[Downstream change][clang][driver] Fix -fveclib=ArmPL issue: with -nostdlib do not link against libm (#245)

It's a cherry-pick from the arm-software branch.

Downstream issue: #242

Although combining -fveclib=ArmPL with -nostdlib is a rare situation, it
should still be supported correctly and should effect in avoidance of
linking against libm.

Author: pawosm-arm

clang/lib/Driver/ToolChains/CommonArgs.cpp

@@ -511,17 +511,19 @@ void tools::AddLinkerInputs(const ToolChain &TC, const InputInfoList &Inputs,
       //
       // 1. On Linux, link only when actually needed.
       //
-      // 2. Prefer libm functions over libamath.
+      // 2. Prefer libm functions over libamath (when no -nostdlib in use).
       //
       // 3. Link against libm to resolve libamath dependencies.
       //
       if (Triple.isOSLinux()) {
         CmdArgs.push_back(Args.MakeArgString("--push-state"));
         CmdArgs.push_back(Args.MakeArgString("--as-needed"));
       }
-      CmdArgs.push_back(Args.MakeArgString("-lm"));
+      if (!Args.hasArg(options::OPT_nostdlib))
+        CmdArgs.push_back(Args.MakeArgString("-lm"));
       CmdArgs.push_back(Args.MakeArgString("-lamath"));
-      CmdArgs.push_back(Args.MakeArgString("-lm"));
+      if (!Args.hasArg(options::OPT_nostdlib))
+        CmdArgs.push_back(Args.MakeArgString("-lm"));
       if (Triple.isOSLinux())
         CmdArgs.push_back(Args.MakeArgString("--pop-state"));
       addArchSpecificRPath(TC, Args, CmdArgs);

clang/test/Driver/fveclib.c

@@ -116,11 +116,17 @@
 /// Verify that vectorized routines library is being linked in.
 // RUN: %clang -### --target=aarch64-pc-windows-msvc -fveclib=ArmPL %s 2>&1 | FileCheck --check-prefix=CHECK-LINKING-ARMPL-MSVC %s
 // RUN: %clang -### --target=aarch64-linux-gnu -fveclib=ArmPL %s 2>&1 | FileCheck --check-prefix=CHECK-LINKING-ARMPL-LINUX %s
+// RUN: %clang -### --target=aarch64-linux-gnu -fveclib=ArmPL %s -nostdlib 2>&1 | FileCheck --check-prefix=CHECK-LINKING-ARMPL-NOSTDLIB-LINUX %s
 // RUN: %clang -### --target=aarch64-linux-gnu -fveclib=ArmPL %s -lamath 2>&1 | FileCheck --check-prefix=CHECK-LINKING-AMATH-BEFORE-ARMPL-LINUX %s
 // RUN: %clang -### --target=arm64-apple-darwin -fveclib=ArmPL %s 2>&1 | FileCheck --check-prefix=CHECK-LINKING-ARMPL-DARWIN %s
+// RUN: %clang -### --target=arm64-apple-darwin -fveclib=ArmPL -nostdlib %s 2>&1 | FileCheck --check-prefix=CHECK-LINKING-ARMPL-NOSTDLIB-DARWIN %s
 // RUN: %clang -### --target=arm64-apple-darwin -fveclib=ArmPL %s -lamath 2>&1 | FileCheck --check-prefix=CHECK-LINKING-AMATH-BEFORE-ARMPL-DARWIN %s
 // CHECK-LINKING-ARMPL-LINUX: "--push-state" "--as-needed" "-lm" "-lamath" "-lm" "--pop-state"
+// CHECK-LINKING-ARMPL-NOSTDLIB-LINUX: "--push-state" "--as-needed" "-lamath" "--pop-state"
+// CHECK-LINKING-ARMPL-NOSTDLIB-LINUX-NOT: "-lm"
 // CHECK-LINKING-ARMPL-DARWIN: "-lm" "-lamath" "-lm"
+// CHECK-LINKING-ARMPL-NOSTDLIB-DARWIN: "-lamath"
+// CHECK-LINKING-ARMPL-NOSTDLIB-DARWIN-NOT: "-lm"
 // CHECK-LINKING-ARMPL-MSVC: "--dependent-lib=amath"
 // CHECK-LINKING-AMATH-BEFORE-ARMPL-LINUX: "-lamath" {{.*}}"--push-state" "--as-needed" "-lm" "-lamath" "-lm" "--pop-state"
 // CHECK-LINKING-AMATH-BEFORE-ARMPL-DARWIN: "-lamath" {{.*}}"-lm" "-lamath" "-lm"

flang/test/Driver/fveclib.f90

@@ -33,11 +33,17 @@
 
 ! RUN: %flang -### --target=aarch64-pc-windows-msvc -fveclib=ArmPL %s 2>&1 | FileCheck --check-prefix=CHECK-LINKING-ARMPL-MSVC %s
 ! RUN: %flang -### --target=aarch64-linux-gnu -fveclib=ArmPL %s 2>&1 | FileCheck --check-prefix=CHECK-LINKING-ARMPL-LINUX %s
+! RUN: %flang -### --target=aarch64-linux-gnu -fveclib=ArmPL -nostdlib %s 2>&1 | FileCheck --check-prefix=CHECK-LINKING-ARMPL-NOSTDLIB-LINUX %s
 ! RUN: %flang -### --target=aarch64-linux-gnu -fveclib=ArmPL %s -lamath 2>&1 | FileCheck --check-prefix=CHECK-LINKING-AMATH-BEFORE-ARMPL-LINUX %s
 ! RUN: %flang -### --target=arm64-apple-darwin -fveclib=ArmPL %s 2>&1 | FileCheck --check-prefix=CHECK-LINKING-ARMPL-DARWIN %s
+! RUN: %flang -### --target=arm64-apple-darwin -fveclib=ArmPL -nostdlib %s 2>&1 | FileCheck --check-prefix=CHECK-LINKING-ARMPL-NOSTDLIB-DARWIN %s
 ! RUN: %flang -### --target=arm64-apple-darwin -fveclib=ArmPL %s -lamath 2>&1 | FileCheck --check-prefix=CHECK-LINKING-AMATH-BEFORE-ARMPL-DARWIN %s
 ! CHECK-LINKING-ARMPL-LINUX: "--push-state" "--as-needed" "-lm" "-lamath" "-lm" "--pop-state"
+! CHECK-LINKING-ARMPL-NOSTDLIB-LINUX: "--push-state" "--as-needed" "-lamath" "--pop-state"
+! CHECK-LINKING-ARMPL-NOSTDLIB-LINUX-NOT: "-lm"
 ! CHECK-LINKING-ARMPL-DARWIN: "-lm" "-lamath" "-lm"
+! CHECK-LINKING-ARMPL-NOSTDLIB-DARWIN: "-lamath"
+! CHECK-LINKING-ARMPL-NOSTDLIB-DARWIN-NOT: "-lm"
 ! CHECK-LINKING-ARMPL-MSVC: "--dependent-lib=amath"
 ! CHECK-LINKING-AMATH-BEFORE-ARMPL-LINUX: "-lamath" {{.*}}"--push-state" "--as-needed" "-lm" "-lamath" "-lm" "--pop-state"
 ! CHECK-LINKING-AMATH-BEFORE-ARMPL-DARWIN: "-lamath" {{.*}}"-lm" "-lamath" "-lm"