[clang] [FatLTO] Allow -fno-fat-lto-objects to override -ffat-lto-objects (PR #128157)

[via cfe-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang-driver

Author: Vincent Lee (thevinster)

<details>
<summary>Changes</summary>

For builds that cannot be easily modified and enabled with `-ffat-lto-objects`, `-fno-fat-lto-objects` acts as an escape hatch to disable this option (which is standard to how many clang and lld flags are used).

---
Full diff: https://github.com/llvm/llvm-project/pull/128157.diff


2 Files Affected:

- (modified) clang/lib/Driver/ToolChains/CommonArgs.cpp (+1-1) 
- (modified) clang/test/Driver/fat-lto-objects.c (+3) 


``````````diff
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index 1a2299a92c54e..50db1e2f7d509 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -860,7 +860,7 @@ void tools::addLTOOptions(const ToolChain &ToolChain, const ArgList &Args,
   const bool IsAMDGCN = Triple.isAMDGCN();
   const char *Linker = Args.MakeArgString(ToolChain.GetLinkerPath());
   const Driver &D = ToolChain.getDriver();
-  const bool IsFatLTO = Args.hasArg(options::OPT_ffat_lto_objects);
+  const bool IsFatLTO = Args.hasFlag(options::OPT_ffat_lto_objects, options::OPT_fno_fat_lto_objects, false);
   const bool IsUnifiedLTO = Args.hasArg(options::OPT_funified_lto);
   if (llvm::sys::path::filename(Linker) != "ld.lld" &&
       llvm::sys::path::stem(Linker) != "ld.lld" && !Triple.isOSOpenBSD()) {
diff --git a/clang/test/Driver/fat-lto-objects.c b/clang/test/Driver/fat-lto-objects.c
index d9a5ba88ea6d6..691fcbfc72140 100644
--- a/clang/test/Driver/fat-lto-objects.c
+++ b/clang/test/Driver/fat-lto-objects.c
@@ -41,6 +41,9 @@
 // CHECK-CC-NOLTO-SAME: -emit-obj
 // CHECK-CC-NOLTO-NOT: -ffat-lto-objects
 
+/// Disable fat LTO when it is overridden by -fno-fat-lto-objects
+// RUN: %clang --target=x86_64-unknown-linux-gnu -flto -ffat-lto-objects -fno-fat-lto-objects -### %s -c 2>&1 | FileCheck %s -check-prefix=CHECK-CC-NOLTO
+
 /// We need to pass an additional flag (--fat-lto-objects) to lld when linking w/ -flto -ffat-lto-objects
 /// But it should not be there when LTO is disabled w/ -fno-lto
 // RUN: %clang --target=x86_64-unknown-linux-gnu --sysroot=%S/Inputs/basic_cross_linux_tree %s \

``````````

</details>


https://github.com/llvm/llvm-project/pull/128157