From afe3e9586b9040e3a8a0d8e6270f9522bea3c10e Mon Sep 17 00:00:00 2001
From: Stephen Heumann <stephenheumann@gmail.com>
Date: Wed, 12 Jul 2017 23:39:02 -0500
Subject: [PATCH] Fix bad code generation in some cases where compound
 assignment operators are used to update a value through a pointer.

This could occur because a temporary location might be used both in the l-value and r-value computations, but the final assignment code assumed it still had the value from the l-value computation.

The following function demonstrates this problem (*ip is not updated, and *p is trashed):

int badinc(char **p, int *ip)
{
    *ip += *(*p)++;
}
---
 Expression.pas | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/Expression.pas b/Expression.pas
index 0a9fc45..1a11bcf 100644
--- a/Expression.pas
+++ b/Expression.pas
@@ -2967,6 +2967,7 @@ case tree^.token.kind of
          doingScalar := true;
          LoadScalar(id);
          lType := id^.itype;
+         t1 := 0;
          end {if}
       else begin
          doingScalar := false;
@@ -2978,7 +2979,6 @@ case tree^.token.kind of
          Gen2t(pc_str, t1, 0, cgULong);
          Gen2t(pc_lod, t1, 0, cgULong);
          Gen2t(pc_lod, t1, 0, cgULong);
-         FreeTemp(t1, cgLongSize);
          lType := expressionType^.pType;
          if isBitField then begin
             if unsigned then
@@ -3150,6 +3150,8 @@ case tree^.token.kind of
             end; {else}
          Gen0t(pc_bno, lType^.baseType);
          end; {else}
+      if t1 <> 0 then
+         FreeTemp(t1, cgLongSize);
       end; {with}
 
    commach: begin                       {,}