[dev.ssa] cmd/compile/internal/ssa: fix sign extension + load combo

Load-and-sign-extend opcodes were being generated in the
wrong block, leading to having more than one memory variable
live at once.  Fix the rules + add a test.

Change-Id: Iadf80e55ea901549c15c628ae295c2d0f1f64525
Reviewed-on: https://go-review.googlesource.com/14591
Reviewed-by: Todd Neal <todd@tneal.org>
Run-TryBot: Todd Neal <todd@tneal.org>

1 files changed, 21 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/gc/testdata/loadstore_ssa.go b/src/cmd/compile/internal/gc/testdata/loadstore_ssa.go
index cf37095742..e986f53bc6 100644
--- a/src/cmd/compile/internal/gc/testdata/loadstore_ssa.go
+++ b/src/cmd/compile/internal/gc/testdata/loadstore_ssa.go
@@ -57,10 +57,31 @@ func testStoreSize_ssa(p *uint16, q *uint16, v uint32) {
 
 var failed = false
 
+func testExtStore_ssa(p *byte, b bool) int {
+	switch {
+	}
+	x := *p
+	*p = 7
+	if b {
+		return int(x)
+	}
+	return 0
+}
+
+func testExtStore() {
+	const start = 8
+	var b byte = start
+	if got := testExtStore_ssa(&b, true); got != start {
+		fmt.Println("testExtStore failed.  want =", start, ", got =", got)
+		failed = true
+	}
+}
+
 func main() {
 
 	testLoadStoreOrder()
 	testStoreSize()
+	testExtStore()
 
 	if failed {
 		panic("failed")