Bug 1368649 - Default to -O2 when building on Linux without PGO. r=gps

-Os generates smaller code, at the expense of performance. On desktop,
this tradeoff is not necessarily the best, especially when considering
the vast performance difference. Most downstream redistributors also
don't do PGO and don't override defaults, so they would tend to ship
slower builds as a consequence.

We however keep -Os as default for debug builds for now, because -O2
triggers -Werror=strict-overflow failures somehow.

--HG--
extra : rebase_source : ad2f4fedb7934b6b23b84412c86b30d29a8fb5f8

build/moz.configure/warnings.configure

@@ -98,8 +98,8 @@ check_and_add_gcc_warning('-Wno-error=array-bounds')
 # can't get rid of those PGO warnings
 check_and_add_gcc_warning('-Wno-error=coverage-mismatch', when='MOZ_PGO')
 
-# false positives during PGO
-check_and_add_gcc_warning('-Wno-error=free-nonheap-object', when='MOZ_PGO')
+# false positives depending on optimizations
+check_and_add_gcc_warning('-Wno-error=free-nonheap-object')
 
 # catches format/argument mismatches with printf
 check_and_add_gcc_warning('-Wformat')

old-configure.in

@@ -888,7 +888,11 @@ case "$target" in
 *-*linux*)
     if test "$GNU_CC" -o "$GNU_CXX"; then
         MOZ_PGO_OPTIMIZE_FLAGS="-O3"
-        MOZ_OPTIMIZE_FLAGS="-Os"
+        if test -n "$MOZ_DEBUG"; then
+            MOZ_OPTIMIZE_FLAGS="-Os"
+        else
+            MOZ_OPTIMIZE_FLAGS="-O2"
+        fi
         if test -z "$CLANG_CC"; then
            MOZ_OPTIMIZE_FLAGS="-freorder-blocks $MOZ_OPTIMIZE_FLAGS"
         fi