[Clang][Driver] Add an option to control loop-interchange (#125830)

This introduces options `-floop-interchange` and `-fno-loop-interchange`
to enable/disable the loop-interchange pass. This is part of the work
that tries to get that pass enabled by default (#124911), where it was
remarked that a user facing option to control this would be convenient
to have. The option name is the same as GCC's.

Author: sjoerdmeijer

clang/include/clang/Basic/CodeGenOptions.def

@@ -320,6 +320,7 @@ CODEGENOPT(TimePassesPerRun  , 1, 0) ///< Set when -ftime-report=per-pass-run is
 CODEGENOPT(TimeTrace         , 1, 0) ///< Set when -ftime-trace is enabled.
 VALUE_CODEGENOPT(TimeTraceGranularity, 32, 500) ///< Minimum time granularity (in microseconds),
                                                ///< traced by time profiler
+CODEGENOPT(InterchangeLoops  , 1, 0) ///< Run loop-interchange.
 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.

clang/include/clang/Driver/Options.td

@@ -4069,6 +4069,10 @@ def ftrap_function_EQ : Joined<["-"], "ftrap-function=">, Group<f_Group>,
   Visibility<[ClangOption, CC1Option]>,
   HelpText<"Issue call to specified function rather than a trap instruction">,
   MarshallingInfoString<CodeGenOpts<"TrapFuncName">>;
+def floop_interchange : Flag<["-"], "floop-interchange">, Group<f_Group>,
+  HelpText<"Enable the loop interchange pass">, Visibility<[ClangOption, CC1Option]>;
+def fno_loop_interchange: Flag<["-"], "fno-loop-interchange">, Group<f_Group>,
+  HelpText<"Disable the loop interchange pass">, Visibility<[ClangOption, CC1Option]>;
 def funroll_loops : Flag<["-"], "funroll-loops">, Group<f_Group>,
   HelpText<"Turn on loop unroller">, Visibility<[ClangOption, CC1Option, FlangOption, FC1Option]>;
 def fno_unroll_loops : Flag<["-"], "fno-unroll-loops">, Group<f_Group>,

clang/lib/CodeGen/BackendUtil.cpp

@@ -890,6 +890,7 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
 
   PipelineTuningOptions PTO;
   PTO.LoopUnrolling = CodeGenOpts.UnrollLoops;
+  PTO.LoopInterchange = CodeGenOpts.InterchangeLoops;
   // For historical reasons, loop interleaving is set to mirror setting for loop
   // unrolling.
   PTO.LoopInterleaving = CodeGenOpts.UnrollLoops;
@@ -1314,6 +1315,7 @@ runThinLTOBackend(CompilerInstance &CI, ModuleSummaryIndex *CombinedIndex,
   initTargetOptions(CI, Diags, Conf.Options);
   Conf.SampleProfile = std::move(SampleProfile);
   Conf.PTO.LoopUnrolling = CGOpts.UnrollLoops;
+  Conf.PTO.LoopInterchange = CGOpts.InterchangeLoops;
   // For historical reasons, loop interleaving is set to mirror setting for loop
   // unrolling.
   Conf.PTO.LoopInterleaving = CGOpts.UnrollLoops;

clang/lib/Driver/ToolChains/Clang.cpp

@@ -6974,6 +6974,8 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   Args.AddLastArg(CmdArgs, options::OPT_fwritable_strings);
   Args.AddLastArg(CmdArgs, options::OPT_funroll_loops,
                   options::OPT_fno_unroll_loops);
+  Args.AddLastArg(CmdArgs, options::OPT_floop_interchange,
+                  options::OPT_fno_loop_interchange);
 
   Args.AddLastArg(CmdArgs, options::OPT_fstrict_flex_arrays_EQ);
 

clang/lib/Frontend/CompilerInvocation.cpp

@@ -1665,6 +1665,11 @@ void CompilerInvocationBase::GenerateCodeGenArgs(const CodeGenOptions &Opts,
   else if (!Opts.UnrollLoops && Opts.OptimizationLevel > 1)
     GenerateArg(Consumer, OPT_fno_unroll_loops);
 
+  if (Opts.InterchangeLoops)
+    GenerateArg(Consumer, OPT_floop_interchange);
+  else
+    GenerateArg(Consumer, OPT_fno_loop_interchange);
+
   if (!Opts.BinutilsVersion.empty())
     GenerateArg(Consumer, OPT_fbinutils_version_EQ, Opts.BinutilsVersion);
 
@@ -1971,6 +1976,8 @@ bool CompilerInvocation::ParseCodeGenArgs(CodeGenOptions &Opts, ArgList &Args,
   Opts.UnrollLoops =
       Args.hasFlag(OPT_funroll_loops, OPT_fno_unroll_loops,
                    (Opts.OptimizationLevel > 1));
+  Opts.InterchangeLoops =
+      Args.hasFlag(OPT_floop_interchange, OPT_fno_loop_interchange, false);
   Opts.BinutilsVersion =
       std::string(Args.getLastArgValue(OPT_fbinutils_version_EQ));
 

clang/test/Driver/clang_f_opts.c

@@ -45,6 +45,13 @@
 // CHECK-UNROLL-LOOPS: "-funroll-loops"
 // CHECK-NO-UNROLL-LOOPS: "-fno-unroll-loops"
 
+// RUN: %clang -### -S -floop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-INTERCHANGE-LOOPS %s
+// RUN: %clang -### -S -fno-loop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-NO-INTERCHANGE-LOOPS %s
+// RUN: %clang -### -S -fno-loop-interchange -floop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-INTERCHANGE-LOOPS %s
+// RUN: %clang -### -S -floop-interchange -fno-loop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-NO-INTERCHANGE-LOOPS %s
+// CHECK-INTERCHANGE-LOOPS: "-floop-interchange"
+// CHECK-NO-INTERCHANGE-LOOPS: "-fno-loop-interchange"
+
 // RUN: %clang -### -S -fprofile-sample-accurate %s 2>&1 | FileCheck -check-prefix=CHECK-PROFILE-SAMPLE-ACCURATE %s
 // CHECK-PROFILE-SAMPLE-ACCURATE: "-fprofile-sample-accurate"
 

llvm/include/llvm/Passes/PassBuilder.h

@@ -60,6 +60,10 @@ class PipelineTuningOptions {
   /// Tuning option to enable/disable loop unrolling. Its default value is true.
   bool LoopUnrolling;
 
+  /// Tuning option to enable/disable loop interchange. Its default value is
+  /// false.
+  bool LoopInterchange;
+
   /// Tuning option to forget all SCEV loops in LoopUnroll. Its default value
   /// is that of the flag: `-forget-scev-loop-unroll`.
   bool ForgetAllSCEVInLoopUnroll;

llvm/lib/Passes/PassBuilderPipelines.cpp

@@ -200,9 +200,9 @@ static cl::opt<bool> ExtraVectorizerPasses(
 static cl::opt<bool> RunNewGVN("enable-newgvn", cl::init(false), cl::Hidden,
                                cl::desc("Run the NewGVN pass"));
 
-static cl::opt<bool> EnableLoopInterchange(
-    "enable-loopinterchange", cl::init(false), cl::Hidden,
-    cl::desc("Enable the experimental LoopInterchange Pass"));
+static cl::opt<bool>
+    EnableLoopInterchange("enable-loopinterchange", cl::init(false), cl::Hidden,
+                          cl::desc("Enable the LoopInterchange Pass"));
 
 static cl::opt<bool> EnableUnrollAndJam("enable-unroll-and-jam",
                                         cl::init(false), cl::Hidden,
@@ -316,6 +316,7 @@ PipelineTuningOptions::PipelineTuningOptions() {
   LoopVectorization = true;
   SLPVectorization = false;
   LoopUnrolling = true;
+  LoopInterchange = EnableLoopInterchange;
   ForgetAllSCEVInLoopUnroll = ForgetSCEVInLoopUnroll;
   LicmMssaOptCap = SetLicmMssaOptCap;
   LicmMssaNoAccForPromotionCap = SetLicmMssaNoAccForPromotionCap;
@@ -485,7 +486,7 @@ PassBuilder::buildO1FunctionSimplificationPipeline(OptimizationLevel Level,
 
   LPM2.addPass(LoopDeletionPass());
 
-  if (EnableLoopInterchange)
+  if (PTO.LoopInterchange)
     LPM2.addPass(LoopInterchangePass());
 
   // Do not enable unrolling in PreLinkThinLTO phase during sample PGO
@@ -676,7 +677,7 @@ PassBuilder::buildFunctionSimplificationPipeline(OptimizationLevel Level,
 
   LPM2.addPass(LoopDeletionPass());
 
-  if (EnableLoopInterchange)
+  if (PTO.LoopInterchange)
     LPM2.addPass(LoopInterchangePass());
 
   // Do not enable unrolling in PreLinkThinLTO phase during sample PGO