verbose logging for what prevents an inlining from happening

gistfile1.txt

diff --git a/src/spesh/inline.c b/src/spesh/inline.c
index cc58d2d..8c26bfc 100644
--- a/src/spesh/inline.c
+++ b/src/spesh/inline.c
@@ -46,6 +46,8 @@ MVMSpeshGraph * MVM_spesh_inline_try_get_graph(MVMThreadContext *tc, MVMSpeshGra
                                                MVMCode *target, MVMSpeshCandidate *cand) {
     MVMSpeshGraph *ig;
     MVMSpeshBB    *bb;
+    char *frame1_name;
+    char *frame2_name;
 
     /* Check inlining is enabled. */
     if (!tc->instance->spesh_inline_enabled)
@@ -66,6 +68,9 @@ MVMSpeshGraph * MVM_spesh_inline_try_get_graph(MVMThreadContext *tc, MVMSpeshGra
     /* Build graph from the already-specialized bytecode. */
     ig = MVM_spesh_graph_create_from_cand(tc, target->body.sf, cand, 0);
 
+    frame1_name = MVM_string_utf8_encode_C_string(tc, ig->sf->body.name);
+    frame2_name = MVM_string_utf8_encode_C_string(tc, target->body.sf->body.name);
+
     /* Traverse graph, looking for anything that might prevent inlining and
      * also building usage counts up. */
     bb = ig->entry;
@@ -86,17 +91,23 @@ MVMSpeshGraph * MVM_spesh_inline_try_get_graph(MVMThreadContext *tc, MVMSpeshGra
 
             /* Instruction may be marked directly as not being inlinable, in
              * which case we're done. */
-            if (!is_phi && ins->info->no_inline)
+            if (!is_phi && ins->info->no_inline) {
+                fprintf(stderr, "%s prevented an inlining of %s into %s\n", ins->info->name, frame1_name, frame2_name);
                 goto not_inlinable;
+            }
 
             /* If we have lexical access, make sure it's within the frame. */
             if (ins->info->opcode == MVM_OP_getlex) {
-                if (ins->operands[1].lex.outers > 0)
+                if (ins->operands[1].lex.outers > 0) {
+                    fprintf(stderr, "an outer lexical for getlex prevented an inlining of %s into %s\n", ins->info->name, frame1_name, frame2_name);
                     goto not_inlinable;
+                }
             }
             else if (ins->info->opcode == MVM_OP_bindlex) {
-                if (ins->operands[0].lex.outers > 0)
+                if (ins->operands[0].lex.outers > 0) {
+                    fprintf(stderr, "an outer lexical for bindlex prevented an inlining of %s into %s\n", ins->info->name, frame1_name, frame2_name);
                     goto not_inlinable;
+                }
             }
 
             /* Check we don't have too many args for inlining to work out. */
@@ -104,8 +115,10 @@ MVMSpeshGraph * MVM_spesh_inline_try_get_graph(MVMThreadContext *tc, MVMSpeshGra
                     ins->info->opcode == MVM_OP_sp_getarg_i ||
                     ins->info->opcode == MVM_OP_sp_getarg_n ||
                     ins->info->opcode == MVM_OP_sp_getarg_s) {
-                if (ins->operands[1].lit_i16 >= MAX_ARGS_FOR_OPT)
+                if (ins->operands[1].lit_i16 >= MAX_ARGS_FOR_OPT) {
+                    fprintf(stderr, "having too many args prevented an inlining of %s into %s\n", ins->info->name, frame1_name, frame2_name);
                     goto not_inlinable;
+                }
             }
 
             /* Ext-ops need special care in inter-comp-unit inlines. */
@@ -121,11 +134,17 @@ MVMSpeshGraph * MVM_spesh_inline_try_get_graph(MVMThreadContext *tc, MVMSpeshGra
         bb = bb->linear_next;
     }
 
+    MVM_free(frame1_name);
+    MVM_free(frame2_name);
+
     /* If we found nothing we can't inline, inlining is fine. */
     return ig;
 
     /* If we can't find a way to inline, we end up here. */
   not_inlinable:
+    MVM_free(frame1_name);
+    MVM_free(frame2_name);
+
     MVM_spesh_graph_destroy(tc, ig);
     return NULL;
 }