[clang] [Driver] Default LoongArch to -fno-direct-access-external-data for non-PIC (PR #72221)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang-driver

@llvm/pr-subscribers-clang

Author: Fangrui Song (MaskRay)

<details>
<summary>Changes</summary>

For -fno-pic, if an extern variable is defined in a DSO, a copy
relocation will be needed. However, loongarch*-linux does not and will
not support copy relocations.

Change Driver to default to -fno-direct-access-external-data for
LoongArch && non-PIC.
Keep Frontend conditions unchanged (-fdirect-access-external-data ||
-fno-direct-access-external-data && PIC>0 => direct access).

Fix #<!-- -->71645


---
Full diff: https://github.com/llvm/llvm-project/pull/72221.diff


2 Files Affected:

- (modified) clang/lib/Driver/ToolChains/Clang.cpp (+6-1) 
- (modified) clang/test/Driver/fdirect-access-external-data.c (+6) 


``````````diff
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 3b98c7ae6e6ec66..b462f5a44057d94 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -5663,10 +5663,15 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
   // defaults to -fno-direct-access-external-data. Pass the option if different
   // from the default.
   if (Arg *A = Args.getLastArg(options::OPT_fdirect_access_external_data,
-                               options::OPT_fno_direct_access_external_data))
+                               options::OPT_fno_direct_access_external_data)) {
     if (A->getOption().matches(options::OPT_fdirect_access_external_data) !=
         (PICLevel == 0))
       A->render(Args, CmdArgs);
+  } else if (PICLevel == 0 && Triple.isLoongArch()) {
+    // Some targets default to -fno-direct-access-external-data even for
+    // -fno-pic.
+    CmdArgs.push_back("-fno-direct-access-external-data");
+  }
 
   if (Args.hasFlag(options::OPT_fno_plt, options::OPT_fplt, false)) {
     CmdArgs.push_back("-fno-plt");
diff --git a/clang/test/Driver/fdirect-access-external-data.c b/clang/test/Driver/fdirect-access-external-data.c
index f132b1b088af35d..a6da776e6977742 100644
--- a/clang/test/Driver/fdirect-access-external-data.c
+++ b/clang/test/Driver/fdirect-access-external-data.c
@@ -9,6 +9,12 @@
 // RUN: %clang -### -c -target aarch64 %s -fpic 2>&1 | FileCheck %s --check-prefix=DEFAULT
 // RUN: %clang -### -c -target aarch64 %s -fpic -fdirect-access-external-data 2>&1 | FileCheck %s --check-prefix=DIRECT
 
+/// loongarch* targets default to -fno-direct-access-external-data even for -fno-pic.
+// RUN: %clang -### -c --target=loongarch64 -fno-pic %s 2>&1 | FileCheck %s --check-prefix=INDIRECT
+// RUN: %clang -### -c --target=loongarch64 -fpie %s 2>&1 | FileCheck %s --check-prefix=DEFAULT
+// RUN: %clang -### -c --target=loongarch32 -fno-pic -fdirect-access-external-data %s 2>&1 | FileCheck %s --check-prefix=DEFAULT
+// RUN: %clang -### -c --target=loongarch32 -fpie -fdirect-access-external-data %s 2>&1 | FileCheck %s --check-prefix=DIRECT
+
 // DEFAULT-NOT: direct-access-external-data"
 // DIRECT:      "-fdirect-access-external-data"
 // INDIRECT:    "-fno-direct-access-external-data"

``````````

</details>


https://github.com/llvm/llvm-project/pull/72221