[clang-cl] Map /Ot to -O3 instead of -O2 (#95406)

/Ot (which is also implied by /O2) is supposed to optimize for maximum
speed, so -O3 seems like a better match.

Author: zmodem

clang/docs/ReleaseNotes.rst

@@ -921,6 +921,10 @@ Android Support
 Windows Support
 ^^^^^^^^^^^^^^^
 
+- The clang-cl ``/Ot`` compiler option ("optimize for speed", also implied by
+  ``/O2``) now maps to clang's ``-O3`` optimizataztion level instead of ``-O2``.
+  Users who prefer the old behavior can use ``clang-cl /Ot /clang:-O2 ...``.
+
 - Clang-cl now supports function targets with intrinsic headers. This allows
   for runtime feature detection of intrinsics. Previously under clang-cl
   ``immintrin.h`` and similar intrinsic headers would only include the intrinsics

clang/docs/UsersManual.rst

@@ -4636,8 +4636,8 @@ Execute ``clang-cl /?`` to see a list of supported options:
       /Og                     No effect
       /Oi-                    Disable use of builtin functions
       /Oi                     Enable use of builtin functions
-      /Os                     Optimize for size
-      /Ot                     Optimize for speed
+      /Os                     Optimize for size (like clang -Os)
+      /Ot                     Optimize for speed (like clang -O3)
       /Ox                     Deprecated (same as /Og /Oi /Ot /Oy /Ob2); use /O2 instead
       /Oy-                    Disable frame pointer omission (x86 only, default)
       /Oy                     Enable frame pointer omission (x86 only)

clang/include/clang/Driver/Options.td

@@ -8279,9 +8279,9 @@ def : CLFlag<"Oi">, Alias<_SLASH_O>, AliasArgs<["i"]>,
 def : CLFlag<"Oi-">, Alias<_SLASH_O>, AliasArgs<["i-"]>,
   HelpText<"Disable use of builtin functions">;
 def : CLFlag<"Os">, Alias<_SLASH_O>, AliasArgs<["s"]>,
-  HelpText<"Optimize for size">;
+  HelpText<"Optimize for size (like clang -Os)">;
 def : CLFlag<"Ot">, Alias<_SLASH_O>, AliasArgs<["t"]>,
-  HelpText<"Optimize for speed">;
+  HelpText<"Optimize for speed (like clang -O3)">;
 def : CLFlag<"Ox">, Alias<_SLASH_O>, AliasArgs<["x"]>,
   HelpText<"Deprecated (like /Og /Oi /Ot /Oy /Ob2); use /O2">;
 def : CLFlag<"Oy">, Alias<_SLASH_O>, AliasArgs<["y"]>,

clang/lib/Driver/ToolChains/MSVC.cpp

@@ -861,7 +861,7 @@ static void TranslateOptArg(Arg *A, llvm::opt::DerivedArgList &DAL,
           DAL.AddJoinedArg(A, Opts.getOption(options::OPT_O), "s");
         } else if (OptChar == '2' || OptChar == 'x') {
           DAL.AddFlagArg(A, Opts.getOption(options::OPT_fbuiltin));
-          DAL.AddJoinedArg(A, Opts.getOption(options::OPT_O), "2");
+          DAL.AddJoinedArg(A, Opts.getOption(options::OPT_O), "3");
         }
         if (SupportsForcingFramePointer &&
             !DAL.hasArgNoClaim(options::OPT_fno_omit_frame_pointer))
@@ -901,7 +901,7 @@ static void TranslateOptArg(Arg *A, llvm::opt::DerivedArgList &DAL,
       DAL.AddJoinedArg(A, Opts.getOption(options::OPT_O), "s");
       break;
     case 't':
-      DAL.AddJoinedArg(A, Opts.getOption(options::OPT_O), "2");
+      DAL.AddJoinedArg(A, Opts.getOption(options::OPT_O), "3");
       break;
     case 'y': {
       bool OmitFramePointer = true;

clang/test/Driver/cl-options.c

@@ -189,27 +189,27 @@
 // RUN: %clang_cl /Ot --target=i686-pc-windows-msvc -### -- %s 2>&1 | FileCheck -check-prefix=Ot %s
 // RUN: %clang_cl /Ot --target=x86_64-pc-windows-msvc -### -- %s 2>&1 | FileCheck -check-prefix=Ot %s
 // Ot: -mframe-pointer=none
-// Ot: -O2
+// Ot: -O3
 
 // RUN: %clang_cl /Ox --target=i686-pc-windows-msvc -### -- %s 2>&1 | FileCheck -check-prefix=Ox %s
 // RUN: %clang_cl /Ox --target=x86_64-pc-windows-msvc -### -- %s 2>&1 | FileCheck -check-prefix=Ox %s
 // Ox: -mframe-pointer=none
-// Ox: -O2
+// Ox: -O3
 
 // RUN: %clang_cl --target=i686-pc-win32 /O2sy- -### -- %s 2>&1 | FileCheck -check-prefix=PR24003 %s
 // PR24003: -mframe-pointer=all
 // PR24003: -Os
 
 // RUN: %clang_cl --target=i686-pc-win32 -Werror -Wno-msvc-not-found /Oy- /O2 -### -- %s 2>&1 | FileCheck -check-prefix=Oy_2 %s
 // Oy_2: -mframe-pointer=all
-// Oy_2: -O2
+// Oy_2: -O3
 
 // RUN: %clang_cl --target=aarch64-pc-windows-msvc -Werror -Wno-msvc-not-found /Oy- /O2 -### -- %s 2>&1 | FileCheck -check-prefix=Oy_aarch64 %s
 // Oy_aarch64: -mframe-pointer=non-leaf
-// Oy_aarch64: -O2
+// Oy_aarch64: -O3
 
 // RUN: %clang_cl --target=i686-pc-win32 -Werror -Wno-msvc-not-found /O2 /O2 -### -- %s 2>&1 | FileCheck -check-prefix=O2O2 %s
-// O2O2: "-O2"
+// O2O2: "-O3"
 
 // RUN: %clang_cl /Zs -Werror /Oy -- %s 2>&1