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[ARM] Emit a warning when the hard-float ABI is enabled but can't be used. #111334

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[ARM] Emit a warning when the hard-float ABI is enabled but can't be used. #111334

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4 changes: 3 additions & 1 deletion llvm/lib/Target/ARM/ARMISelLowering.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -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)
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When I run this on a test program I get a couple of warnings

bin/clang --target=arm-none-eabihf -march=armv7-r nofp.c -c -mfloat-abi=hard -ffunction-sections
clang: warning: '-mfloat-abi=hard': selected processor lacks floating point registers [-Wunsupported-abi]
The hard-float ABI can't be used for a target that doesn't support floating-point (ignoring float-abi)
The hard-float ABI can't be used for a target that doesn't support floating-point (ignoring float-abi)

I think this is because this constructor is run once per ARMSubtarget. Tracing this back to getSubtargetImpl where ARMSubtargets are created https://github.com/llvm/llvm-project/blob/main/llvm/lib/Target/ARM/ARMTargetMachine.cpp#L280

It looks like that might be a better place to put this diagnostic. We may also want to see if some additional information like the function name can be used, possibly something from the Subtarget if the output is human readable.

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That does look like a better place for this, and already has one check like this, emitted through the LLVMContext so that the compiler can exit with a non-zero status code, or report the error through whatever other means it normally used. I think an error is better than a warning for this, because it's not possible to generate the requested code correctly.

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);
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15 changes: 15 additions & 0 deletions llvm/test/CodeGen/ARM/eabihf-no-fpregs.ll
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@@ -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 }