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diff -up firefox-55.0/js/src/old-configure.in.rhbz-1219542-s390 firefox-55.0/js/src/old-configure.in
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--- firefox-55.0/js/src/old-configure.in.rhbz-1219542-s390	2017-07-31 18:20:48.000000000 +0200
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+++ firefox-55.0/js/src/old-configure.in	2017-08-02 14:31:32.190243669 +0200
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@@ -541,7 +541,7 @@ case "$host" in
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 *-linux*|*-kfreebsd*-gnu|*-gnu*)
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     HOST_CFLAGS="$HOST_CFLAGS -DXP_UNIX"
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-    HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O3}"
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+    HOST_OPTIMIZE_FLAGS="${HOST_OPTIMIZE_FLAGS=-O1}"
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     ;;
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 *)
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@@ -617,8 +617,8 @@ case "$target" in
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 *-*linux*)
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     if test "$GNU_CC" -o "$GNU_CXX"; then
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-        MOZ_PGO_OPTIMIZE_FLAGS="-O3"
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-        MOZ_OPTIMIZE_FLAGS="-O3"
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+        MOZ_PGO_OPTIMIZE_FLAGS="-O1"
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+        MOZ_OPTIMIZE_FLAGS="-O1"
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         if test -z "$CLANG_CC"; then
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            MOZ_OPTIMIZE_FLAGS="-freorder-blocks $MOZ_OPTIMIZE_FLAGS"
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         fi