When optimizing for size, enable loop rerolling by default.

[hfinkel]

Summary

We have a loop-rerolling optimization which can be enabled by using -freroll-loops. While sometimes loops are hand-unrolled for performance reasons, when optimizing for size, we should always undo this manual optimization to produce smaller code (our optimizer's unroller will still unroll the rerolled loops if it thinks that is a good idea).

[jmolloy]

Good idea! LGTM!

[hfinkel]

r283685

lib/Driver/Tools.cpp

if (A->getOption().matches(options::OPT_fwrapv))
       CmdArgs.push_back("-fwrapv");
   } else if (Arg *A = Args.getLastArg(options::OPT_fstrict_overflow,
                                       options::OPT_fno_strict_overflow)) {
     if (A->getOption().matches(options::OPT_fno_strict_overflow))
       CmdArgs.push_back("-fwrapv");
   }
 
   if (Arg *A = Args.getLastArg(options::OPT_freroll_loops,
-                               options::OPT_fno_reroll_loops))
+                               options::OPT_fno_reroll_loops)) {
     if (A->getOption().matches(options::OPT_freroll_loops))
       CmdArgs.push_back("-freroll-loops");
+  } else if (Arg *A = Args.getLastArg(options::OPT_O_Group)) {
+    // If rerolling is not explicitly enabled or disabled, then enable when
+    // optimizing for size.
+    if (A->getOption().matches(options::OPT_O)) {
+      StringRef S(A->getValue());
+      if (S == "s" || S == "z")
+        CmdArgs.push_back("-freroll-loops");
+    }
+  }
 
   Args.AddLastArg(CmdArgs, options::OPT_fwritable_strings);
   Args.AddLastArg(CmdArgs, options::OPT_funroll_loops,
                   options::OPT_fno_unroll_loops);
 
   Args.AddLastArg(CmdArgs, options::OPT_pthread);
 
   // -stack-protector=0 is default.

test/Driver/clang_f_opts.c

 // RUN: %clang -### -S -funroll-loops %s 2>&1 | FileCheck -check-prefix=CHECK-UNROLL-LOOPS %s
 // RUN: %clang -### -S -fno-unroll-loops %s 2>&1 | FileCheck -check-prefix=CHECK-NO-UNROLL-LOOPS %s
 // RUN: %clang -### -S -fno-unroll-loops -funroll-loops %s 2>&1 | FileCheck -check-prefix=CHECK-UNROLL-LOOPS %s
 // RUN: %clang -### -S -funroll-loops -fno-unroll-loops %s 2>&1 | FileCheck -check-prefix=CHECK-NO-UNROLL-LOOPS %s
 // CHECK-UNROLL-LOOPS: "-funroll-loops"
 // CHECK-NO-UNROLL-LOOPS: "-fno-unroll-loops"
 
 // RUN: %clang -### -S -freroll-loops %s 2>&1 | FileCheck -check-prefix=CHECK-REROLL-LOOPS %s
+// RUN: %clang -### -S -Os %s 2>&1 | FileCheck -check-prefix=CHECK-REROLL-LOOPS %s
+// RUN: %clang -### -S -Oz %s 2>&1 | FileCheck -check-prefix=CHECK-REROLL-LOOPS %s
 // RUN: %clang -### -S -fno-reroll-loops %s 2>&1 | FileCheck -check-prefix=CHECK-NO-REROLL-LOOPS %s
+// RUN: %clang -### -S -Os -fno-reroll-loops %s 2>&1 | FileCheck -check-prefix=CHECK-NO-REROLL-LOOPS %s
+// RUN: %clang -### -S -Oz -fno-reroll-loops %s 2>&1 | FileCheck -check-prefix=CHECK-NO-REROLL-LOOPS %s
+// RUN: %clang -### -S -O1 %s 2>&1 | FileCheck -check-prefix=CHECK-NO-REROLL-LOOPS %s
 // RUN: %clang -### -S -fno-reroll-loops -freroll-loops %s 2>&1 | FileCheck -check-prefix=CHECK-REROLL-LOOPS %s
 // RUN: %clang -### -S -freroll-loops -fno-reroll-loops %s 2>&1 | FileCheck -check-prefix=CHECK-NO-REROLL-LOOPS %s
 // CHECK-REROLL-LOOPS: "-freroll-loops"
 // CHECK-NO-REROLL-LOOPS-NOT: "-freroll-loops"
 
 // RUN: %clang -### -S -fprofile-sample-use=%S/Inputs/file.prof %s 2>&1 | FileCheck -check-prefix=CHECK-SAMPLE-PROFILE %s
 // CHECK-SAMPLE-PROFILE: "-fprofile-sample-use={{.*}}/file.prof"