cmd/compile: update WBLoads during deadcode

When we deadcode-remove a block which is a write barrier test,
remove that block from the list of write barrier test blocks.

Fixes #25516

Change-Id: I1efe732d5476003eab4ad6bf67d0340d7874ff0c
Reviewed-on: https://go-review.googlesource.com/115037
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/ssa/deadcode.go b/src/cmd/compile/internal/ssa/deadcode.go
index 322ea82c8d..13b7d7e1e8 100644
--- a/src/cmd/compile/internal/ssa/deadcode.go
+++ b/src/cmd/compile/internal/ssa/deadcode.go
@@ -252,6 +252,19 @@ func deadcode(f *Func) {
 		b.Values = b.Values[:i]
 	}
 
+	// Remove dead blocks from WBLoads list.
+	i = 0
+	for _, b := range f.WBLoads {
+		if reachable[b.ID] {
+			f.WBLoads[i] = b
+			i++
+		}
+	}
+	for j := i; j < len(f.WBLoads); j++ {
+		f.WBLoads[j] = nil
+	}
+	f.WBLoads = f.WBLoads[:i]
+
 	// Remove unreachable blocks. Return dead blocks to allocator.
 	i = 0
 	for _, b := range f.Blocks {