[llvm] [ARM] Emit an error when the hard-float ABI is enabled but can't be used. (PR #111334)

[Chris Copeland via llvm-commits]

https://github.com/chrisnc updated https://github.com/llvm/llvm-project/pull/111334

>From 06fede0c6bce33379560dc7719a114e23f5a0b7a Mon Sep 17 00:00:00 2001
From: Chris Copeland <chris at chrisnc.net>
Date: Sun, 23 Feb 2025 00:01:26 -0800
Subject: [PATCH] [ARM] Emit a warning when the hard-float ABI is enabled but
 can't be used.

Compiling for an eabihf target with a CPU lacking floating-point
registers will silently use the soft-float ABI instead, even though the
Arm attributes section still has Tag_ABI_VFP_args: VFP registers, which
leads to silent ABI mismatches at link time.

Fixes #110383.
---
 llvm/lib/Target/ARM/ARMISelLowering.cpp   |  4 +++-
 llvm/test/CodeGen/ARM/eabihf-no-fpregs.ll | 15 +++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/CodeGen/ARM/eabihf-no-fpregs.ll

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index c7ed73d0e95f7..c54db12379b71 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -791,7 +791,9 @@ ARMTargetLowering::ARMTargetLowering(const TargetMachine &TM,
       setAllExpand(MVT::f32);
     if (!Subtarget->hasFP64())
       setAllExpand(MVT::f64);
-  }
+  } else if (TM.Options.FloatABIType == FloatABI::Hard)
+    errs() << "The hard-float ABI can't be used for a target that "
+              "doesn't support floating-point (ignoring float-abi)\n";
 
   if (Subtarget->hasFullFP16()) {
     addRegisterClass(MVT::f16, &ARM::HPRRegClass);
diff --git a/llvm/test/CodeGen/ARM/eabihf-no-fpregs.ll b/llvm/test/CodeGen/ARM/eabihf-no-fpregs.ll
new file mode 100644
index 0000000000000..dbbf2f3ef0909
--- /dev/null
+++ b/llvm/test/CodeGen/ARM/eabihf-no-fpregs.ll
@@ -0,0 +1,15 @@
+; RUN: llc -asm-verbose=false --mtriple=armv7-none-eabihf --mattr=+vfp3 < %s | FileCheck %s --check-prefix=CHECK-VFP
+; RUN: llc -asm-verbose=false --mtriple=armv7-none-eabi --mattr=-fpregs < %s | FileCheck %s -check-prefix=CHECK-NOVFP
+; RUN: llc -asm-verbose=false --mtriple=armv7-none-eabihf --mattr=-fpregs < %s 2>&1 | FileCheck %s -check-prefix=CHECK-ERROR -check-prefix=CHECK-NOVFP
+
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-n32"
+
+; CHECK-VFP: vadd.f32
+; CHECK-ERROR: The hard-float ABI can't be used for a target that doesn't support floating-point (ignoring float-abi)
+; CHECK-NOVFP: bl __aeabi_fadd
+define float @test_fadd(float %a, float %b) #0 {
+  %r = fadd float %a, %b
+  ret float %r
+}
+
+attributes #0 = { nounwind }