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90 lines
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90 lines
4.5 KiB
HTML
4 years ago
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<title>Gimplification pass - GNU Compiler Collection (GCC) Internals</title>
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<link rel="up" href="Passes.html#Passes" title="Passes">
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<link rel="prev" href="Cilk-Plus-Transformation.html#Cilk-Plus-Transformation" title="Cilk Plus Transformation">
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<link rel="next" href="Pass-manager.html#Pass-manager" title="Pass manager">
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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<body>
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<div class="node">
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<a name="Gimplification-pass"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Pass-manager.html#Pass-manager">Pass manager</a>,
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Previous: <a rel="previous" accesskey="p" href="Cilk-Plus-Transformation.html#Cilk-Plus-Transformation">Cilk Plus Transformation</a>,
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Up: <a rel="up" accesskey="u" href="Passes.html#Passes">Passes</a>
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<hr>
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</div>
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<h3 class="section">9.3 Gimplification pass</h3>
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<p><a name="index-gimplification-1684"></a><a name="index-GIMPLE-1685"></a><dfn>Gimplification</dfn> is a whimsical term for the process of converting
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the intermediate representation of a function into the GIMPLE language
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(see <a href="GIMPLE.html#GIMPLE">GIMPLE</a>). The term stuck, and so words like “gimplification”,
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“gimplify”, “gimplifier” and the like are sprinkled throughout this
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section of code.
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<p>While a front end may certainly choose to generate GIMPLE directly if
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it chooses, this can be a moderately complex process unless the
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intermediate language used by the front end is already fairly simple.
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Usually it is easier to generate GENERIC trees plus extensions
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and let the language-independent gimplifier do most of the work.
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<p><a name="index-gimplify_005ffunction_005ftree-1686"></a><a name="index-gimplify_005fexpr-1687"></a><a name="index-lang_005fhooks_002egimplify_005fexpr-1688"></a>The main entry point to this pass is <code>gimplify_function_tree</code>
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located in <samp><span class="file">gimplify.c</span></samp>. From here we process the entire
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function gimplifying each statement in turn. The main workhorse
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for this pass is <code>gimplify_expr</code>. Approximately everything
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passes through here at least once, and it is from here that we
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invoke the <code>lang_hooks.gimplify_expr</code> callback.
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<p>The callback should examine the expression in question and return
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<code>GS_UNHANDLED</code> if the expression is not a language specific
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construct that requires attention. Otherwise it should alter the
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expression in some way to such that forward progress is made toward
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producing valid GIMPLE. If the callback is certain that the
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transformation is complete and the expression is valid GIMPLE, it
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should return <code>GS_ALL_DONE</code>. Otherwise it should return
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<code>GS_OK</code>, which will cause the expression to be processed again.
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If the callback encounters an error during the transformation (because
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the front end is relying on the gimplification process to finish
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semantic checks), it should return <code>GS_ERROR</code>.
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</body></html>
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