vd = new VarDeclaration(e->loc, e->type, id, ez); |
| vd->storage_class = stc; |
| vd->storage_class |= STCtemp; |
| vd->storage_class |= STCctfe; // temporary is always CTFEable |
| return vd; |
| } |
| |
| /************************************************** |
| * Build a temporary variable to extract e's evaluation, if e is not trivial. |
| * Params: |
| * sc = scope |
| * name = name for temporary variable |
| * e0 = a new side effect part will be appended to it. |
| * e = original expression |
| * alwaysCopy = if true, build new temporary variable even if e is trivial. |
| * Returns: |
| * When e is trivial and alwaysCopy == false, e itself is returned. |
| * Otherwise, a new VarExp is returned. |
| * Note: |
| * e's lvalue-ness will be handled well by STCref or STCrvalue. |
| */ |
| Expression *extractSideEffect(Scope *sc, const char *name, |
| Expression **e0, Expression *e, bool alwaysCopy = false) |
| { |
| if (!alwaysCopy && isTrivialExp(e)) |
| return e; |
| |
| VarDeclaration *vd = copyToTemp(0, name, e); |
| if (e->isLvalue()) |
| vd->storage_class |= STCref; |
| else |
| vd->storage_class |= STCrvalue; |
| |
| Expression *de = new DeclarationExp(vd->loc, vd); |
| Expression *ve = new VarExp(vd->loc, vd); |
| de = expressionSemantic(de, sc); |
| ve = expressionSemantic(ve, sc); |
| |
| *e0 = Expression::combine(*e0, de); |
| return ve; |
| } |
