[llvm-branch-commits] [llvm-branch] r367997 - Merging r367941:

[Hans Wennborg via llvm-branch-commits]

Author: hans
Date: Tue Aug  6 01:30:56 2019
New Revision: 367997

URL: http://llvm.org/viewvc/llvm-project?rev=367997&view=rev
Log:
Merging r367941:
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r367941 | reames | 2019-08-06 00:34:59 +0200 (Tue, 06 Aug 2019) | 5 lines

Add a note to the release not about a potentially breaking optimization

This has come up twice already (once in pr42763 and once in the commit thread), so give warning of a new way in which UB can result in unexpected program behavior.


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Modified:
    llvm/branches/release_90/   (props changed)
    llvm/branches/release_90/docs/ReleaseNotes.rst

Propchange: llvm/branches/release_90/
------------------------------------------------------------------------------
--- svn:mergeinfo (original)
+++ svn:mergeinfo Tue Aug  6 01:30:56 2019
@@ -1,3 +1,3 @@
 /llvm/branches/Apple/Pertwee:110850,110961
 /llvm/branches/type-system-rewrite:133420-134817
-/llvm/trunk:155241,366431,366481,366487,366527,366570,366660,366868,366925,367030,367062,367124,367215,367292,367304,367306,367314,367340-367341,367394,367396,367398,367417,367662,367753,367846-367847
+/llvm/trunk:155241,366431,366481,366487,366527,366570,366660,366868,366925,367030,367062,367124,367215,367292,367304,367306,367314,367340-367341,367394,367396,367398,367417,367662,367753,367846-367847,367941

Modified: llvm/branches/release_90/docs/ReleaseNotes.rst
URL: http://llvm.org/viewvc/llvm-project/llvm/branches/release_90/docs/ReleaseNotes.rst?rev=367997&r1=367996&r2=367997&view=diff
==============================================================================
--- llvm/branches/release_90/docs/ReleaseNotes.rst (original)
+++ llvm/branches/release_90/docs/ReleaseNotes.rst Tue Aug  6 01:30:56 2019
@@ -62,6 +62,19 @@ Non-comprehensive list of changes in thi
 
    Makes programs 10x faster by doing Special New Thing.
 
+Noteworthy optimizations
+------------------------
+
+* LLVM will now remove stores to constant memory (since this is a
+  contradiction) under the assumption the code in question must be dead.  This
+  has proven to be problematic for some C/C++ code bases which expect to be
+  able to cast away 'const'.  This is (and has always been) undefined
+  behavior, but up until now had not been actively utilized for optimization
+  purposes in this exact way.  For more information, please see:
+  `bug 42763 <https://bugs.llvm.org/show_bug.cgi?id=42763>_` and
+  `post commit discussion <http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20190422/646945.html>_`.  
+
+
 Changes to the LLVM IR
 ----------------------