Fix bug causing incorrect code generation in programs that use the 'volatile' keyword.

This bug could both cause accesses to volatile variables to be omitted, and also cause other expressions to be erroneously optimized out in certain circumstances.

As an example, both the access of x and the call to bar() would be erroneously removed in the following program:

#pragma optimize 1
volatile int x;
int bar(void);
void foo(void)
{
    if(x) ;
    if(bar()) ;
}

Note that this patch disables even more optimizations than previously if the 'volatile' keyword is used anywhere in a translation unit. This is necessary for correctness given the current design of ORCA/C, but it means that care should be taken to avoid unnecessary use of 'volatile'.

DAG.pas

@@ -479,13 +479,19 @@ var
       result: boolean;		{temp result}
 
    begin {SideEffects}
-   if (op = nil) or volatile then
-      SideEffects := false
+   if op = nil then begin
+      if volatile then
+         SideEffects := true
+      else
+         SideEffects := false
+      end {if}
    else if op^.opcode in
       [pc_mov,pc_cbf,pc_cop,pc_cpi,pc_cpo,pc_gil,pc_gli,pc_gdl,
        pc_gld,pc_iil,pc_ili,pc_idl,pc_ild,pc_lil,pc_lli,pc_ldl,
        pc_lld,pc_sbf,pc_sro,pc_sto,pc_str,pc_cui,pc_cup,pc_tl1] then
       SideEffects := true
+   else if op^.opcode = pc_ldc then
+      SideEffects := false
    else
       SideEffects := SideEffects(op^.left) or SideEffects(op^.right);
    end; {SideEffects}