add a simple test

Author: paperchalice

llvm/test/CodeGen/X86/dag-combiner-fma-folding.ll

@@ -0,0 +1,22 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -mtriple=x86_64-- --start-before=x86-isel -mattr=+avx,+fma %s -o - | FileCheck %s
+
+define double @fma_folding(double %x) {
+; CHECK-LABEL: fma_folding:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vmovsd {{.*#+}} xmm0 = [1.0E+0,0.0E+0]
+; CHECK-NEXT:    retq
+ %prod = fmul contract ninf nnan double %x, 0.0
+ %fused = fadd contract ninf nnan double %prod, 1.0
+ ret double %fused
+}
+
+define double @fma_no_folding(double %x) {
+; CHECK-LABEL: fma_no_folding:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    vxorpd %xmm1, %xmm1, %xmm1
+; CHECK-NEXT:    vfmadd213sd {{.*#+}} xmm0 = (xmm1 * xmm0) + mem
+; CHECK-NEXT:    retq
+  %fused = call contract nnan ninf double @llvm.fma.f64(double %x, double 0.0, double -0.0)
+  ret double %fused
+}