Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
---
ptrlist.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/ptrlist.c b/ptrlist.c
index 3af0b2c5fbaa..0f0b3f6d818f 100644
--- a/ptrlist.c
+++ b/ptrlist.c
@@ -7,6 +7,18 @@
///
// Pointer list manipulation
// -------------------------
+//
+// The data structure handled here is designed to hold pointers
+// but two special cases need to be avoided or need special care:
+// * NULL is used by {PREPARE,NEXT}_PTR_LIST() to indicate the end-of-list.
+// Thus, NULL can't be stored in lists using this API but is fine to
+// use with FOR_EACH_PTR() and its variants.
+// * VOID is used to replace a removed pseudo 'usage'. Since phi-nodes
+// (OP_PHI) use a list to store their operands, a VOID in a phi-node
+// list must be ignored since it represents a removed operand. As
+// consequence, VOIDs must never be used as phi-node operand.
+// This is fine since phi-nodes make no sense with void values
+// but VOID is also used for invalid types and in case of errors.
#include <stdlib.h>
#include <string.h>
--
2.29.2
