Make FastPathMeta self-contained by copying FmgrInfo structs

FastPathMeta stored pointers into ri_compare_cache entries via
compare_entries[], creating a dependency on that cache remaining
stable.  If ri_compare_cache entries were invalidated after fpmeta
was populated, the pointers would dangle.

Replace compare_entries[] with inline copies of the two FmgrInfo
fields actually needed (cast_func_finfo and eq_opr_finfo), copied
at populate time via fmgr_info_copy().  fpmeta now depends only on
riinfo remaining valid, which is already handled by the invalidation
callback.

Introduced by commit 2da86c1ef9 ("Add fast path for foreign key
constraint checks"), noticed while reviewing code for robustness
under CLOBBER_CACHE_ALWAYS.

Discussion: https://postgr.es/m/CA+HiwqFQ+ZA7hSOygv4uv_t75B3r0_gosjadetCsAEoaZwTu6g@mail.gmail.com

diff --git a/src/backend/utils/adt/ri_triggers.c b/src/backend/utils/adt/ri_triggers.c
index 52bb2f2fee9cd82586adc6c9bdc11e996f8b9662..2de08da6539a5efc3d113745779cb79e122f3fcd 100644 (file)
--- a/src/backend/utils/adt/ri_triggers.c
+++ b/src/backend/utils/adt/ri_triggers.c
@@ -150,7 +150,8 @@ typedef struct RI_CompareHashEntry RI_CompareHashEntry;
 /* Fast-path metadata for RI checks on foreign key referencing tables */
 typedef struct FastPathMeta
 {
-       RI_CompareHashEntry *compare_entries[RI_MAX_NUMKEYS];
+       FmgrInfo        eq_opr_finfo[RI_MAX_NUMKEYS];
+       FmgrInfo        cast_func_finfo[RI_MAX_NUMKEYS];
        RegProcedure regops[RI_MAX_NUMKEYS];
        Oid                     subtypes[RI_MAX_NUMKEYS];
        int                     strats[RI_MAX_NUMKEYS];
@@ -2996,16 +2997,12 @@ build_index_scankeys(const RI_ConstraintInfo *riinfo,
         */
        for (int i = 0; i < riinfo->nkeys; i++)
        {
-               if (pk_nulls[i] != 'n')
-               {
-                       RI_CompareHashEntry *entry = fpmeta->compare_entries[i];
-
-                       if (OidIsValid(entry->cast_func_finfo.fn_oid))
-                               pk_vals[i] = FunctionCall3(&entry->cast_func_finfo,
-                                                                                  pk_vals[i],
-                                                                                  Int32GetDatum(-1),   /* typmod */
-                                                                                  BoolGetDatum(false));        /* implicit coercion */
-               }
+               if (pk_nulls[i] != 'n' &&
+                       OidIsValid(fpmeta->cast_func_finfo[i].fn_oid))
+                       pk_vals[i] = FunctionCall3(&fpmeta->cast_func_finfo[i],
+                                                                          pk_vals[i],
+                                                                          Int32GetDatum(-1),   /* typmod */
+                                                                          BoolGetDatum(false));        /* implicit coercion */
        }
 
        /*
@@ -3048,7 +3045,10 @@ ri_populate_fastpath_metadata(RI_ConstraintInfo *riinfo,
                Oid                     lefttype;
                RI_CompareHashEntry *entry = ri_HashCompareOp(eq_opr, typeid);
 
-               fpmeta->compare_entries[i] = entry;
+               fmgr_info_copy(&fpmeta->cast_func_finfo[i], &entry->cast_func_finfo,
+                                          CurrentMemoryContext);
+               fmgr_info_copy(&fpmeta->eq_opr_finfo[i], &entry->eq_opr_finfo,
+                                          CurrentMemoryContext);
                fpmeta->regops[i] = get_opcode(eq_opr);
 
                get_op_opfamily_properties(eq_opr,