Honor -finline-functions and -finline-hint-functions at -O0

[davezarzycki]

Summary

This fixes a regression introduced (over three years ago!) by fcd33149b48885ab8e4ca4ffb6977bce5be2e623.

[lebedev.ri]

This clearly needs tests

[davezarzycki]

Hi @lebedev.ri – Before I add a small new test file, is there an existing one that you know of that would be good to extend?

[MaskRay]

Why you say regression, do you have a case where fcd33149b48885ab8e4ca4ffb6977bce5be2e623 actually regressed things?

-O0 implies optnone. For -Xclang -disable-O0-optnone -O0 -finline-functions, the patch can indeed make a difference. -disable-O0-optnone is currently a debug aid AFAICT.

GCC -O0 -finline-functions does not seem to have a difference.

clang/lib/Frontend/CompilerInvocation.cpp

702

The old order looks good. The new ordering does not seen to be needed? The assert is also unnecessary.

[davezarzycki]

Hi @MaskRay – I was just looking at the source history. I didn't test the old way. As it turns out there isn't a regression, but just some unexplained code in the current clang option parsing. And the -disable-O0-optnone is a useful hint. Thanks! I've been hacking on clang and trying to get the normal inliner pass to run at -O0, but with no luck so far.

[davezarzycki]

I'm abandoning this due to lack of time and the problem being more involved than I thought.

clang/lib/Frontend/CompilerInvocation.cpp

static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
   }
   Opts.OptimizationLevel = OptimizationLevel;
 
   // At O0 we want to fully disable inlining outside of cases marked with
   // 'alwaysinline' that are required for correctness.
   Opts.setInlining((Opts.OptimizationLevel == 0)
                        ? CodeGenOptions::OnlyAlwaysInlining
                        : CodeGenOptions::NormalInlining);
-  // Explicit inlining flags can disable some or all inlining even at
-  // optimization levels above zero.
+  // Handle inlining overrides
   if (Arg *InlineArg = Args.getLastArg(
           options::OPT_finline_functions, options::OPT_finline_hint_functions,
           options::OPT_fno_inline_functions, options::OPT_fno_inline)) {
-    if (Opts.OptimizationLevel > 0) {
-      const Option &InlineOpt = InlineArg->getOption();
-      if (InlineOpt.matches(options::OPT_finline_functions))
-        Opts.setInlining(CodeGenOptions::NormalInlining);
-      else if (InlineOpt.matches(options::OPT_finline_hint_functions))
-        Opts.setInlining(CodeGenOptions::OnlyHintInlining);
-      else
-        Opts.setInlining(CodeGenOptions::OnlyAlwaysInlining);
+    if (InlineOpt.matches(options::OPT_fno_inline)) {
+      Opts.setInlining(CodeGenOptions::OnlyAlwaysInlining);
+    } else if (InlineOpt.matches(options::OPT_fno_inline_functions)) {
+    } else if (InlineOpt.matches(options::OPT_finline_functions)) {
+      Opts.setInlining(CodeGenOptions::NormalInlining);
+    } else {
+      assert(InlineOpt.matches(options::OPT_finline_hint_functions) &&
+             "Option parsing bug");
+      Opts.setInlining(Args.hasArg(OPT_finline_functions)
+                           ? CodeGenOptions::NormalInlining
+                           : CodeGenOptions::OnlyHintInlining);
     }
   }
 
   Opts.ExperimentalNewPassManager = Args.hasFlag(
       OPT_fexperimental_new_pass_manager, OPT_fno_experimental_new_pass_manager,
       /* Default */ ENABLE_EXPERIMENTAL_NEW_PASS_MANAGER);
 
   Opts.DebugPassManager =