[SelectionDAG][X86] Add floating point promotion.

When lowering atomic vector types with floats, selection can fail since
this pattern is unsupported. To support this, floats can be casted to
an integer type of the same size.

Author: jofrn

Diff for: llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -2589,6 +2589,10 @@ X86TargetLowering::X86TargetLowering(const X86TargetMachine &TM,
         setOperationAction(Op, MVT::f32, Promote);
   }
 
+  setOperationPromotedToType(ISD::ATOMIC_LOAD, MVT::f16, MVT::i16);
+  setOperationPromotedToType(ISD::ATOMIC_LOAD, MVT::f32, MVT::i32);
+  setOperationPromotedToType(ISD::ATOMIC_LOAD, MVT::f64, MVT::i64);
+
   // We have target-specific dag combine patterns for the following nodes:
   setTargetDAGCombine({ISD::VECTOR_SHUFFLE,
                        ISD::SCALAR_TO_VECTOR,

Diff for: llvm/test/CodeGen/X86/atomic-scalarization.ll

@@ -10,6 +10,25 @@ define <1 x i32> @atomic_scalar_i32(ptr %x) {
   ret <1 x i32> %ret
 }
 
+define <1 x float> @atomic_scalar_float(ptr %x) {
+; CHECK-LABEL: atomic_scalar_float:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movss {{.*#+}} xmm0 = mem[0],zero,zero,zero
+; CHECK-NEXT:    retq
+  %ret = load atomic <1 x float>, ptr %x acquire, align 4
+  ret <1 x float> %ret
+}
+
+define <1 x half> @atomic_scalar_half(ptr %x) {
+; CHECK-LABEL: atomic_scalar_half:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    movzwl (%rdi), %eax
+; CHECK-NEXT:    pinsrw $0, %eax, %xmm0
+; CHECK-NEXT:    retq
+  %ret = load atomic <1 x half>, ptr %x acquire, align 4
+  ret <1 x half> %ret
+}
+
 define <1 x bfloat> @atomic_scalar_bfloat(ptr %x) {
 ; CHECK-LABEL: atomic_scalar_bfloat:
 ; CHECK:       # %bb.0: