[llvm] [ARM] Allow s constraints on half (PR #157860)

[Nikita Popov via llvm-commits]

https://github.com/nikic created https://github.com/llvm/llvm-project/pull/157860

Fix a regression from https://github.com/llvm/llvm-project/pull/147559.

>From 730dbfa6d546cf5f7d8ab546dda784896296efaf Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Wed, 10 Sep 2025 15:42:41 +0200
Subject: [PATCH] [ARM] Allow s constraints on half

Fix a regression from https://github.com/llvm/llvm-project/pull/147559.
---
 llvm/lib/Target/ARM/ARMISelLowering.cpp    |  8 ++-
 llvm/test/CodeGen/ARM/inlineasm-fp-half.ll | 77 ++++++++++++++++++++++
 2 files changed, 82 insertions(+), 3 deletions(-)

diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp
index d4d3c70095279..4af2721562d7c 100644
--- a/llvm/lib/Target/ARM/ARMISelLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp
@@ -20304,9 +20304,11 @@ ARMTargetLowering::getSingleConstraintMatchWeight(
 static bool isIncompatibleReg(const MCPhysReg &PR, MVT VT) {
   if (PR == 0 || VT == MVT::Other)
     return false;
-  return (ARM::SPRRegClass.contains(PR) && VT != MVT::f32 && VT != MVT::i32) ||
-         (ARM::DPRRegClass.contains(PR) && VT != MVT::f64 &&
-          !VT.is64BitVector());
+  if (ARM::SPRRegClass.contains(PR))
+    return VT != MVT::f32 && VT != MVT::f16 && VT != MVT::i32;
+  if (ARM::DPRRegClass.contains(PR))
+    return VT != MVT::f64 && !VT.is64BitVector();
+  return false;
 }
 
 using RCPair = std::pair<unsigned, const TargetRegisterClass *>;
diff --git a/llvm/test/CodeGen/ARM/inlineasm-fp-half.ll b/llvm/test/CodeGen/ARM/inlineasm-fp-half.ll
index 554e5ba72c5d4..1a0b2246f23f5 100644
--- a/llvm/test/CodeGen/ARM/inlineasm-fp-half.ll
+++ b/llvm/test/CodeGen/ARM/inlineasm-fp-half.ll
@@ -495,3 +495,80 @@ entry:
   %0 = tail call bfloat asm "vmov $0, $1", "=x,x"(bfloat %x)
   ret bfloat %0
 }
+
+define half @half_s(half %x) nounwind {
+; NO-FP16-SOFTFP-LABEL: half_s:
+; NO-FP16-SOFTFP:       @ %bb.0: @ %entry
+; NO-FP16-SOFTFP-NEXT:    vmov s2, r0
+; NO-FP16-SOFTFP-NEXT:    @APP
+; NO-FP16-SOFTFP-NEXT:    vmov.f32 s1, s2
+; NO-FP16-SOFTFP-NEXT:    @NO_APP
+; NO-FP16-SOFTFP-NEXT:    vmov r0, s1
+; NO-FP16-SOFTFP-NEXT:    bx lr
+;
+; NO-FP16-HARD-LABEL: half_s:
+; NO-FP16-HARD:       @ %bb.0: @ %entry
+; NO-FP16-HARD-NEXT:    vmov.f32 s2, s0
+; NO-FP16-HARD-NEXT:    @APP
+; NO-FP16-HARD-NEXT:    vmov.f32 s1, s2
+; NO-FP16-HARD-NEXT:    @NO_APP
+; NO-FP16-HARD-NEXT:    vmov.f32 s0, s1
+; NO-FP16-HARD-NEXT:    bx lr
+;
+; FP16-SOFTFP-LABEL: half_s:
+; FP16-SOFTFP:       @ %bb.0: @ %entry
+; FP16-SOFTFP-NEXT:    vmov.f16 s2, r0
+; FP16-SOFTFP-NEXT:    @APP
+; FP16-SOFTFP-NEXT:    vmov.f32 s1, s2
+; FP16-SOFTFP-NEXT:    @NO_APP
+; FP16-SOFTFP-NEXT:    vmov r0, s1
+; FP16-SOFTFP-NEXT:    bx lr
+;
+; FP16-HARD-LABEL: half_s:
+; FP16-HARD:       @ %bb.0: @ %entry
+; FP16-HARD-NEXT:    vmov.f32 s2, s0
+; FP16-HARD-NEXT:    @APP
+; FP16-HARD-NEXT:    vmov.f32 s1, s2
+; FP16-HARD-NEXT:    @NO_APP
+; FP16-HARD-NEXT:    vmov.f32 s0, s1
+; FP16-HARD-NEXT:    bx lr
+;
+; BF16-SOFTFP-LABEL: half_s:
+; BF16-SOFTFP:       @ %bb.0: @ %entry
+; BF16-SOFTFP-NEXT:    vmov.f16 s2, r0
+; BF16-SOFTFP-NEXT:    @APP
+; BF16-SOFTFP-NEXT:    vmov.f32 s1, s2
+; BF16-SOFTFP-NEXT:    @NO_APP
+; BF16-SOFTFP-NEXT:    vmov r0, s1
+; BF16-SOFTFP-NEXT:    bx lr
+;
+; SIMD-BF16-SOFTFP-LABEL: half_s:
+; SIMD-BF16-SOFTFP:       @ %bb.0: @ %entry
+; SIMD-BF16-SOFTFP-NEXT:    vmov.f16 s2, r0
+; SIMD-BF16-SOFTFP-NEXT:    @APP
+; SIMD-BF16-SOFTFP-NEXT:    vmov.f32 s1, s2
+; SIMD-BF16-SOFTFP-NEXT:    @NO_APP
+; SIMD-BF16-SOFTFP-NEXT:    vmov r0, s1
+; SIMD-BF16-SOFTFP-NEXT:    bx lr
+;
+; BF16-HARD-LABEL: half_s:
+; BF16-HARD:       @ %bb.0: @ %entry
+; BF16-HARD-NEXT:    vmov.f32 s2, s0
+; BF16-HARD-NEXT:    @APP
+; BF16-HARD-NEXT:    vmov.f32 s1, s2
+; BF16-HARD-NEXT:    @NO_APP
+; BF16-HARD-NEXT:    vmov.f32 s0, s1
+; BF16-HARD-NEXT:    bx lr
+;
+; SIMD-BF16-HARD-LABEL: half_s:
+; SIMD-BF16-HARD:       @ %bb.0: @ %entry
+; SIMD-BF16-HARD-NEXT:    vmov.f32 s2, s0
+; SIMD-BF16-HARD-NEXT:    @APP
+; SIMD-BF16-HARD-NEXT:    vmov.f32 s1, s2
+; SIMD-BF16-HARD-NEXT:    @NO_APP
+; SIMD-BF16-HARD-NEXT:    vmov.f32 s0, s1
+; SIMD-BF16-HARD-NEXT:    bx lr
+entry:
+  %0 = tail call half asm "vmov $0, $1", "={s1},{s2}"(half %x)
+  ret half %0
+}