[PATCH] D136160: [Attr][Doc] Fix pragma unroll documentation.

[Alexey Bader via Phabricator via cfe-commits]

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There is a contradiction in the #pragma unroll behavior documentation.
It says that specifying `#pragma unroll` without a parameter directs the
loop unroller to attempt to partially unroll the loop if the trip count
is not known at compile time. At the same time later it states that
`#pragma unroll` has identical semantics to `#pragma clang loop
unroll(full)`, which doesn't attempt to unroll partially if the trip
count is not known at compile time.

If unroll(enable) is specified the unroller will attempt to fully unroll the loop if the trip count is known at compile time. If the fully unrolled code size is greater than an internal limit the loop will be partially unrolled up to this limit. If the trip count is not known at compile time the loop will be partially unrolled with a heuristically chosen unroll factor.

If unroll(full) is specified the unroller will attempt to fully unroll the loop if the trip count is known at compile time identically to unroll(enable). However, with unroll(full) the loop will not be unrolled if the loop count is not known at compile time.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D136160

Files:
  clang/include/clang/Basic/AttrDocs.td


Index: clang/include/clang/Basic/AttrDocs.td
===================================================================
--- clang/include/clang/Basic/AttrDocs.td
+++ clang/include/clang/Basic/AttrDocs.td
@@ -3569,7 +3569,7 @@
   }
 
 ``#pragma unroll`` and ``#pragma unroll _value_`` have identical semantics to
-``#pragma clang loop unroll(full)`` and
+``#pragma clang loop unroll(enable)`` and
 ``#pragma clang loop unroll_count(_value_)`` respectively. ``#pragma nounroll``
 is equivalent to ``#pragma clang loop unroll(disable)``. See
 `language extensions


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