Ofast deprecation clarifications

Following up on the RFC discussion, this is clarifying that the main purpose
and effect of the -Ofast deprecation is to discourage its usage and that
everything else is more or less open for discussion, e.g. there is no timeline
yet for removal.

Author: sjoerdmeijer

clang/docs/CommandGuide/clang.rst

@@ -429,8 +429,11 @@ Code Generation Options
 
     :option:`-Ofast` Enables all the optimizations from :option:`-O3` along
     with other aggressive optimizations that may violate strict compliance with
-    language standards. This is deprecated in favor of :option:`-O3`
-    in combination with :option:`-ffast-math`.
+    language standards. This is deprecated in Clang-19 and a warning is emitted
+    that :option:`-O3` in combination with :option:`-ffast-math` should be used
+    instead if the request for non-standard math behavior is intended. Thus, as
+    there is no timeline yet for removal, the aim is to discourage its usage
+    due to the compliance violating optimizations.
 
     :option:`-Os` Like :option:`-O2` with extra optimizations to reduce code
     size.

clang/docs/ReleaseNotes.rst

@@ -495,10 +495,12 @@ New Compiler Flags
 Deprecated Compiler Flags
 -------------------------
 
-- The ``-Ofast`` command-line option has been deprecated. This option both
-  enables the ``-O3`` optimization-level, as well as enabling non-standard
-  ``-ffast-math`` behaviors. As such, it is somewhat misleading as an
-  "optimization level". Users are advised to switch to ``-O3 -ffast-math`` if
+- The ``-Ofast`` command-line option has been deprecated, but there is no
+  timeline for removal yet. Thus, the main effect of emitting a deprecation
+  warning message is to discourage its usage due to the problems of ``-Ofast``:
+  it enables both the ``-O3`` optimization-level as well as non-standard
+  ``-ffast-math`` behaviors and as such it is perceived to be misleading as an
+  optimization level.  Users are advised to switch to ``-O3 -ffast-math`` if
   the use of non-standard math behavior is intended, and ``-O3`` otherwise.
   See `RFC <https://discourse.llvm.org/t/rfc-deprecate-ofast/78687>`_ for details.