Frontend: Add an Osize optimization option

This adds an size optimization mode ("Osize") which intends to enable some
optimization but targets mainly reduced code size compared to the regular
optimized mode ("O").

rdar://33075751

Author: aschwaighofer

include/swift/AST/IRGenOptions.h

@@ -96,6 +96,9 @@ class IRGenOptions {
   /// Whether or not to run optimization passes.
   unsigned Optimize : 1;
 
+  /// Whether or not to optimize for code size.
+  unsigned OptimizeForSize : 1;
+
   /// Which sanitizer is turned on.
   SanitizerKind Sanitize : 2;
 
@@ -172,7 +175,8 @@ class IRGenOptions {
 
   IRGenOptions()
       : DWARFVersion(2), OutputKind(IRGenOutputKind::LLVMAssembly),
-        Verify(true), Optimize(false), Sanitize(SanitizerKind::None),
+        Verify(true), Optimize(false), OptimizeForSize(false),
+        Sanitize(SanitizerKind::None),
         DebugInfoKind(IRGenDebugInfoKind::None), UseJIT(false),
         DisableLLVMOptzns(false), DisableLLVMARCOpts(false),
         DisableLLVMSLPVectorizer(false), DisableFPElim(true), Playground(false),
@@ -196,6 +200,7 @@ class IRGenOptions {
   unsigned getLLVMCodeGenOptionsHash() {
     unsigned Hash = 0;
     Hash = (Hash << 1) | Optimize;
+    Hash = (Hash << 1) | OptimizeForSize;
     Hash = (Hash << 1) | DisableLLVMOptzns;
     Hash = (Hash << 1) | DisableLLVMARCOpts;
     return Hash;

include/swift/AST/SILOptions.h

@@ -51,6 +51,7 @@ class SILOptions {
     None,
     Debug,
     Optimize,
+    OptimizeForSize,
     OptimizeUnchecked
   };
 

include/swift/Option/Options.td

@@ -374,6 +374,8 @@ def Onone : Flag<["-"], "Onone">, Group<O_Group>, Flags<[FrontendOption]>,
   HelpText<"Compile without any optimization">;
 def O : Flag<["-"], "O">, Group<O_Group>, Flags<[FrontendOption]>,
   HelpText<"Compile with optimizations">;
+def Osize : Flag<["-"], "Osize">, Group<O_Group>, Flags<[FrontendOption]>,
+  HelpText<"Compile with optimizations and target small code size">;
 def Ounchecked : Flag<["-"], "Ounchecked">, Group<O_Group>,
   Flags<[FrontendOption]>,
   HelpText<"Compile with optimizations and remove runtime safety checks">;

lib/Frontend/CompilerInvocation.cpp

@@ -1373,23 +1373,34 @@ static bool ParseSILArgs(SILOptions &Opts, ArgList &Args,
     Args.hasArg(OPT_sil_serialize_witness_tables);
 
   // Parse the optimization level.
+  // Default to Onone settings if no option is passed.
+  IRGenOpts.Optimize = false;
+  IRGenOpts.OptimizeForSize = false;
+  Opts.Optimization = SILOptions::SILOptMode::None;
   if (const Arg *A = Args.getLastArg(OPT_O_Group)) {
     if (A->getOption().matches(OPT_Onone)) {
       IRGenOpts.Optimize = false;
       Opts.Optimization = SILOptions::SILOptMode::None;
     } else if (A->getOption().matches(OPT_Ounchecked)) {
       // Turn on optimizations and remove all runtime checks.
       IRGenOpts.Optimize = true;
+      IRGenOpts.OptimizeForSize = false;
       Opts.Optimization = SILOptions::SILOptMode::OptimizeUnchecked;
       // Removal of cond_fail (overflow on binary operations).
       Opts.RemoveRuntimeAsserts = true;
       Opts.AssertConfig = SILOptions::Unchecked;
     } else if (A->getOption().matches(OPT_Oplayground)) {
       // For now -Oplayground is equivalent to -Onone.
       IRGenOpts.Optimize = false;
+      IRGenOpts.OptimizeForSize = false;
       Opts.Optimization = SILOptions::SILOptMode::None;
+    } else if (A->getOption().matches(OPT_Osize)) {
+      IRGenOpts.Optimize = true;
+      IRGenOpts.OptimizeForSize = true;
+      Opts.Optimization = SILOptions::SILOptMode::OptimizeForSize;
     } else {
       assert(A->getOption().matches(OPT_O));
+      IRGenOpts.OptimizeForSize = false;
       IRGenOpts.Optimize = true;
       Opts.Optimization = SILOptions::SILOptMode::Optimize;
     }

lib/FrontendTool/FrontendTool.cpp

@@ -1024,6 +1024,7 @@ static bool emitIndexData(SourceFile *PrimarySourceFile,
       isDebugCompilation = true;
       break;
     case SILOptions::SILOptMode::Optimize:
+    case SILOptions::SILOptMode::OptimizeForSize:
     case SILOptions::SILOptMode::OptimizeUnchecked:
       isDebugCompilation = false;
       break;
@@ -1123,6 +1124,8 @@ silOptModeArgStr(SILOptions::SILOptMode mode) {
    return "O";
  case SILOptions::SILOptMode::OptimizeUnchecked:
    return "Ounchecked";
+ case SILOptions::SILOptMode::OptimizeForSize:
+   return "Osize";
  default:
    return "Onone";
   }