[qfcc] Set a flowvar's minimum size based on usage

But really only for memset and memmove because they need to use an int
alias of the variable and it may be only that alias that sets a much
larger variable.

tools/qfcc/include/flow.h

@@ -49,6 +49,7 @@ typedef struct flowvar_s {
 	struct operand_s *op;		///< an operand using this var
 	int         number;			///< number of variable in func's ref list
 	int         flowaddr;		///< psuedo address for local and temp vars
+	int         minsize;		///< minimum size (via memset/move)
 } flowvar_t;
 
 typedef struct udchain_s {

tools/qfcc/source/flow.c

@@ -572,7 +572,11 @@ clear_operand_chain (operand_t *op)
 static void
 add_var_addrs (set_t *set, flowvar_t *var)
 {
-	for (int i = 0; i < var->op->size; i++) {
+	int size = var->op->size;
+	if (size < var->minsize) {
+		size = var->minsize;
+	}
+	for (int i = 0; i < size; i++) {
 		set_add (set, var->flowaddr + i);
 	}
 }
@@ -835,6 +839,17 @@ flow_add_op_var (set_t *set, operand_t *op, int ol)
 	}
 }
 
+static void
+flow_set_minsize (operand_t *op, int size)
+{
+	flowvar_t  *var;
+	if (!(var = flow_get_var (op)))
+		return;
+	if (var->minsize < size) {
+		var->minsize = size;
+	}
+}
+
 static void
 flow_add_op_var_size (set_t *set, operand_t *op, int size, int ol)
 {
@@ -1605,6 +1620,12 @@ flow_analyze_statement (statement_t *s, set_t *use, set_t *def, set_t *kill,
 					print_type (s->opb->type);
 					internal_error (s->expr, "unexpected type for memset/move");
 				}
+				if (s->type == st_move) {
+					flow_set_minsize (s->opa, size);
+				}
+				if (s->type == st_move || s->type == st_memset) {
+					flow_set_minsize (s->opc, size);
+				}
 			} else {
 				size = -1;
 			}