[flang] Disable loop interchange by default (#155279)

Disable loop interchange by default, while keeping the ability to
explicitly enable using `-floop-interchange`. This matches Clang.

See discussion on #140182.

(cherry picked from commit 8849750)

Author: nikic

clang/lib/Driver/ToolChains/CommonArgs.cpp

@@ -3265,14 +3265,8 @@ void tools::handleVectorizeSLPArgs(const ArgList &Args,
 
 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))
+  if (Args.hasFlag(options::OPT_floop_interchange,
+                   options::OPT_fno_loop_interchange, false))
     CmdArgs.push_back("-floop-interchange");
 }
 

flang/test/Driver/loop-interchange.f90

@@ -2,9 +2,9 @@
 ! 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 -O2 %s 2>&1 | FileCheck -check-prefix=CHECK-NO-LOOP-INTERCHANGE %s
+! RUN: %flang -### -S -O3 %s 2>&1 | FileCheck -check-prefix=CHECK-NO-LOOP-INTERCHANGE %s
+! RUN: %flang -### -S -Os %s 2>&1 | FileCheck -check-prefix=CHECK-NO-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"