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<head>
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<title>Logical Operators (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Logical Operators (GNU Compiler Collection (GCC) Internals)">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Operands.html#Operands" rel="up" title="Operands">
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<link href="Manipulating-GIMPLE-statements.html#Manipulating-GIMPLE-statements" rel="next" title="Manipulating GIMPLE statements">
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<link href="Conditional-Expressions.html#Conditional-Expressions" rel="prev" title="Conditional Expressions">
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</head>
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<body lang="en">
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<a name="Logical-Operators"></a>
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<div class="header">
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<p>
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Previous: <a href="Conditional-Expressions.html#Conditional-Expressions" accesskey="p" rel="prev">Conditional Expressions</a>, Up: <a href="Operands.html#Operands" accesskey="u" rel="up">Operands</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Logical-Operators-1"></a>
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<h4 class="subsection">12.6.4 Logical Operators</h4>
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<a name="index-Logical-Operators"></a>
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<p>Except when they appear in the condition operand of a
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<code>GIMPLE_COND</code>, logical ‘and’ and ‘or’ operators are simplified
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as follows: <code>a = b && c</code> becomes
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</p>
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<div class="smallexample">
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<pre class="smallexample">T1 = (bool)b;
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if (T1 == true)
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T1 = (bool)c;
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a = T1;
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</pre></div>
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<p>Note that <code>T1</code> in this example cannot be an expression temporary,
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because it has two different assignments.
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</p>
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<a name="Manipulating-operands"></a>
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<h4 class="subsection">12.6.5 Manipulating operands</h4>
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<p>All gimple operands are of type <code>tree</code>. But only certain
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types of trees are allowed to be used as operand tuples. Basic
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validation is controlled by the function
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<code>get_gimple_rhs_class</code>, which given a tree code, returns an
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<code>enum</code> with the following values of type <code>enum
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gimple_rhs_class</code>
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</p>
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<ul>
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<li> <code>GIMPLE_INVALID_RHS</code>
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The tree cannot be used as a GIMPLE operand.
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</li><li> <code>GIMPLE_TERNARY_RHS</code>
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The tree is a valid GIMPLE ternary operation.
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</li><li> <code>GIMPLE_BINARY_RHS</code>
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The tree is a valid GIMPLE binary operation.
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</li><li> <code>GIMPLE_UNARY_RHS</code>
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The tree is a valid GIMPLE unary operation.
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</li><li> <code>GIMPLE_SINGLE_RHS</code>
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The tree is a single object, that cannot be split into simpler
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operands (for instance, <code>SSA_NAME</code>, <code>VAR_DECL</code>, <code>COMPONENT_REF</code>, etc).
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<p>This operand class also acts as an escape hatch for tree nodes
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that may be flattened out into the operand vector, but would need
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more than two slots on the RHS. For instance, a <code>COND_EXPR</code>
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expression of the form <code>(a op b) ? x : y</code> could be flattened
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out on the operand vector using 4 slots, but it would also
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require additional processing to distinguish <code>c = a op b</code>
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from <code>c = a op b ? x : y</code>. Something similar occurs with
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<code>ASSERT_EXPR</code>. In time, these special case tree
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expressions should be flattened into the operand vector.
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</p></li></ul>
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<p>For tree nodes in the categories <code>GIMPLE_TERNARY_RHS</code>,
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<code>GIMPLE_BINARY_RHS</code> and <code>GIMPLE_UNARY_RHS</code>, they cannot be
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stored inside tuples directly. They first need to be flattened and
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separated into individual components. For instance, given the GENERIC
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expression
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</p>
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<div class="smallexample">
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<pre class="smallexample">a = b + c
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</pre></div>
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<p>its tree representation is:
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</p>
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<div class="smallexample">
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<pre class="smallexample">MODIFY_EXPR <VAR_DECL <a>, PLUS_EXPR <VAR_DECL <b>, VAR_DECL <c>>>
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</pre></div>
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<p>In this case, the GIMPLE form for this statement is logically
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identical to its GENERIC form but in GIMPLE, the <code>PLUS_EXPR</code>
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on the RHS of the assignment is not represented as a tree,
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instead the two operands are taken out of the <code>PLUS_EXPR</code> sub-tree
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and flattened into the GIMPLE tuple as follows:
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</p>
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<div class="smallexample">
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<pre class="smallexample">GIMPLE_ASSIGN <PLUS_EXPR, VAR_DECL <a>, VAR_DECL <b>, VAR_DECL <c>>
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</pre></div>
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<a name="Operand-vector-allocation"></a>
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<h4 class="subsection">12.6.6 Operand vector allocation</h4>
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<p>The operand vector is stored at the bottom of the three tuple
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structures that accept operands. This means, that depending on
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the code of a given statement, its operand vector will be at
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different offsets from the base of the structure. To access
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tuple operands use the following accessors
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</p>
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<dl>
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<dt><a name="index-gimple_005fnum_005fops"></a>GIMPLE function: <em>unsigned</em> <strong>gimple_num_ops</strong> <em>(gimple g)</em></dt>
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<dd><p>Returns the number of operands in statement G.
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</p></dd></dl>
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<dl>
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<dt><a name="index-gimple_005fop"></a>GIMPLE function: <em>tree</em> <strong>gimple_op</strong> <em>(gimple g, unsigned i)</em></dt>
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<dd><p>Returns operand <code>I</code> from statement <code>G</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-gimple_005fops"></a>GIMPLE function: <em>tree *</em> <strong>gimple_ops</strong> <em>(gimple g)</em></dt>
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<dd><p>Returns a pointer into the operand vector for statement <code>G</code>. This
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is computed using an internal table called <code>gimple_ops_offset_</code>[].
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This table is indexed by the gimple code of <code>G</code>.
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</p>
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<p>When the compiler is built, this table is filled-in using the
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sizes of the structures used by each statement code defined in
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gimple.def. Since the operand vector is at the bottom of the
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structure, for a gimple code <code>C</code> the offset is computed as sizeof
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(struct-of <code>C</code>) - sizeof (tree).
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</p>
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<p>This mechanism adds one memory indirection to every access when
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using <code>gimple_op</code>(), if this becomes a bottleneck, a pass can
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choose to memoize the result from <code>gimple_ops</code>() and use that to
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access the operands.
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</p></dd></dl>
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<a name="Operand-validation"></a>
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<h4 class="subsection">12.6.7 Operand validation</h4>
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<p>When adding a new operand to a gimple statement, the operand will
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be validated according to what each tuple accepts in its operand
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vector. These predicates are called by the
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<code>gimple_<var>name</var>_set_...()</code>. Each tuple will use one of the
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following predicates (Note, this list is not exhaustive):
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</p>
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<dl>
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<dt><a name="index-is_005fgimple_005fval"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_val</strong> <em>(tree t)</em></dt>
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<dd><p>Returns true if t is a "GIMPLE value", which are all the
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non-addressable stack variables (variables for which
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<code>is_gimple_reg</code> returns true) and constants (expressions for which
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<code>is_gimple_min_invariant</code> returns true).
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</p></dd></dl>
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<dl>
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<dt><a name="index-is_005fgimple_005faddressable"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_addressable</strong> <em>(tree t)</em></dt>
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<dd><p>Returns true if t is a symbol or memory reference whose address
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can be taken.
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</p></dd></dl>
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<dl>
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<dt><a name="index-is_005fgimple_005fasm_005fval"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_asm_val</strong> <em>(tree t)</em></dt>
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<dd><p>Similar to <code>is_gimple_val</code> but it also accepts hard registers.
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</p></dd></dl>
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<dl>
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<dt><a name="index-is_005fgimple_005fcall_005faddr"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_call_addr</strong> <em>(tree t)</em></dt>
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<dd><p>Return true if t is a valid expression to use as the function
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called by a <code>GIMPLE_CALL</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-is_005fgimple_005fmem_005fref_005faddr"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_mem_ref_addr</strong> <em>(tree t)</em></dt>
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<dd><p>Return true if t is a valid expression to use as first operand
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of a <code>MEM_REF</code> expression.
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</p></dd></dl>
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<dl>
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<dt><a name="index-is_005fgimple_005fconstant"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_constant</strong> <em>(tree t)</em></dt>
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<dd><p>Return true if t is a valid gimple constant.
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</p></dd></dl>
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<dl>
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<dt><a name="index-is_005fgimple_005fmin_005finvariant"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_min_invariant</strong> <em>(tree t)</em></dt>
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<dd><p>Return true if t is a valid minimal invariant. This is different
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from constants, in that the specific value of t may not be known
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at compile time, but it is known that it doesn’t change (e.g.,
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the address of a function local variable).
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</p></dd></dl>
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<dl>
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<dt><a name="index-is_005fgimple_005fip_005finvariant"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_ip_invariant</strong> <em>(tree t)</em></dt>
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<dd><p>Return true if t is an interprocedural invariant. This means that t
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is a valid invariant in all functions (e.g. it can be an address of a
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global variable but not of a local one).
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</p></dd></dl>
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<dl>
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<dt><a name="index-is_005fgimple_005fip_005finvariant_005faddress"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_ip_invariant_address</strong> <em>(tree t)</em></dt>
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<dd><p>Return true if t is an <code>ADDR_EXPR</code> that does not change once the
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program is running (and which is valid in all functions).
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</p></dd></dl>
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<a name="Statement-validation"></a>
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<h4 class="subsection">12.6.8 Statement validation</h4>
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<dl>
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<dt><a name="index-is_005fgimple_005fassign"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_assign</strong> <em>(gimple g)</em></dt>
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<dd><p>Return true if the code of g is <code>GIMPLE_ASSIGN</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-is_005fgimple_005fcall"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_call</strong> <em>(gimple g)</em></dt>
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<dd><p>Return true if the code of g is <code>GIMPLE_CALL</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-is_005fgimple_005fdebug"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_debug</strong> <em>(gimple g)</em></dt>
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<dd><p>Return true if the code of g is <code>GIMPLE_DEBUG</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-gimple_005fassign_005fcast_005fp"></a>GIMPLE function: <em>bool</em> <strong>gimple_assign_cast_p</strong> <em>(const_gimple g)</em></dt>
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<dd><p>Return true if g is a <code>GIMPLE_ASSIGN</code> that performs a type cast
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operation.
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</p></dd></dl>
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<dl>
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<dt><a name="index-gimple_005fdebug_005fbind_005fp"></a>GIMPLE function: <em>bool</em> <strong>gimple_debug_bind_p</strong> <em>(gimple g)</em></dt>
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<dd><p>Return true if g is a <code>GIMPLE_DEBUG</code> that binds the value of an
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expression to a variable.
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</p></dd></dl>
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<dl>
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<dt><a name="index-is_005fgimple_005fomp"></a>GIMPLE function: <em>bool</em> <strong>is_gimple_omp</strong> <em>(gimple g)</em></dt>
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<dd><p>Return true if g is any of the OpenMP codes.
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</p></dd></dl>
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<dl>
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<dt><a name="index-_0028gimple"></a>GIMPLE function: <em>gimple_debug_begin_stmt_p</em> <strong>(gimple</strong> <em>g)</em></dt>
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<dd><p>Return true if g is a <code>GIMPLE_DEBUG</code> that marks the beginning of
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a source statement.
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</p></dd></dl>
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<dl>
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<dt><a name="index-_0028gimple-1"></a>GIMPLE function: <em>gimple_debug_inline_entry_p</em> <strong>(gimple</strong> <em>g)</em></dt>
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<dd><p>Return true if g is a <code>GIMPLE_DEBUG</code> that marks the entry
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point of an inlined function.
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</p></dd></dl>
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<dl>
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<dt><a name="index-_0028gimple-2"></a>GIMPLE function: <em>gimple_debug_nonbind_marker_p</em> <strong>(gimple</strong> <em>g)</em></dt>
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<dd><p>Return true if g is a <code>GIMPLE_DEBUG</code> that marks a program location,
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without any variable binding.
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</p></dd></dl>
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<hr>
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<div class="header">
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<p>
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Previous: <a href="Conditional-Expressions.html#Conditional-Expressions" accesskey="p" rel="prev">Conditional Expressions</a>, Up: <a href="Operands.html#Operands" accesskey="u" rel="up">Operands</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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