[Driver] Default to -mcpu=ultrasparc3 on Solaris/SPARC (#149990)

Prompted by PR #149652, this patch changes the Solaris/SPARC default to
-mcpu, matching both the Oracle Studio 12.6 compilers and GCC 16:
[[PATCH] Default to -mcpu=ultrasparc3 on
Solaris/SPARC](https://gcc.gnu.org/pipermail/gcc-patches/2025-July/690191.html).
This is equivalent to enabling the `vis2` feature.

Tested on `sparcv9-sun-solaris2.11` and `sparc64-unknown-linux-gnu`.

Author: rorth

clang/lib/Driver/ToolChains/Arch/Sparc.cpp

@@ -23,7 +23,9 @@ const char *sparc::getSparcAsmModeForCPU(StringRef Name,
   if (Triple.getArch() == llvm::Triple::sparcv9) {
     const char *DefV9CPU;
 
-    if (Triple.isOSLinux() || Triple.isOSFreeBSD() || Triple.isOSOpenBSD())
+    if (Triple.isOSSolaris())
+      DefV9CPU = "-Av9b";
+    else if (Triple.isOSLinux() || Triple.isOSFreeBSD() || Triple.isOSOpenBSD())
       DefV9CPU = "-Av9a";
     else
       DefV9CPU = "-Av9";
@@ -157,6 +159,7 @@ void sparc::getSparcTargetFeatures(const Driver &D, const llvm::Triple &Triple,
   bool IsSparcV9ATarget =
       (Triple.getArch() == llvm::Triple::sparcv9) &&
       (Triple.isOSLinux() || Triple.isOSFreeBSD() || Triple.isOSOpenBSD());
+  bool IsSparcV9BTarget = Triple.isOSSolaris();
   if (Arg *A = Args.getLastArg(options::OPT_mvis, options::OPT_mno_vis)) {
     if (A->getOption().matches(options::OPT_mvis))
       Features.push_back("+vis");
@@ -171,6 +174,8 @@ void sparc::getSparcTargetFeatures(const Driver &D, const llvm::Triple &Triple,
       Features.push_back("+vis2");
     else
       Features.push_back("-vis2");
+  } else if (IsSparcV9BTarget) {
+    Features.push_back("+vis2");
   }
 
   if (Arg *A = Args.getLastArg(options::OPT_mvis3, options::OPT_mno_vis3)) {

clang/test/Driver/sparc-target-features.c

@@ -20,6 +20,11 @@
 
 // RUN: %clang --target=sparc -mvis2 %s -### 2>&1 | FileCheck -check-prefix=VIS2 %s
 // RUN: %clang --target=sparc -mno-vis2 %s -### 2>&1 | FileCheck -check-prefix=NO-VIS2 %s
+/// Solaris/SPARC defaults to -mvis2
+// RUN: %clang --target=sparc-sun-solaris2.11 %s -### 2>&1 | FileCheck -check-prefix=VIS2 %s
+// RUN: %clang --target=sparc-sun-solaris2.11 -mno-vis2 %s -### 2>&1 | FileCheck -check-prefix=NO-VIS2 %s
+// RUN: %clang --target=sparcv9-sun-solaris2.11 %s -### 2>&1 | FileCheck -check-prefix=VIS2 %s
+// RUN: %clang --target=sparcv9-sun-solaris2.11 -mno-vis2 %s -### 2>&1 | FileCheck -check-prefix=NO-VIS2 %s
 // VIS2: "-target-feature" "+vis2"
 // NO-VIS2: "-target-feature" "-vis2"