cmd/compile: schedule values with no in-block uses later

When scheduling a block, deprioritize values whose results aren't used
until subsequent blocks.

For #58166, this has the effect of pushing the induction variable increment
to the end of the block, past all the other uses of the pre-incremented value.

Do this only with optimizations on. Debuggers have a preference for values
in source code order, which this CL can degrade.

Fixes #58166
Fixes #57976

Change-Id: I40d5885c661b142443c6d4702294c8abe8026c4f
Reviewed-on: https://go-review.googlesource.com/c/go/+/463751
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Keith Randall <khr@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/test/codegen/issue58166.go b/test/codegen/issue58166.go
new file mode 100644
index 0000000000..8be5aac841
--- /dev/null
+++ b/test/codegen/issue58166.go
@@ -0,0 +1,23 @@
+// asmcheck
+
+// Copyright 2023 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package p
+
+func dgemmSerialNotNot(m, n, k int, a []float64, lda int, b []float64, ldb int, c []float64, ldc int, alpha float64) {
+	for i := 0; i < m; i++ {
+		ctmp := c[i*ldc : i*ldc+n]
+		for l, v := range a[i*lda : i*lda+k] {
+			tmp := alpha * v
+			if tmp != 0 {
+				x := b[l*ldb : l*ldb+n]
+				// amd64:"INCQ"
+				for i, v := range x {
+					ctmp[i] += tmp * v
+				}
+			}
+		}
+	}
+}