[clang] Fix coverage when /fo is used (PR #88201)

[via cfe-commits]

https://github.com/pdagobert created https://github.com/llvm/llvm-project/pull/88201

Fixes https://github.com/llvm/llvm-project/issues/87304

>From 6db0e01e198de9e5ee4055f9433150818c429c10 Mon Sep 17 00:00:00 2001
From: pdagobert <pdagobert at users.noreply.github.com>
Date: Tue, 9 Apr 2024 23:10:58 +0200
Subject: [PATCH] Fix coverage when /fo is used

---
 clang/lib/Driver/ToolChains/Clang.cpp | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 766a9b91e3c0ad..44d18acd25a589 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -802,6 +802,10 @@ static void addPGOAndCoverageFlags(const ToolChain &TC, Compilation &C,
     } else if (Arg *FinalOutput =
                    C.getArgs().getLastArg(options::OPT__SLASH_Fo)) {
       CoverageFilename = FinalOutput->getValue();
+      StringRef V = FinalOutput->getValue();
+      if (llvm::sys::path::is_separator(V.back())) {
+        CoverageFilename += llvm::sys::path::filename(Output.getBaseInput());
+      }
     } else if (Arg *FinalOutput = C.getArgs().getLastArg(options::OPT_o)) {
       CoverageFilename = FinalOutput->getValue();
     } else {