From 692c9b459d6de7f6b4bb41361d6206598167ee05 Mon Sep 17 00:00:00 2001
From: Antoine Viallon <antoine@lesviallon.fr>
Date: Sun, 10 Apr 2022 22:34:18 +0200
Subject: [PATCH] [Packages] Improve compile options and document them

---
 packages.nix | 26 +++++++++++++++++++++-----
 1 file changed, 21 insertions(+), 5 deletions(-)

diff --git a/packages.nix b/packages.nix
index f468202..ba715f1 100644
--- a/packages.nix
+++ b/packages.nix
@@ -24,19 +24,35 @@ in
     compileFlags = mkOption {
       default = [
         "-O3" "-march=${generalCfg.cpuArch}" "-mtune=${generalCfg.cpuTune}"
-        "-feliminate-unused-debug-types" "--param=ssp-buffer-size=32"
-        # "-Wl,--copy-dt-needed-entries-m64-fasynchronous-unwind-tables"
-        "-fasynchronous-unwind-tables"
-        "-fno-semantic-interposition"
+        "-feliminate-unused-debug-types"
+        "--param=ssp-buffer-size=32"
+        
+        "-fno-asynchronous-unwind-tables"
+
+        # Fat LTO objects are object files that contain both the intermediate language and the object code. This makes them usable for both LTO linking and normal linking.
+        "-flto=auto" # Use -flto=auto to use GNU make’s job server, if available, or otherwise fall back to autodetection of the number of CPU threads present in your system.
         "-ffat-lto-objects"
+
+        # Math optimizations leading to loss of precision
         "-fno-signed-zeros"
         "-fno-trapping-math"
         "-fassociative-math"
-        "-fexceptions"
+
+        # Perform loop distribution of patterns that can be code generated with calls to a library (activated at O3 and more)
         "-ftree-loop-distribute-patterns"
+        
         "-Wl,-sort-common"
+
+        # The compiler assumes that if interposition happens for functions the overwriting function will have precisely the same semantics (and side effects)
         "-fno-semantic-interposition"
+        
+        # Perform interprocedural pointer analysis and interprocedural modification and reference analysis. This option can cause excessive memory and compile-time usage on large compilation units.
         "-fipa-pta"
+
+
+        "-fdevirtualize-speculatively"
+        
+        # Stream extra information needed for aggressive devirtualization when running the link-time optimizer in local transformation mode.
         "-fdevirtualize-at-ltrans"
         ];
       example = [ "-O2" "-mavx" ];