Remove -mrelax-all from Clang -O0

[dberris]

Summary

Remove the -mrelax-all options passed onto the integrated assembler in -O0.

The -mrelax-all option causes short jumps emitted when lowering to be widened unconditionally. For cases where we need control of the length of the jump instruction (i.e. to make the jump instructions short) when lowering, -mrelax-all causes them all to be lengthened instead of relying on the instruction layout algorithms to make the decision appropriately.

[cfe-commits]

We need to benchmark this to see if it still makes a difference.

My canonical test is the .s of a lto of clang.

Cheers,
Rafael

[majnemer]

Why are you making this change? I cannot see a justification in the description.

[dberris]

Changed the description to provide a justification.

lib/Driver/Tools.cpp

 static bool ShouldDisableDwarfDirectory(const ArgList &Args,
                                         const ToolChain &TC) {
   bool UseDwarfDirectory =
       Args.hasFlag(options::OPT_fdwarf_directory_asm,
                    options::OPT_fno_dwarf_directory_asm, TC.useIntegratedAs());
   return !UseDwarfDirectory;
 }
 
-/// \brief Check whether the given input tree contains any compilation actions.
-static bool ContainsCompileAction(const Action *A) {
-  if (isa<CompileJobAction>(A) || isa<BackendJobAction>(A))
-    return true;
-
-  for (const auto &AI : A->inputs())
-    if (ContainsCompileAction(AI))
-      return true;
-
-  return false;
-}
-
 /// \brief Check if -relax-all should be passed to the internal assembler.
-/// This is done by default when compiling non-assembler source with -O0.
 static bool UseRelaxAll(Compilation &C, const ArgList &Args) {
-  bool RelaxDefault = true;
-
-  if (Arg *A = Args.getLastArg(options::OPT_O_Group))
-    RelaxDefault = A->getOption().matches(options::OPT_O0);
-
-  if (RelaxDefault) {
-    RelaxDefault = false;
-    for (const auto &Act : C.getActions()) {
-      if (ContainsCompileAction(Act)) {
-        RelaxDefault = true;
-        break;
-      }
-    }
-  }
-
   return Args.hasFlag(options::OPT_mrelax_all, options::OPT_mno_relax_all,
-                      RelaxDefault);
+                      false);
 }
 
 // Convert an arg of the form "-gN" or "-ggdbN" or one of their aliases
 // to the corresponding DebugInfoKind.
 static codegenoptions::DebugInfoKind DebugLevelToInfoKind(const Arg &A) {
   assert(A.getOption().matches(options::OPT_gN_Group) &&
          "Not a -g option that specifies a debug-info level");
   if (A.getOption().matches(options::OPT_g0) ||

test/Driver/integrated-as.c

 // RUN: %clang -### -c -save-temps -integrated-as %s 2>&1 | FileCheck %s
 
 // CHECK: cc1as
-// CHECK: -mrelax-all
 
 // RUN: %clang -### -fintegrated-as -c -save-temps %s 2>&1 | FileCheck %s -check-prefix FIAS
 
 // FIAS: cc1as
 
 // RUN: %clang -### -fno-integrated-as -S %s 2>&1 \
 // RUN:     | FileCheck %s -check-prefix NOFIAS
 
 // NOFIAS-NOT: cc1as
 // NOFIAS: -cc1
 // NOFIAS: -no-integrated-as