[clang][PS4] Enable SplitLTOUnits by default

[ormris]

Summary

This patch contains the parts of the unified LTO pipeline specific to PS4/5. See this conversation: https://discourse.llvm.org/t/rfc-a-unified-lto-bitcode-frontend/61774/15

[MaskRay]

If a vendor wants to change some driver default, that's fine, especially when on/off already has a condition. But please include full context per https://llvm.org/docs/Phabricator.html#requesting-a-review-via-the-web-interface and add a clang/test/Driver/ test.
Also, "SIE" isn't a clear abbreviation. PS4 seems more understandable by other contributors.

[ormris]

Add context.

[ormris]

Changelog:

• Rebased
• Add tests

[ormris]

Attempt to fix pre-merge checks

[ormris]

clang-format

[probinson]

clang/test/Driver/split-lto-unit.c

9 ↗

(On Diff #526179)

This all shows that -funified-lto has the desired effect, but not what the defaults are (yes for PS4, no for e.g. linux).

[ormris]

• Unified LTO default for all PlayStation targets
• Add default case to tests
• SplitLTOUnit not default for PS4

clang/test/Driver/split-lto-unit.c

9 ↗

(On Diff #526179)

Should be fixed.

[probinson]

LGTM

[ormris]

Thanks!

clang/lib/Driver/ToolChains/Clang.cpp

void Clang::ConstructJob(Compilation &C, const JobAction &JA,
 
   // FIXME: Subclass ToolChain for SPIR and move this to addClangWarningOptions.
   if (Triple.isSPIR() || Triple.isSPIRV())
     CmdArgs.push_back("-Wspir-compat");
 
   // Select the appropriate action.
   RewriteKind rewriteKind = RK_None;
 
+  bool DefaultUnified = Triple.isPS4();
   bool UnifiedLTO =
           Args.hasFlag(options::OPT_funified_lto,
                        options::OPT_fno_unified_lto,
-                       false);
+                       DefaultUnified);
   if (UnifiedLTO)
     CmdArgs.push_back("-funified-lto");
 
   // If CollectArgsForIntegratedAssembler() isn't called below, claim the args
   // it claims when not running an assembler. Otherwise, clang would emit
   // "argument unused" warnings for assembler flags when e.g. adding "-E" to
   // flags while debugging something. That'd be somewhat inconvenient, and it's
   // also inconsistent with most other flags -- we don't warn on
if (WholeProgramVTables) {
 
     // Propagate -fwhole-program-vtables if this is an LTO compile.
     if (IsUsingLTO)
       CmdArgs.push_back("-fwhole-program-vtables");
   }
 
   bool DefaultsSplitLTOUnit =
       (WholeProgramVTables || SanitizeArgs.needsLTO()) &&
-      (LTOMode == LTOK_Full || TC.canSplitThinLTOUnit());
+      (LTOMode == LTOK_Full || TC.canSplitThinLTOUnit()) ||
+       UnifiedLTO;
   bool SplitLTOUnit =
       Args.hasFlag(options::OPT_fsplit_lto_unit,
                    options::OPT_fno_split_lto_unit, DefaultsSplitLTOUnit);
   if (SanitizeArgs.needsLTO() && !SplitLTOUnit)
     D.Diag(diag::err_drv_argument_not_allowed_with) << "-fno-split-lto-unit"
                                                     << "-fsanitize=cfi";
   if (SplitLTOUnit)
     CmdArgs.push_back("-fsplit-lto-unit");

clang/lib/Frontend/CompilerInvocation.cpp

if (Arg *A = Args.getLastArg(OPT_flto_EQ)) {
     Opts.PrepareForLTO = true;
     StringRef S = A->getValue();
     if (S == "thin")
       Opts.PrepareForThinLTO = true;
     else if (S != "full")
       Diags.Report(diag::err_drv_invalid_value) << A->getAsString(Args) << S;
   }
 
+  if (Opts.UnifiedLTO) {
+    if (T.getOS() == llvm::Triple::PS4)
+      Opts.EnableSplitLTOUnit = false;
+    else
+      Opts.EnableSplitLTOUnit = true;
+  }
+
   if (Arg *A = Args.getLastArg(OPT_fthinlto_index_EQ)) {
     if (IK.getLanguage() != Language::LLVM_IR)
       Diags.Report(diag::err_drv_argument_only_allowed_with)
           << A->getAsString(Args) << "-x ir";
     Opts.ThinLTOIndexFile =
         std::string(Args.getLastArgValue(OPT_fthinlto_index_EQ));
   }
   if (Arg *A = Args.getLastArg(OPT_save_temps_EQ))