Do not use -Ofast

-Ofast implies -funsafe-math-optimizations, which affects the global FP state
for all programs: when used at link time, it may include libraries or startup
files that change the default FPU control word or other similar optimizations.

-Ofast enables (directly or indirectly):
  - ❌ -fallow-store-data-races
  - ✔ -fno-semantic-interposition
  - ✔ -fno-math-errno
  - ❌ -funsafe-math-optimizations
  - ❌ -ffinite-math-only
  - ✔ -fno-rounding-math (_default_)
  - ✔ -fno-signaling-nans (_default_)
  - ❔ -fcx-limited-range
  - ✔ -fexcess-precision=fast
  - ✔ -fno-signed-zeros
  - ✔ -fno-trapping-math
  - ✔ -fassociative-math
  - ❌ -freciprocal-math (disabled in #8280)

We should not use -fallow-store-data-races, -ffinite-math-only.

We should not use -funsafe-math-optimizations at link time, as it affects the
global FP state. It's probably easier to replace it with the individual options
-fno-signed-zeros, -fno-trapping-math and -fassociative-math.

We may revisit -fcx-limited-range if we do use Complex arithmetics.

-freciprocal-math was already disabled explicitly, see #8280.

Author: fwyzard

scram-tools.file/tools/gcc/ofast-flag.xml

@@ -1,12 +1,24 @@
-  <tool name="ofast-flag" version="1.0" revision="1">
-    <flags CXXFLAGS="-Ofast -fno-reciprocal-math"/>
-    <ifarch match="ppc64le|amd64|x86_64">
-      <flags CXXFLAGS="-mrecip=none"/>
-    </ifarch>
-    <ifarchitecture name="slc6_">
-      <ifcompiler name="llvm">
-        <flags CXXFLAGS="-fno-builtin"/>
-      </ifcompiler>
-    </ifarchitecture>
-    <flags NO_RECURSIVE_EXPORT="1"/>
-  </tool>
+<tool name="ofast-flag" version="2.0" revision="1">
+  <!--
+  As of GCC version 13.3.0, `-Ofast` enables (directly or indirectly):
+    - `-fallow-store-data-races`
+    - `-fno-semantic-interposition`
+    - `-fno-math-errno`
+    - `-funsafe-math-optimizations`
+    - `-ffinite-math-only`
+    - `-fno-rounding-math` (enabled by default)
+    - `-fno-signaling-nans` (enabled by default)
+    - `-fcx-limited-range`
+    - `-fexcess-precision=fast`
+    - `-fno-signed-zeros`
+    - `-fno-trapping-math`
+    - `-fassociative-math`
+    - `-freciprocal-math` (disabled in cms-sw/cmsdist#8280)
+  We disable `-fallow-store-data-races`, `-funsafe-math-optimizations`, `-ffinite-math-only` and `-freciprocal-math` (see cms-sw/cmsdist#8280).
+  -->
+  <flags CXXFLAGS="-fno-semantic-interposition -fno-math-errno -fno-rounding-math -fno-signaling-nans -fexcess-precision=fast -fno-signed-zeros -fno-trapping-math -fassociative-math -fno-reciprocal-math"/>
+  <ifarch match="ppc64le|amd64|x86_64">
+    <flags CXXFLAGS="-mrecip=none"/>
+  </ifarch>
+  <flags NO_RECURSIVE_EXPORT="1"/>
+</tool>