[Optimization] Early return for `_apply_matches` and `_iter_placeholders` (#29668)

Signed-off-by: DarkLight1337 <tlleungac@connect.ust.hk>

vllm/multimodal/processing.py

@@ -727,18 +727,35 @@ def _find_matches(
     return mode, matches_to_apply
 
 
+def _all_items_found(
+    mm_item_counts: dict[str, int],
+    mm_found_counts: dict[str, int],
+) -> bool:
+    return all(
+        item_idx >= mm_item_counts[modality]
+        for modality, item_idx in mm_found_counts.items()
+    )
+
+
 def _apply_matches(
     prompt: _S,
     mm_prompt_updates: "MultiModalPromptUpdates",
     tokenizer: AnyTokenizer,
 ) -> tuple[list[_S], "MultiModalPromptUpdatesApplyResult"]:
     prompt_len = len(prompt)
+    mm_item_counts = {m: len(items) for m, items in mm_prompt_updates.items()}
 
     out_seqs = list[str | list[int]]()
     out_result: MultiModalPromptUpdatesApplyResult = {
         m: [None] * len(items) for m, items in mm_prompt_updates.items()
     }
 
+    mm_found_counts = {
+        m: sum(r is not None for r in res) for m, res in out_result.items()
+    }
+    if _all_items_found(mm_item_counts, mm_found_counts):
+        return [prompt], out_result
+
     start_idx = prev_end_idx = 0
     while start_idx < max(prompt_len, 1):  # Allow inserts into empty prompt
         found = False
@@ -776,6 +793,12 @@ def _apply_matches(
                 # Exclude overlapping matches
                 start_idx = prev_end_idx = match.end_idx
 
+            mm_found_counts = {
+                m: sum(r is not None for r in res) for m, res in out_result.items()
+            }
+            if _all_items_found(mm_item_counts, mm_found_counts):
+                break
+
         if not found:
             start_idx += 1
 
@@ -832,12 +855,15 @@ def _iter_placeholders(
 
     Note that empty matches are ignored.
     """
-    prompt_len = len(prompt)
     mm_item_counts = {m: len(items) for m, items in mm_prompt_updates.items()}
+    item_idx_by_modality = {modality: 0 for modality in mm_prompt_updates}
 
-    item_idx_by_modality = defaultdict[str, int](lambda: 0)
+    if _all_items_found(mm_item_counts, item_idx_by_modality):
+        return
 
+    prompt_len = len(prompt)
     start_idx = 0
+
     while start_idx < prompt_len:
         found = False
 
@@ -875,6 +901,9 @@ def _iter_placeholders(
                     break
 
             if found:
+                if _all_items_found(mm_item_counts, item_idx_by_modality):
+                    return
+
                 break  # Go back to the outer while loop
 
         if not found: