Try to fix portability issue in enum renumbering (again).

The hack embodied in commit 4ba61a487 no longer works after today's change
to allow DatumGetFloat4/Float4GetDatum to be inlined (commit 14cca1bf8).
Probably what's happening is that the faulty compilers are deciding that
the now-inlined assignment is a no-op and so they're not required to
round to float4 width.

We had a bunch of similar issues earlier this year in the degree-based
trig functions, and eventually settled on using volatile intermediate
variables as the least ugly method of forcing recalcitrant compilers
to do what the C standard says (cf commit 82311bcdd).  Let's see if
that method works here.

Discussion: <4640.1472664476@sss.pgh.pa.us>

diff --git a/src/backend/catalog/pg_enum.c b/src/backend/catalog/pg_enum.c
index af89daa7128ee6274b669bc118a7d0bafa6c3d8a..c66f9632c29a3c36843d03df25a0059145a6841c 100644 (file)
--- a/src/backend/catalog/pg_enum.c
+++ b/src/backend/catalog/pg_enum.c
@@ -315,21 +315,21 @@ restart:
            newelemorder = nbr_en->enumsortorder + 1;
        else
        {
-           other_nbr_en = (Form_pg_enum) GETSTRUCT(existing[other_nbr_index]);
-           newelemorder = (nbr_en->enumsortorder +
-                           other_nbr_en->enumsortorder) / 2;
-
            /*
-            * On some machines, newelemorder may be in a register that's
-            * wider than float4.  We need to force it to be rounded to float4
-            * precision before making the following comparisons, or we'll get
-            * wrong results.  (Such behavior violates the C standard, but
-            * fixing the compilers is out of our reach.)
+            * The midpoint value computed here has to be rounded to float4
+            * precision, else our equality comparisons against the adjacent
+            * values are meaningless.  The most portable way of forcing that
+            * to happen with non-C-standard-compliant compilers is to store
+            * it into a volatile variable.
             */
-           newelemorder = DatumGetFloat4(Float4GetDatum(newelemorder));
+           volatile float4 midpoint;
 
-           if (newelemorder == nbr_en->enumsortorder ||
-               newelemorder == other_nbr_en->enumsortorder)
+           other_nbr_en = (Form_pg_enum) GETSTRUCT(existing[other_nbr_index]);
+           midpoint = (nbr_en->enumsortorder +
+                       other_nbr_en->enumsortorder) / 2;
+
+           if (midpoint == nbr_en->enumsortorder ||
+               midpoint == other_nbr_en->enumsortorder)
            {
                RenumberEnumType(pg_enum, existing, nelems);
                /* Clean up and start over */
@@ -337,6 +337,8 @@ restart:
                ReleaseCatCacheList(list);
                goto restart;
            }
+
+           newelemorder = midpoint;
        }
    }