[clang] [flang] [clang][driver] Fix -fveclib=ArmPL issue: with -nostdlib do not link against libm (PR #133578)

[Paul Osmialowski via cfe-commits]

================
@@ -515,17 +515,19 @@ 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"));
----------------
pawosm-arm wrote:

There was a very long story behind this which has been discussed while this code has been introduced. In short: libamath replaces some of the libm functions, but at the same time, some of the libamath functions depend on libm. In this case, we don't want to outshadow libm (we only want to provide vector implementations on as-needed basis), and at the same time we want to produce a valid binary with no missing symbols (and that's wehre libm is needed) as long as no `-nostdlib` flag is given.


https://github.com/llvm/llvm-project/pull/133578