[Driver] Allow -fbasic-block-sections for AArch64 ELF

[dhoekwater]

Basic block sections "all" doesn't work on AArch64 since branch
relaxation may create new basic blocks. However, the other basic
block section modes should work out of the box since machine function
splitting already uses the basic block sections pass.

[llvmbot]

@llvm/pr-subscribers-clang-driver

@llvm/pr-subscribers-clang

Author: Daniel Hoekwater (dhoekwater)

Changes

Basic block sections "all" doesn't work on AArch64 since branch
relaxation may create new basic blocks. However, the other basic
block section modes should work out of the box since machine function
splitting already uses the basic block sections pass.

---

Full diff: https://github.com/llvm/llvm-project/pull/80916.diff

2 Files Affected:

• (modified) clang/lib/Driver/ToolChains/Clang.cpp (+9)
• (modified) clang/test/Driver/fbasic-block-sections.c (+4)

diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 13bf2421154372..4a3fe7c5148b31 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -5972,6 +5972,15 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
             << A->getAsString(Args) << A->getValue();
       else
         A->render(Args, CmdArgs);
+    } else if (Triple.isAArch64()) {
+      // "all" is not supported on AArch64 since branch relaxation creates new
+      // basic blocks for some cross-section branches.
+      if (Val != "labels" && Val != "none" && !Val.starts_with("list="))
+        D.Diag(diag::err_drv_invalid_value)
+            << A->getAsString(Args) << A->getValue();
+      else
+        A->render(Args, CmdArgs);
+    }
     } else if (Triple.isNVPTX()) {
       // Do not pass the option to the GPU compilation. We still want it enabled
       // for the host-side compilation, so seeing it here is not an error.
diff --git a/clang/test/Driver/fbasic-block-sections.c b/clang/test/Driver/fbasic-block-sections.c
index 24262209d1e4d5..5e701072bfc74a 100644
--- a/clang/test/Driver/fbasic-block-sections.c
+++ b/clang/test/Driver/fbasic-block-sections.c
@@ -2,6 +2,10 @@
 // RUN: %clang -### --target=x86_64 -fbasic-block-sections=all %s -S 2>&1 | FileCheck -check-prefix=CHECK-OPT-ALL %s
 // RUN: %clang -### --target=x86_64 -fbasic-block-sections=list=%s %s -S 2>&1 | FileCheck -check-prefix=CHECK-OPT-LIST %s
 // RUN: %clang -### --target=x86_64 -fbasic-block-sections=labels %s -S 2>&1 | FileCheck -check-prefix=CHECK-OPT-LABELS %s
+// RUN: %clang -### --target=aarch64 -fbasic-block-sections=none %s -S 2>&1 | FileCheck -check-prefix=CHECK-OPT-NONE %s
+// RUN: %clang -### --target=aarch64 -fbasic-block-sections=list=%s %s -S 2>&1 | FileCheck -check-prefix=CHECK-OPT-LIST %s
+// RUN: %clang -### --target=aarch64 -fbasic-block-sections=labels %s -S 2>&1 | FileCheck -check-prefix=CHECK-OPT-LABELS %s
+// RUN: not %clang -### --target=aarch64 -fbasic-block-sections=all %s -S 2>&1 | FileCheck -check-prefix=CHECK-OPT-ALL %s
 // RUN: not %clang -c --target=arm-unknown-linux -fbasic-block-sections=all %s -S 2>&1 | FileCheck -check-prefix=CHECK-TRIPLE %s
 // RUN: %clang -### --target=arm-unknown-linux -fbasic-block-sections=all -fbasic-block-sections=none %s -S 2>&1 \
 // RUN:   | FileCheck -check-prefix=CHECK-NOOPT %s

[minglotus-6]

Optional suggestion to revise the title as something like 'Clang options for basic block sections on aarch64"

[MaskRay]

Perhaps `[Driver] Allow -fbasic-block-sections for ELF AArch64'