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improve some of the documentation around target data layout strings.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141733 91177308-0d34-0410-b5e6-96231b3b80d8
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@@ -1406,6 +1406,22 @@ target datalayout = "<i>layout specification</i>"
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implemented in terms of 64 <2 x double>, for example.</li>
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</ol>
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<p>The function of the data layout string may not be what you expect. Notably,
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this is not a specification from the frontend of what alignment the code
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generator should use.</p>
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<p>Instead, if specified, the target data layout is required to match what the
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ultimate <em>code generator</em> expects. This string is used by the
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mid-level optimizers to
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improve code, and this only works if it matches what the ultimate code
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generator uses. If you would like to generate IR that does not embed this
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target-specific detail into the IR, then you don't have to specify the
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string. This will disable some optimizations that require precise layout
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information, but this also prevents those optimizations from introducing
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target specificity into the IR.</p>
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</div>
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