[LTO] Fix Veclib flags correctly pass to LTO flags (llvm#78749)

Flags `-fveclib=name` were not passed to LTO flags.
This pass fixes that by converting the `-fveclib` flags to their
relevant names for opt's `-vector-lib=name` flags.

For example:
`-fveclib=SLEEF` would become `-vector-library=sleefgnuabi` and passed
through the `-plugin-opt` flag.

Author: paschalis-mpeis

clang/lib/Driver/ToolChains/CommonArgs.cpp

@@ -781,6 +781,28 @@ void tools::addLTOOptions(const ToolChain &ToolChain, const ArgList &Args,
                                          "-generate-arange-section"));
   }
 
+  // Pass vector library arguments to LTO.
+  Arg *ArgVecLib = Args.getLastArg(options::OPT_fveclib);
+  if (ArgVecLib && ArgVecLib->getNumValues() == 1) {
+    // Map the vector library names from clang front-end to opt front-end. The
+    // values are taken from the TargetLibraryInfo class command line options.
+    std::optional<StringRef> OptVal =
+        llvm::StringSwitch<std::optional<StringRef>>(ArgVecLib->getValue())
+            .Case("Accelerate", "Accelerate")
+            .Case("LIBMVEC", "LIBMVEC-X86")
+            .Case("MASSV", "MASSV")
+            .Case("SVML", "SVML")
+            .Case("SLEEF", "sleefgnuabi")
+            .Case("Darwin_libsystem_m", "Darwin_libsystem_m")
+            .Case("ArmPL", "ArmPL")
+            .Case("none", "none")
+            .Default(std::nullopt);
+
+    if (OptVal)
+      CmdArgs.push_back(Args.MakeArgString(
+          Twine(PluginOptPrefix) + "-vector-library=" + OptVal.value()));
+  }
+
   // Try to pass driver level flags relevant to LTO code generation down to
   // the plugin.
 

clang/test/Driver/fveclib.c

@@ -31,3 +31,21 @@
 
 // RUN: %clang -fveclib=Accelerate %s -nodefaultlibs -target arm64-apple-ios8.0.0 -### 2>&1 | FileCheck --check-prefix=CHECK-LINK-NODEFAULTLIBS %s
 // CHECK-LINK-NODEFAULTLIBS-NOT: "-framework" "Accelerate"
+
+
+/* Verify that the correct vector library is passed to LTO flags. */
+
+// RUN: %clang -### --target=x86_64-unknown-linux-gnu -fveclib=LIBMVEC -flto %s 2>&1 | FileCheck -check-prefix CHECK-LTO-LIBMVEC %s
+// CHECK-LTO-LIBMVEC: "-plugin-opt=-vector-library=LIBMVEC-X86"
+
+// RUN: %clang -### --target=powerpc64-unknown-linux-gnu -fveclib=MASSV -flto %s 2>&1 | FileCheck -check-prefix CHECK-LTO-MASSV %s
+// CHECK-LTO-MASSV: "-plugin-opt=-vector-library=MASSV"
+
+// RUN: %clang -### --target=x86_64-unknown-linux-gnu -fveclib=SVML -flto %s 2>&1 | FileCheck -check-prefix CHECK-LTO-SVML %s
+// CHECK-LTO-SVML: "-plugin-opt=-vector-library=SVML"
+
+// RUN: %clang -### --target=aarch64-linux-gnu -fveclib=SLEEF -flto %s 2>&1 | FileCheck -check-prefix CHECK-LTO-SLEEF %s
+// CHECK-LTO-SLEEF: "-plugin-opt=-vector-library=sleefgnuabi"
+
+// RUN: %clang -### --target=aarch64-linux-gnu -fveclib=ArmPL -flto %s 2>&1 | FileCheck -check-prefix CHECK-LTO-ARMPL %s
+// CHECK-LTO-ARMPL: "-plugin-opt=-vector-library=ArmPL"