[clang] Add -ffinite-loops & -fno-finite-loops options.

This cherry-picks the following patches on the release branch:

6280bb4 [clang] Remove redundant condition (NFC).
51bf4c0 [clang] Add -ffinite-loops & -fno-finite-loops options.
fb4d8fe [clang] Update mustprogress tests

This patch adds 2 new options to control when Clang adds `mustprogress`:

  1. -ffinite-loops: assume all loops are finite; mustprogress is added
     to all loops, regardless of the selected language standard.
  2. -fno-finite-loops: assume no loop is finite; mustprogress is not
     added to any loop or function. We could add mustprogress to
     functions without loops, but we would have to detect that in Clang,
     which is probably not worth it.

Differential Revision: https://reviews.llvm.org/D96850

Author: fhahn

clang/include/clang/Basic/CodeGenOptions.def

@@ -266,6 +266,9 @@ CODEGENOPT(VectorizeLoop     , 1, 0) ///< Run loop vectorizer.
 CODEGENOPT(VectorizeSLP      , 1, 0) ///< Run SLP vectorizer.
 CODEGENOPT(ProfileSampleAccurate, 1, 0) ///< Sample profile is accurate.
 
+/// Treat loops as finite: language, always, never.
+ENUM_CODEGENOPT(FiniteLoops, FiniteLoopsKind, 2, FiniteLoopsKind::Language)
+
   /// Attempt to use register sized accesses to bit-fields in structures, when
   /// possible.
 CODEGENOPT(UseRegisterSizedBitfieldAccess , 1, 0)

clang/include/clang/Basic/CodeGenOptions.h

@@ -140,6 +140,12 @@ class CodeGenOptions : public CodeGenOptionsBase {
     All,         // Keep all frame pointers.
   };
 
+  enum FiniteLoopsKind {
+    Language, // Not specified, use language standard.
+    Always,   // All loops are assumed to be finite.
+    Never,    // No loop is assumed to be finite.
+  };
+
   /// The code model to use (-mcmodel).
   std::string CodeModel;
 

clang/include/clang/Driver/Options.td

@@ -2410,6 +2410,11 @@ def fno_unroll_loops : Flag<["-"], "fno-unroll-loops">, Group<f_Group>,
 defm reroll_loops : BoolFOption<"reroll-loops",
   CodeGenOpts<"RerollLoops">, DefaultFalse,
   PosFlag<SetTrue, [CC1Option], "Turn on loop reroller">, NegFlag<SetFalse>>;
+def ffinite_loops: Flag<["-"],  "ffinite-loops">, Group<f_Group>,
+  HelpText<"Assume all loops are finite.">, Flags<[CC1Option]>;
+def fno_finite_loops: Flag<["-"], "fno-finite-loops">, Group<f_Group>,
+  HelpText<"Do not assume that any loop is finite.">, Flags<[CC1Option]>;
+
 def ftrigraphs : Flag<["-"], "ftrigraphs">, Group<f_Group>,
   HelpText<"Process trigraph sequences">, Flags<[CC1Option]>;
 def fno_trigraphs : Flag<["-"], "fno-trigraphs">, Group<f_Group>,

clang/lib/CodeGen/CodeGenFunction.h

@@ -507,12 +507,23 @@ class CodeGenFunction : public CodeGenTypeCache {
 
   /// True if the C++ Standard Requires Progress.
   bool CPlusPlusWithProgress() {
+    if (CGM.getCodeGenOpts().getFiniteLoops() ==
+        CodeGenOptions::FiniteLoopsKind::Never)
+      return false;
+
     return getLangOpts().CPlusPlus11 || getLangOpts().CPlusPlus14 ||
            getLangOpts().CPlusPlus17 || getLangOpts().CPlusPlus20;
   }
 
   /// True if the C Standard Requires Progress.
   bool CWithProgress() {
+    if (CGM.getCodeGenOpts().getFiniteLoops() ==
+        CodeGenOptions::FiniteLoopsKind::Always)
+      return true;
+    if (CGM.getCodeGenOpts().getFiniteLoops() ==
+        CodeGenOptions::FiniteLoopsKind::Never)
+      return false;
+
     return getLangOpts().C11 || getLangOpts().C17 || getLangOpts().C2x;
   }
 

clang/lib/Driver/ToolChains/Clang.cpp

@@ -5620,6 +5620,9 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
     if (A->getOption().matches(options::OPT_freroll_loops))
       CmdArgs.push_back("-freroll-loops");
 
+  Args.AddLastArg(CmdArgs, options::OPT_ffinite_loops,
+                  options::OPT_fno_finite_loops);
+
   Args.AddLastArg(CmdArgs, options::OPT_fwritable_strings);
   Args.AddLastArg(CmdArgs, options::OPT_funroll_loops,
                   options::OPT_fno_unroll_loops);

clang/lib/Frontend/CompilerInvocation.cpp

@@ -1037,7 +1037,6 @@ bool CompilerInvocation::ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args,
   Opts.UnrollLoops =
       Args.hasFlag(OPT_funroll_loops, OPT_fno_unroll_loops,
                    (Opts.OptimizationLevel > 1));
-
   Opts.BinutilsVersion =
       std::string(Args.getLastArgValue(OPT_fbinutils_version_EQ));
 
@@ -1324,6 +1323,10 @@ bool CompilerInvocation::ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args,
 
   Opts.EmitVersionIdentMetadata = Args.hasFlag(OPT_Qy, OPT_Qn, true);
 
+  if (Args.hasArg(options::OPT_ffinite_loops))
+    Opts.FiniteLoops = CodeGenOptions::FiniteLoopsKind::Always;
+  else if (Args.hasArg(options::OPT_fno_finite_loops))
+    Opts.FiniteLoops = CodeGenOptions::FiniteLoopsKind::Never;
   return Success;
 }