compiler: add support for complex add and sub

This is fairly trivial to add and follows the implementation of gc:
170b8b4b12/src/cmd/compile/internal/gc/ssa.go (L2179-L2192)

compiler/compiler.go

@@ -1821,6 +1821,22 @@ func (c *Compiler) parseBinOp(op token.Token, typ types.Type, x, y llvm.Value, p
 				ieq := c.builder.CreateFCmp(llvm.FloatOEQ, i1, i2, "")
 				neq := c.builder.CreateAnd(req, ieq, "")
 				return c.builder.CreateNot(neq, ""), nil
+			case token.ADD, token.SUB:
+				var r, i llvm.Value
+				switch op {
+				case token.ADD:
+					r = c.builder.CreateFAdd(r1, r2, "")
+					i = c.builder.CreateFAdd(i1, i2, "")
+				case token.SUB:
+					r = c.builder.CreateFSub(r1, r2, "")
+					i = c.builder.CreateFSub(i1, i2, "")
+				default:
+					panic("unreachable")
+				}
+				cplx := llvm.Undef(c.ctx.StructType([]llvm.Type{r.Type(), i.Type()}, false))
+				cplx = c.builder.CreateInsertValue(cplx, r, 0, "")
+				cplx = c.builder.CreateInsertValue(cplx, i, 1, "")
+				return cplx, nil
 			default:
 				return llvm.Value{}, c.makeError(pos, "todo: binop on complex number: "+op.String())
 			}

testdata/float.go

@@ -56,4 +56,12 @@ func main() {
 	// cast complex
 	println(complex64(c128))
 	println(complex128(c64))
+
+	// binops on complex numbers
+	c64 = 5+2i
+	println("complex64 add: ", c64 + -3+8i)
+	println("complex64 sub: ", c64 - -3+8i)
+	c128 = -5+2i
+	println("complex128 add:", c128 + 2+6i)
+	println("complex128 sub:", c128 - 2+6i)
 }

testdata/float.txt

@@ -23,3 +23,7 @@
 (+2.000000e+000-2.000000e+000i)
 (+6.666667e-001-2.000000e+000i)
 (+6.666667e-001+1.200000e+000i)
+complex64 add:  (+2.000000e+000+1.000000e+001i)
+complex64 sub:  (+8.000000e+000+1.000000e+001i)
+complex128 add: (-3.000000e+000+8.000000e+000i)
+complex128 sub: (-7.000000e+000+8.000000e+000i)