[clang] [clang][flang][windows] Prefer user-provided library paths (-L) (PR #90758)

[David Truby via cfe-commits]

https://github.com/DavidTruby created https://github.com/llvm/llvm-project/pull/90758

Currently the paths to compiler-rt and the Flang runtimes from the LLVM build/install directory are preferred over any user-provided library paths. This means a user can't override compiler-rt or the Flang runtimes with custom versions.

This patch changes the link order to prefer library paths specified with -L over the LLVM paths. This matches the behaviour of clang and flang on Linux.

>From 0afdbb7dac3a3a051661d5747c8c6470a13f1e0c Mon Sep 17 00:00:00 2001
From: David Truby <david at truby.dev>
Date: Wed, 1 May 2024 19:41:47 +0100
Subject: [PATCH] [clang][flang][windows] Prefer user-provided library paths
 (-L)

Currently the paths to compiler-rt and the Flang runtimes from the LLVM
build/install directory are preferred over any user-provided library
paths. This means a user can't override compiler-rt or the Flang
runtimes with custom versions.

This patch changes the link order to prefer library paths specified
with -L over the LLVM paths. This matches the behaviour of clang
and flang on Linux.
---
 clang/lib/Driver/ToolChains/MSVC.cpp | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/clang/lib/Driver/ToolChains/MSVC.cpp b/clang/lib/Driver/ToolChains/MSVC.cpp
index fbf2f45b543844..b7021d4b996ddd 100644
--- a/clang/lib/Driver/ToolChains/MSVC.cpp
+++ b/clang/lib/Driver/ToolChains/MSVC.cpp
@@ -134,6 +134,10 @@ void visualstudio::Linker::ConstructJob(Compilation &C, const JobAction &JA,
           Args.MakeArgString(std::string("-libpath:") + WindowsSdkLibPath));
   }
 
+  if (!C.getDriver().IsCLMode() && Args.hasArg(options::OPT_L))
+    for (const auto &LibPath : Args.getAllArgValues(options::OPT_L))
+      CmdArgs.push_back(Args.MakeArgString("-libpath:" + LibPath));
+
   if (C.getDriver().IsFlangMode()) {
     addFortranRuntimeLibraryPath(TC, Args, CmdArgs);
     addFortranRuntimeLibs(TC, Args, CmdArgs);
@@ -154,10 +158,6 @@ void visualstudio::Linker::ConstructJob(Compilation &C, const JobAction &JA,
   if (TC.getVFS().exists(CRTPath))
     CmdArgs.push_back(Args.MakeArgString("-libpath:" + CRTPath));
 
-  if (!C.getDriver().IsCLMode() && Args.hasArg(options::OPT_L))
-    for (const auto &LibPath : Args.getAllArgValues(options::OPT_L))
-      CmdArgs.push_back(Args.MakeArgString("-libpath:" + LibPath));
-
   CmdArgs.push_back("-nologo");
 
   if (Args.hasArg(options::OPT_g_Group, options::OPT__SLASH_Z7))