cmd/vet: add test for loading complex values with a single instruction

Actual fix will be submitted to x/tools and vendored.
This is just an end-to-end test for vet after that is done.

Update #35264

Change-Id: I1a63f607e7cfa7aafee23c2c081086c276d3c38c
Reviewed-on: https://go-review.googlesource.com/c/go/+/204538
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Alan Donovan <adonovan@google.com>

src/cmd/vet/testdata/asm/asm.go

@@ -7,3 +7,5 @@
 package testdata
 
 func arg1(x int8, y uint8)
+
+func cpx(x complex64, y complex128)

src/cmd/vet/testdata/asm/asm1.s

@@ -6,3 +6,18 @@
 
 TEXT ·arg1(SB),0,$0-2
 	MOVW	x+0(FP), AX // ERROR "\[amd64\] arg1: invalid MOVW of x\+0\(FP\); int8 is 1-byte value"
+
+TEXT ·cpx(SB),0,$0-24
+	// These are ok
+	MOVSS	x_real+0(FP), X0
+	MOVSS	x_imag+4(FP), X0
+	MOVSD	y_real+8(FP), X0
+	MOVSD	y_imag+16(FP), X0
+	// Loading both parts of a complex is ok: see issue 35264.
+	MOVSD	x+0(FP), X0
+	MOVO	y+8(FP), X0
+	MOVOU	y+8(FP), X0
+
+	// These are not ok.
+	MOVO	x+0(FP), X0 // ERROR "\[amd64\] cpx: invalid MOVO of x\+0\(FP\); complex64 is 8-byte value containing x_real\+0\(FP\) and x_imag\+4\(FP\)"
+	MOVSD	y+8(FP), X0 // ERROR "\[amd64\] cpx: invalid MOVSD of y\+8\(FP\); complex128 is 16-byte value containing y_real\+8\(FP\) and y_imag\+16\(FP\)"