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# dmd.sideeffect

Find side-effects of expressions.
Authors:
Walter Bright
License:
Boost License 1.0

Source sideeffect.d

Documentation https://dlang.org/phobos/dmd_sideeffect.html

Coverage https://codecov.io/gh/dlang/dmd/src/master/src/dmd/sideeffect.d

bool `isTrivialExp`(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 `hasSideEffect`(Expression `e`);
  Determine if Expression has any side effects.
int `callSideEffectLevel`(FuncDeclaration `f`);
  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
bool `discardValue`(Expression `e`);
  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
VarDeclaration `copyToTemp`(StorageClass `stc`, const char[] `name`, Expression `e`);
  Build a temporary variable to copy the value of e into.
  Parameters:

  StorageClass `stc` | storage classes will be added to the made temporary variable
  char[] `name` | name for temporary variable
  Expression `e` | original expression

  Returns:
  Newly created temporary variable.
Expression `extractSideEffect`(Scope* `sc`, const char[] `name`, ref Expression `e0`, Expression `e`, bool `alwaysCopy` = false);
  Build a temporary variable to extract e's evaluation, if e is not trivial.
  Parameters:

  Scope* `sc` | scope
  char[] `name` | name for temporary variable
  Expression `e0` | a new side effect part will be appended to it.
  Expression `e` | original expression
  bool `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 STC.ref_ or STC.rvalue.

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