From 989e5df1ebe58684d9950f1ee041b20d7224a85d Mon Sep 17 00:00:00 2001
From: Moritz Bunkus <moritz@bunkus.org>
Date: Fri, 17 Nov 2017 21:57:32 +0100
Subject: [PATCH] configure: use `-O3` with clang++ 3.8.0 or newer

Older versions suffered from excessive memory usage with optimization
levels higher than `-O1`:

%https://bugs.llvm.org/show_bug.cgi?id=11962

v3.8.0 is known to be OK, though.
---
 NEWS.md                   | 4 ++++
 ac/debugging_profiling.m4 | 2 +-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/NEWS.md b/NEWS.md
index 343005b30..774b675d2 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -13,6 +13,10 @@
   removed during code refactoring in release v15.0.0.
 * mkvmerge: AVC & HEVC ES parsers: performance improvements by copying much
   less memory around.
+* build system: when building with clang v3.8.0 or newer, `configure` will no
+  longer restrict optimization flags to `-O1` and use `-O3` again (older
+  versions of clang suffered from excessive memory usage with higher
+  optimization levels).
 
 ## Bug fixes
 
diff --git a/ac/debugging_profiling.m4 b/ac/debugging_profiling.m4
index 5dd66845a..3aaabdc75 100644
--- a/ac/debugging_profiling.m4
+++ b/ac/debugging_profiling.m4
@@ -34,7 +34,7 @@ else
 fi
 
 if test x"$enable_optimization" = xyes; then
-  if test x"$ac_cv_compiler_is_clang" = xyes; then
+  if test x"$ac_cv_compiler_is_clang" = xyes && ! check_version 3.8.0 $ac_cv_compiler_version; then
     opt_features_no="$opt_features_no\n   * full optimization: due to bug 11962 in LLVM/clang only -O1 will be used for optimization"
     OPTIMIZATION_CFLAGS="-O1"