[flang] add -floop-interchange and enable it with opt levels (#140182)

Enable the use of -floop-interchange from the flang driver.
Enable in flang LLVM's loop interchange at levels -O2, -O3, -Ofast, and -Os.

Author: sebpop

clang/include/clang/Driver/Options.td

@@ -4186,9 +4186,9 @@ def ftrap_function_EQ : Joined<["-"], "ftrap-function=">, Group<f_Group>,
   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]>;
+  HelpText<"Enable the loop interchange pass">, Visibility<[ClangOption, CC1Option, FlangOption, FC1Option]>;
 def fno_loop_interchange: Flag<["-"], "fno-loop-interchange">, Group<f_Group>,
-  HelpText<"Disable the loop interchange pass">, Visibility<[ClangOption, CC1Option]>;
+  HelpText<"Disable the loop interchange pass">, Visibility<[ClangOption, CC1Option, FlangOption, FC1Option]>;
 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/Driver/ToolChains/CommonArgs.cpp

@@ -3150,3 +3150,16 @@ void tools::handleVectorizeSLPArgs(const ArgList &Args,
                    options::OPT_fno_slp_vectorize, EnableSLPVec))
     CmdArgs.push_back("-vectorize-slp");
 }
+
+void tools::handleInterchangeLoopsArgs(const ArgList &Args,
+                                       ArgStringList &CmdArgs) {
+  // FIXME: instead of relying on shouldEnableVectorizerAtOLevel, we may want to
+  // implement a separate function to infer loop interchange from opt level.
+  // For now, enable loop-interchange at the same opt levels as loop-vectorize.
+  bool EnableInterchange = shouldEnableVectorizerAtOLevel(Args, false);
+  OptSpecifier InterchangeAliasOption =
+      EnableInterchange ? options::OPT_O_Group : options::OPT_floop_interchange;
+  if (Args.hasFlag(options::OPT_floop_interchange, InterchangeAliasOption,
+                   options::OPT_fno_loop_interchange, EnableInterchange))
+    CmdArgs.push_back("-floop-interchange");
+}

clang/lib/Driver/ToolChains/CommonArgs.h

@@ -259,6 +259,10 @@ void renderCommonIntegerOverflowOptions(const llvm::opt::ArgList &Args,
 bool shouldEnableVectorizerAtOLevel(const llvm::opt::ArgList &Args,
                                     bool isSlpVec);
 
+/// Enable -floop-interchange based on the optimization level selected.
+void handleInterchangeLoopsArgs(const llvm::opt::ArgList &Args,
+                                llvm::opt::ArgStringList &CmdArgs);
+
 /// Enable -fvectorize based on the optimization level selected.
 void handleVectorizeLoopsArgs(const llvm::opt::ArgList &Args,
                               llvm::opt::ArgStringList &CmdArgs);

clang/lib/Driver/ToolChains/Flang.cpp

@@ -152,6 +152,7 @@ void Flang::addCodegenOptions(const ArgList &Args,
       !stackArrays->getOption().matches(options::OPT_fno_stack_arrays))
     CmdArgs.push_back("-fstack-arrays");
 
+  handleInterchangeLoopsArgs(Args, CmdArgs);
   handleVectorizeLoopsArgs(Args, CmdArgs);
   handleVectorizeSLPArgs(Args, CmdArgs);
 

flang/docs/ReleaseNotes.md

@@ -32,6 +32,9 @@ page](https://llvm.org/releases/).
 
 ## New Compiler Flags
 
+* -floop-interchange is now recognized by flang.
+* -floop-interchange is enabled by default at -O2 and above.
+
 ## Windows Support
 
 ## Fortran Language Changes in Flang

flang/include/flang/Frontend/CodeGenOptions.def

@@ -35,6 +35,7 @@ CODEGENOPT(PrepareForThinLTO , 1, 0) ///< Set when -flto=thin is enabled on the
 CODEGENOPT(StackArrays, 1, 0) ///< -fstack-arrays (enable the stack-arrays pass)
 CODEGENOPT(VectorizeLoop, 1, 0) ///< Enable loop vectorization.
 CODEGENOPT(VectorizeSLP, 1, 0) ///< Enable SLP vectorization.
+CODEGENOPT(InterchangeLoops, 1, 0) ///< Enable loop interchange.
 CODEGENOPT(LoopVersioning, 1, 0) ///< Enable loop versioning.
 CODEGENOPT(UnrollLoops, 1, 0) ///< Enable loop unrolling
 CODEGENOPT(AliasAnalysis, 1, 0) ///< Enable alias analysis pass

flang/lib/Frontend/CompilerInvocation.cpp

@@ -270,6 +270,9 @@ static void parseCodeGenArgs(Fortran::frontend::CodeGenOptions &opts,
                    clang::driver::options::OPT_fno_stack_arrays, false))
     opts.StackArrays = 1;
 
+  if (args.getLastArg(clang::driver::options::OPT_floop_interchange))
+    opts.InterchangeLoops = 1;
+
   if (args.getLastArg(clang::driver::options::OPT_vectorize_loops))
     opts.VectorizeLoop = 1;
 

flang/lib/Frontend/FrontendActions.cpp

@@ -922,6 +922,7 @@ void CodeGenAction::runOptimizationPipeline(llvm::raw_pwrite_stream &os) {
   if (ci.isTimingEnabled())
     si.getTimePasses().setOutStream(ci.getTimingStreamLLVM());
   pto.LoopUnrolling = opts.UnrollLoops;
+  pto.LoopInterchange = opts.InterchangeLoops;
   pto.LoopInterleaving = opts.UnrollLoops;
   pto.LoopVectorization = opts.VectorizeLoop;
   pto.SLPVectorization = opts.VectorizeSLP;

flang/test/Driver/loop-interchange.f90

@@ -0,0 +1,17 @@
+! RUN: %flang -### -S -floop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-LOOP-INTERCHANGE %s
+! RUN: %flang -### -S -fno-loop-interchange %s 2>&1 | FileCheck -check-prefix=CHECK-NO-LOOP-INTERCHANGE %s
+! RUN: %flang -### -S -O0 %s 2>&1 | FileCheck -check-prefix=CHECK-NO-LOOP-INTERCHANGE %s
+! RUN: %flang -### -S -O1 %s 2>&1 | FileCheck -check-prefix=CHECK-NO-LOOP-INTERCHANGE %s
+! RUN: %flang -### -S -O2 %s 2>&1 | FileCheck -check-prefix=CHECK-LOOP-INTERCHANGE %s
+! RUN: %flang -### -S -O3 %s 2>&1 | FileCheck -check-prefix=CHECK-LOOP-INTERCHANGE %s
+! RUN: %flang -### -S -Os %s 2>&1 | FileCheck -check-prefix=CHECK-LOOP-INTERCHANGE %s
+! RUN: %flang -### -S -Oz %s 2>&1 | FileCheck -check-prefix=CHECK-NO-LOOP-INTERCHANGE %s
+! CHECK-LOOP-INTERCHANGE: "-floop-interchange"
+! CHECK-NO-LOOP-INTERCHANGE-NOT: "-floop-interchange"
+! RUN: %flang_fc1 -emit-llvm -O2 -floop-interchange -mllvm -print-pipeline-passes -o /dev/null %s 2>&1 | FileCheck -check-prefix=CHECK-LOOP-INTERCHANGE-PASS %s
+! RUN: %flang_fc1 -emit-llvm -O2 -fno-loop-interchange -mllvm -print-pipeline-passes -o /dev/null %s 2>&1 | FileCheck -check-prefix=CHECK-NO-LOOP-INTERCHANGE-PASS %s
+! CHECK-LOOP-INTERCHANGE-PASS: loop-interchange
+! CHECK-NO-LOOP-INTERCHANGE-PASS-NOT: loop-interchange
+
+program test
+end program