Add -fno-jump-tables and-fjump-tables flags

Add no-jump-tables flag to disable use of jump tables when lowering
switch statements

Reviewers: echristo, hans

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D18407

llvm-svn: 265425

clang/include/clang/Driver/Options.td

@@ -586,6 +586,9 @@ def fno_math_errno : Flag<["-"], "fno-math-errno">, Group<f_Group>;
 def fbracket_depth_EQ : Joined<["-"], "fbracket-depth=">, Group<f_Group>;
 def fsignaling_math : Flag<["-"], "fsignaling-math">, Group<f_Group>;
 def fno_signaling_math : Flag<["-"], "fno-signaling-math">, Group<f_Group>;
+def fjump_tables : Flag<["-"], "fjump-tables">, Group<f_Group>;
+def fno_jump_tables : Flag<["-"], "fno-jump-tables">, Group<f_Group>, Flags<[CC1Option]>,
+  HelpText<"Do not use jump tables for lowering switches">;
 def fsanitize_EQ : CommaJoined<["-"], "fsanitize=">, Group<f_clang_Group>,
                    Flags<[CC1Option, CoreOption]>, MetaVarName<"<check>">,
                    HelpText<"Turn on runtime checks for various forms of undefined "

clang/include/clang/Frontend/CodeGenOptions.def

@@ -149,6 +149,7 @@ CODEGENOPT(UnitAtATime       , 1, 1) ///< Unused. For mirroring GCC optimization
                                      ///< selection.
 CODEGENOPT(UnrollLoops       , 1, 0) ///< Control whether loops are unrolled.
 CODEGENOPT(RerollLoops       , 1, 0) ///< Control whether loops are rerolled.
+CODEGENOPT(NoUseJumpTables   , 1, 0) ///< Set when -fno-jump-tables is enabled
 CODEGENOPT(UnsafeFPMath      , 1, 0) ///< Allow unsafe floating point optzns.
 CODEGENOPT(UnwindTables      , 1, 0) ///< Emit unwind tables.
 CODEGENOPT(VectorizeBB       , 1, 0) ///< Run basic block vectorizer.

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -711,6 +711,10 @@ void CodeGenFunction::StartFunction(GlobalDecl GD,
       Fn->addFnAttr(llvm::Attribute::NoInline);
   }
 
+  // Add no-jump-tables value.
+  Fn->addFnAttr("no-jump-tables",
+                llvm::toStringRef(CGM.getCodeGenOpts().NoUseJumpTables));
+
   if (getLangOpts().OpenCL) {
     // Add metadata for a kernel function.
     if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D))

clang/lib/Driver/Tools.cpp

@@ -3891,6 +3891,10 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     A->claim();
   }
 
+  if (!Args.hasFlag(options::OPT_fjump_tables, options::OPT_fno_jump_tables,
+                    true))
+    CmdArgs.push_back("-fno-jump-tables");
+
   if (Arg *A = Args.getLastArg(options::OPT_mregparm_EQ)) {
     CmdArgs.push_back("-mregparm");
     CmdArgs.push_back(A->getValue());

clang/lib/Frontend/CompilerInvocation.cpp

@@ -606,6 +606,8 @@ static bool ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args, InputKind IK,
 
   Opts.MergeFunctions = Args.hasArg(OPT_fmerge_functions);
 
+  Opts.NoUseJumpTables = Args.hasArg(OPT_fno_jump_tables);
+
   Opts.PrepareForLTO = Args.hasArg(OPT_flto, OPT_flto_EQ);
   const Arg *A = Args.getLastArg(OPT_flto, OPT_flto_EQ);
   Opts.EmitSummaryIndex = A && A->containsValue("thin");

clang/test/CodeGen/nousejumptable.c

@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -S -fno-jump-tables %s -emit-llvm -o - | FileCheck %s
+
+// CHECK-LABEL: main
+// CHECK: attributes #0 = {{.*}}"no-jump-tables"="true"{{.*}}
+
+int main() {
+  return 0;
+}