Fix warnings: screen.c: redraw_asap(): Various (6): MI.

Problems: Argument with 'nonnull' attribute passed null @ 277.
          http://neovim.org/doc/reports/clang/report-9c3614.html#EndPath

          Result of operation is garbage or undefined @ 281.
          http://neovim.org/doc/reports/clang/report-45efbf.html#EndPath

          Argument with 'nonnull' attribute passed null @ 306.
          http://neovim.org/doc/reports/clang/report-ffb84f.html#EndPath

          Result of operation is garbage or undefined @ 311.
          http://neovim.org/doc/reports/clang/report-d04333.html#EndPath

          Argument with 'nonnull' attribute passed null @ 315.
          http://neovim.org/doc/reports/clang/report-786819.html#EndPath

          Uninitialized argument value @ 328.
          http://neovim.org/doc/reports/clang/report-2a5506.html#EndPath

Diagnostic: Multithreading issues.
Rationale : All reported problems can only occur if accesed globals
            change state while executing function, which could only
            happen in a multithreaded environment.
Resolution: Use local variables.
            Note that this change alters function semantics, as now
            function only depends on global values at entry time.
            This shouldn't be a problem, though, as new semantics should
            be in fact better.

1 files changed, 15 insertions, 12 deletions

diff --git a/src/nvim/screen.c b/src/nvim/screen.c
index ac726f7988..450ea5e3f1 100644
--- a/src/nvim/screen.c
+++ b/src/nvim/screen.c
@@ -244,6 +244,9 @@ int redraw_asap(int type)
   u8char_T    *screenlineUC = NULL;     /* copy from ScreenLinesUC[] */
   u8char_T    *screenlineC[MAX_MCO];    /* copy from ScreenLinesC[][] */
   schar_T     *screenline2 = NULL;      /* copy from ScreenLines2[] */
+  const bool l_enc_utf8 = enc_utf8;
+  const int l_enc_dbcs = enc_dbcs;
+  const long l_p_mco = p_mco;
 
   redraw_later(type);
   if (msg_scrolled || (State != NORMAL && State != NORMAL_BUSY))
@@ -254,14 +257,14 @@ int redraw_asap(int type)
   screenline = xmalloc((size_t)(rows * Columns * sizeof(schar_T)));
   screenattr = xmalloc((size_t)(rows * Columns * sizeof(sattr_T)));
 
-  if (enc_utf8) {
+  if (l_enc_utf8) {
     screenlineUC = xmalloc((size_t)(rows * Columns * sizeof(u8char_T)));
 
-    for (i = 0; i < p_mco; ++i) {
+    for (i = 0; i < l_p_mco; ++i) {
       screenlineC[i] = xmalloc((size_t)(rows * Columns * sizeof(u8char_T)));
     }
   }
-  if (enc_dbcs == DBCS_JPNU) {
+  if (l_enc_dbcs == DBCS_JPNU) {
     screenline2 = xmalloc((size_t)(rows * Columns * sizeof(schar_T)));
   }
 
@@ -273,16 +276,16 @@ int redraw_asap(int type)
     memmove(screenattr + r * Columns,
         ScreenAttrs + LineOffset[cmdline_row + r],
         (size_t)Columns * sizeof(sattr_T));
-    if (enc_utf8) {
+    if (l_enc_utf8) {
       memmove(screenlineUC + r * Columns,
           ScreenLinesUC + LineOffset[cmdline_row + r],
           (size_t)Columns * sizeof(u8char_T));
-      for (i = 0; i < p_mco; ++i)
+      for (i = 0; i < l_p_mco; ++i)
         memmove(screenlineC[i] + r * Columns,
             ScreenLinesC[r] + LineOffset[cmdline_row + r],
             (size_t)Columns * sizeof(u8char_T));
     }
-    if (enc_dbcs == DBCS_JPNU)
+    if (l_enc_dbcs == DBCS_JPNU)
       memmove(screenline2 + r * Columns,
           ScreenLines2 + LineOffset[cmdline_row + r],
           (size_t)Columns * sizeof(schar_T));
@@ -302,16 +305,16 @@ int redraw_asap(int type)
       memmove(ScreenAttrs + off,
           screenattr + r * Columns,
           (size_t)Columns * sizeof(sattr_T));
-      if (enc_utf8) {
+      if (l_enc_utf8) {
         memmove(ScreenLinesUC + off,
             screenlineUC + r * Columns,
             (size_t)Columns * sizeof(u8char_T));
-        for (i = 0; i < p_mco; ++i)
+        for (i = 0; i < l_p_mco; ++i)
           memmove(ScreenLinesC[i] + off,
               screenlineC[i] + r * Columns,
               (size_t)Columns * sizeof(u8char_T));
       }
-      if (enc_dbcs == DBCS_JPNU)
+      if (l_enc_dbcs == DBCS_JPNU)
         memmove(ScreenLines2 + off,
             screenline2 + r * Columns,
             (size_t)Columns * sizeof(schar_T));
@@ -322,12 +325,12 @@ int redraw_asap(int type)
 
   free(screenline);
   free(screenattr);
-  if (enc_utf8) {
+  if (l_enc_utf8) {
     free(screenlineUC);
-    for (i = 0; i < p_mco; ++i)
+    for (i = 0; i < l_p_mco; ++i)
       free(screenlineC[i]);
   }
-  if (enc_dbcs == DBCS_JPNU)
+  if (l_enc_dbcs == DBCS_JPNU)
     free(screenline2);
 
   /* Show the intro message when appropriate. */