[Driver] Fix linking with -lm on Solaris (#65632)

As noticed in D158846, the Solaris driver deviates from other targets in
that it links every executable with `-lm`, but doesn't for shared
objects. For C code, this is unnecessary, while for C++ `libm` is always
needed, even for shared objects.

This patch fixes this by following the `Gnu.cpp` precedent. It adjusts
the `solaris-ld.c` test accordingly, adding some more tests.

Tested on `amd64-pc-solaris2.11`, `sparcv9-sun-solaris2.11`, and
`x86_64-pc-linux-gnu`.

(cherry picked from commit 1e6b0df3503567488e7df2d574c90f8f31a001a2)

2 files changed, 22 insertions, 8 deletions

diff --git a/clang/lib/Driver/ToolChains/Solaris.cpp b/clang/lib/Driver/ToolChains/Solaris.cpp
index de5a69e4ca3f..85619a91554e 100644
--- a/clang/lib/Driver/ToolChains/Solaris.cpp
+++ b/clang/lib/Driver/ToolChains/Solaris.cpp
@@ -64,6 +64,7 @@ void solaris::Linker::ConstructJob(Compilation &C, const JobAction &JA,
                                    const InputInfoList &Inputs,
                                    const ArgList &Args,
                                    const char *LinkingOutput) const {
+  const Driver &D = getToolChain().getDriver();
   const bool IsPIE = getPIE(Args, getToolChain());
   ArgStringList CmdArgs;
 
@@ -152,8 +153,11 @@ void solaris::Linker::ConstructJob(Compilation &C, const JobAction &JA,
 
   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs,
                    options::OPT_r)) {
-    if (getToolChain().ShouldLinkCXXStdlib(Args))
-      getToolChain().AddCXXStdlibLibArgs(Args, CmdArgs);
+    if (D.CCCIsCXX()) {
+      if (getToolChain().ShouldLinkCXXStdlib(Args))
+        getToolChain().AddCXXStdlibLibArgs(Args, CmdArgs);
+      CmdArgs.push_back("-lm");
+    }
     if (Args.hasArg(options::OPT_fstack_protector) ||
         Args.hasArg(options::OPT_fstack_protector_strong) ||
         Args.hasArg(options::OPT_fstack_protector_all)) {
@@ -172,7 +176,6 @@ void solaris::Linker::ConstructJob(Compilation &C, const JobAction &JA,
     CmdArgs.push_back("-lc");
     if (!Args.hasArg(options::OPT_shared)) {
       CmdArgs.push_back("-lgcc");
-      CmdArgs.push_back("-lm");
     }
     const SanitizerArgs &SA = getToolChain().getSanitizerArgs(Args);
     if (NeedsSanitizerDeps) {
diff --git a/clang/test/Driver/solaris-ld.c b/clang/test/Driver/solaris-ld.c
index 8d97a5a3695b..a172fcb2e481 100644
--- a/clang/test/Driver/solaris-ld.c
+++ b/clang/test/Driver/solaris-ld.c
@@ -20,7 +20,6 @@
 // CHECK-LD-SPARC32-SAME: "-lgcc_s"
 // CHECK-LD-SPARC32-SAME: "-lc"
 // CHECK-LD-SPARC32-SAME: "-lgcc"
-// CHECK-LD-SPARC32-SAME: "-lm"
 // CHECK-LD-SPARC32-SAME: "[[SYSROOT]]/usr/gcc/4.8/lib/gcc/sparc-sun-solaris2.11/4.8.2{{/|\\\\}}crtend.o"
 // CHECK-LD-SPARC32-SAME: "[[SYSROOT]]/usr/lib{{/|\\\\}}crtn.o"
 
@@ -43,7 +42,6 @@
 // CHECK-LD-SPARC64-SAME: "-lgcc_s"
 // CHECK-LD-SPARC64-SAME: "-lc"
 // CHECK-LD-SPARC64-SAME: "-lgcc"
-// CHECK-LD-SPARC64-SAME: "-lm"
 // CHECK-LD-SPARC64-SAME: "[[SYSROOT]]/usr/gcc/4.8/lib/gcc/sparc-sun-solaris2.11/4.8.2/sparcv9{{/|\\\\}}crtend.o"
 // CHECK-LD-SPARC64-SAME: "[[SYSROOT]]/usr/lib/sparcv9{{/|\\\\}}crtn.o"
 
@@ -66,7 +64,6 @@
 // CHECK-LD-X32-SAME: "-lgcc_s"
 // CHECK-LD-X32-SAME: "-lc"
 // CHECK-LD-X32-SAME: "-lgcc"
-// CHECK-LD-X32-SAME: "-lm"
 // CHECK-LD-X32-SAME: "[[SYSROOT]]/usr/gcc/4.9/lib/gcc/i386-pc-solaris2.11/4.9.4{{/|\\\\}}crtend.o"
 // CHECK-LD-X32-SAME: "[[SYSROOT]]/usr/lib{{/|\\\\}}crtn.o"
 
@@ -90,7 +87,6 @@
 // CHECK-LD-X64-SAME: "-lgcc_s"
 // CHECK-LD-X64-SAME: "-lc"
 // CHECK-LD-X64-SAME: "-lgcc"
-// CHECK-LD-X64-SAME: "-lm"
 // CHECK-LD-X64-SAME: "[[SYSROOT]]/usr/gcc/4.9/lib/gcc/i386-pc-solaris2.11/4.9.4/amd64{{/|\\\\}}crtend.o"
 // CHECK-LD-X64-SAME: "[[SYSROOT]]/usr/lib/amd64{{/|\\\\}}crtn.o"
 
@@ -104,7 +100,22 @@
 // CHECK-SPARC32-SHARED-SAME: "-lgcc_s"
 // CHECK-SPARC32-SHARED-SAME: "-lc"
 // CHECK-SPARC32-SHARED-NOT: "-lgcc"
-// CHECK-SPARC32-SHARED-NOT: "-lm"
+
+// Check that libm is only linked with clang++.
+// RUN: %clang -### %s --target=sparc-sun-solaris2.11 \
+// RUN:     --gcc-toolchain="" --sysroot=%S/Inputs/solaris_sparc_tree 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NOLIBM %s
+// RUN: %clang -### %s -shared --target=sparc-sun-solaris2.11 \
+// RUN:     --gcc-toolchain="" --sysroot=%S/Inputs/solaris_sparc_tree 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NOLIBM %s
+// RUN: %clangxx -### %s --target=sparc-sun-solaris2.11 \
+// RUN:     --gcc-toolchain="" --sysroot=%S/Inputs/solaris_sparc_tree 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-LIBM %s
+// RUN: %clangxx -### %s -shared --target=sparc-sun-solaris2.11 \
+// RUN:     --gcc-toolchain="" --sysroot=%S/Inputs/solaris_sparc_tree 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-LIBM %s
+// CHECK-LIBM: "-lm"
+// CHECK-NOLIBM-NOT: "-lm"
 
 // Check the right ld flags are present with -pie.
 // RUN: %clang --target=sparc-sun-solaris2.11 -### %s -pie \