We need to end the basic block after the ##prologue in the dispatch branch so that the GC check can go after the prologue

basis/compiler/cfg/builder/builder.factor

@@ -171,6 +171,7 @@ M: #if emit-node
             [
                 V{ } clone node-stack set
                 ##prologue
+                begin-basic-block
                 emit-nodes
                 basic-block get [
                     ##epilogue

basis/compiler/tests/templates.factor

@@ -219,3 +219,14 @@ TUPLE: my-tuple ;
 : bad-value-bug ( a -- b ) [ 3 ] [ 3 ] if f <array> ;
 
 [ { f f f } ] [ t bad-value-bug ] unit-test
+
+! PowerPC regression
+TUPLE: id obj ;
+
+: (gc-check-bug) ( a b -- c )
+    { [ id boa ] [ id boa ] } dispatch ;
+
+: gc-check-bug ( -- )
+    10000000 [ "hi" 0 (gc-check-bug) drop ] times ;
+
+[ ] [ gc-check-bug ] unit-test