[core] Drop noinline from IIFE chunks and rename helper

Additional measurements showed GCC's -Os inliner re-inlines most IIFE
chunks back into setup() by choice, and the structural scoping alone
captures nearly all of the peak-stack benefit on esp32 without the
flash cost of forcing all chunks to stay as real functions.

Apollo (esp32-s3, -Os) with vs without noinline:
  peak setup stack     176 B (noinline)  vs  304 B (scope-only)
  flash delta         +388 B (noinline)  vs   -504 B (scope-only)
  chunks kept          86               vs    20

Issue #15796 is an LVGL-setup class of bug that has only surfaced on
esp32 after years in the field; the extra guarantee that noinline
provides is not worth the flash cost in practice. Also rename the
helper from _wrap_in_noinline_iifes to _wrap_in_iifes to match.

esphome/core/__init__.py

@@ -531,18 +531,19 @@ class Library:
         return self
 
 
-def _wrap_in_noinline_iifes(lines: list[str], max_statements: int) -> list[str]:
-    """Wrap ``lines`` in one or more ``[]() __attribute__((noinline)) {...}();`` IIFEs.
+def _wrap_in_iifes(lines: list[str], max_statements: int) -> list[str]:
+    """Wrap ``lines`` in one or more ``[]() {...}();`` IIFEs.
 
     Splits into IIFEs of up to ``max_statements`` entries each. Never splits
     inside a brace-balanced block (e.g. the ``{`` / ``}`` pair that
     ``cg.with_local_variable()`` emits around a scoped local), so an IIFE
     may exceed ``max_statements`` when a block straddles the boundary.
 
-    GCC note: ``__attribute__((noinline))`` between the lambda parameter
-    list and body binds to ``operator()``. The C++ standard-attribute
-    spelling ``[[gnu::noinline]]`` in that position binds to the return
-    type instead and produces ``-Wattributes`` warnings.
+    The IIFEs intentionally have no ``noinline`` attribute: GCC's ``-Os``
+    inliner makes good decisions about which chunks to keep as functions
+    and which to re-inline, and forcing all chunks to stay as functions
+    costs flash without measurably improving peak stack on configs where
+    the scope structure is itself sufficient to bound live-range lifetimes.
     """
     out: list[str] = []
     chunk: list[str] = []
@@ -551,7 +552,7 @@ def _wrap_in_noinline_iifes(lines: list[str], max_statements: int) -> list[str]:
     def flush() -> None:
         if not chunk:
             return
-        out.append("[]() __attribute__((noinline)) {")
+        out.append("[]() {")
         out.extend(chunk)
         out.append("}();")
         chunk.clear()
@@ -1065,7 +1066,7 @@ class EsphomeCore:
         # (e.g. sensor platforms with many filter registrations).
         pieces = list(prefix)
         for block in components:
-            pieces.extend(_wrap_in_noinline_iifes(block, max_statements=50))
+            pieces.extend(_wrap_in_iifes(block, max_statements=50))
         return "\n".join(pieces) + "\n\n"
 
     @property

tests/unit_tests/test_core.py

@@ -870,14 +870,14 @@ class TestEsphomeCore:
         assert "Wire" in target.platformio_libraries
 
 
-def test_wrap_in_noinline_iifes_empty_input() -> None:
-    assert not core._wrap_in_noinline_iifes([], max_statements=10)
+def test_wrap_in_iifes_empty_input() -> None:
+    assert not core._wrap_in_iifes([], max_statements=10)
 
 
-def test_wrap_in_noinline_iifes_fewer_lines_than_limit() -> None:
+def test_wrap_in_iifes_fewer_lines_than_limit() -> None:
     lines = ["a();", "b();", "c();"]
-    assert core._wrap_in_noinline_iifes(lines, max_statements=10) == [
-        "[]() __attribute__((noinline)) {",
+    assert core._wrap_in_iifes(lines, max_statements=10) == [
+        "[]() {",
         "a();",
         "b();",
         "c();",
@@ -885,51 +885,51 @@ def test_wrap_in_noinline_iifes_fewer_lines_than_limit() -> None:
     ]
 
 
-def test_wrap_in_noinline_iifes_splits_at_max_statements() -> None:
+def test_wrap_in_iifes_splits_at_max_statements() -> None:
     lines = [f"s{i}();" for i in range(5)]
-    result = core._wrap_in_noinline_iifes(lines, max_statements=2)
+    result = core._wrap_in_iifes(lines, max_statements=2)
     # With max=2 and 5 lines: chunks of 2, 2, 1 → 3 IIFEs.
     assert sum(1 for line in result if line.startswith("[]()")) == 3
 
 
-def test_wrap_in_noinline_iifes_never_splits_inside_braces() -> None:
+def test_wrap_in_iifes_never_splits_inside_braces() -> None:
     # max=2 would naively split after "{" but brace guard keeps block whole.
     lines = ["a();", "{", "inner();", "}", "b();"]
-    assert core._wrap_in_noinline_iifes(lines, max_statements=2) == [
-        "[]() __attribute__((noinline)) {",
+    assert core._wrap_in_iifes(lines, max_statements=2) == [
+        "[]() {",
         "a();",
         "{",
         "inner();",
         "}",
         "}();",
-        "[]() __attribute__((noinline)) {",
+        "[]() {",
         "b();",
         "}();",
     ]
 
 
-def test_wrap_in_noinline_iifes_nested_braces() -> None:
+def test_wrap_in_iifes_nested_braces() -> None:
     lines = ["{", "{", "deep();", "}", "}", "after();"]
-    assert core._wrap_in_noinline_iifes(lines, max_statements=1) == [
-        "[]() __attribute__((noinline)) {",
+    assert core._wrap_in_iifes(lines, max_statements=1) == [
+        "[]() {",
         "{",
         "{",
         "deep();",
         "}",
         "}",
         "}();",
-        "[]() __attribute__((noinline)) {",
+        "[]() {",
         "after();",
         "}();",
     ]
 
 
-def test_wrap_in_noinline_iifes_unbalanced_braces_fall_through() -> None:
+def test_wrap_in_iifes_unbalanced_braces_fall_through() -> None:
     # Pathological input where "}" appears before "{": don't crash; emit
     # a single IIFE with all lines rather than splitting mid-flight.
     lines = ["a();", "}", "b();"]
-    result = core._wrap_in_noinline_iifes(lines, max_statements=1)
-    assert result[0] == "[]() __attribute__((noinline)) {"
+    result = core._wrap_in_iifes(lines, max_statements=1)
+    assert result[0] == "[]() {"
     assert result[-1] == "}();"
     assert [line for line in result if line in lines] == lines
 
@@ -952,7 +952,7 @@ def test_cpp_main_section_component_marker_wraps_in_iife() -> None:
         RawStatement("new_wifi();"),
     ]
     out = target.cpp_main_section
-    assert out.count("[]() __attribute__((noinline)) {") == 2
+    assert out.count("[]() {") == 2
     assert out.count("}();") == 2
     assert "// === logger ===" in out
     assert "// === wifi ===" in out
@@ -966,4 +966,4 @@ def test_cpp_main_section_prefix_statements_stay_outside_iife() -> None:
         RawStatement("body();"),
     ]
     out = target.cpp_main_section
-    assert out.index("prefix();") < out.index("[]() __attribute__((noinline)) {")
+    assert out.index("prefix();") < out.index("[]() {")