W22: yield-from pattern-deopt — Alex explicit one-case bypass (C scope)

SonicField · SonicField · commit bffec8965070 · 2026-04-23T07:20:50.000-07:00
Replaces the no-op YIELD_FROM-bytecode removal in d25b2f3 with a correct pattern-deopt for CPython 3.12 'yield from' semantics. CPython 3.12 desugars 'yield from EXPR' into the SEND-loop sequence (GET_YIELD_FROM_ITER, SEND, YIELD_VALUE, RESUME 2, JUMP_BACKWARD_NO_ INTERRUPT, END_SEND). The YIELD_FROM bytecode is a stub in 3.12 (see Python/jit_common/opcode_stubs.h) and never appears in real code, so removing it from isSupportedOpcode was a no-op (caught by testkeeper + medic L3076 epistemic-decay catch). The HIR YieldFrom instruction that triggers W22 is emitted in builder_emit_c.c:hir_builder_emit_yield_value_c when the YIELD_VALUE bytecode is followed by RESUME with oparg==2 (RESUME oparg semantics: 0=function-start, 1=after-plain-yield, 2=after-yield-from, 3=after- await). This commit: 1. Restores 'case YIELD_FROM:' in isSupportedOpcode (the prior d25b2f3 removal was based on incorrect bytecode-existence analysis; the case is dead in 3.12 either way but the misleading comment is removed). 2. Adds pattern-deopt to checkTranslate: when YIELD_VALUE bytecode is followed by RESUME oparg==2, throw runtime_error so the function falls back to the interpreter. This is the EXACT 'yield from' surface — plain yield (RESUME oparg==1) and await (RESUME oparg==3) remain JIT-compiled. dis.dis verification (3 fixtures, /tmp/w22_disdis_fixtures.py): Fixture A yield_from_fn: YIELD_VALUE oparg=2, next=RESUME oparg=2 -> W22 pattern triggers: True (expected) Fixture B plain_yield_fn: YIELD_VALUE oparg=1, next=RESUME oparg=1 -> W22 pattern triggers: False (expected) Fixture C await_fn: YIELD_VALUE oparg=2, next=RESUME oparg=3 -> W22 pattern triggers: False (expected) VERIFICATION: PASS Author authority bypass per Alex L3076 + gatekeeper L3076 + theologian L3076 + supervisor L3076 concur on (C) pattern-deopt scope (narrowest correct option vs (A) deopt-all-yield or (B) deopt-all-SEND). RULE STANDS for future cases — feedback_no_workarounds.md remains in force. Refs: medic L3076 epistemic-decay catch (added discipline lesson: deopt-class commits require dis.dis bytecode-existence verification before commit).
diff --git a/Python/jit/hir/builder.cpp b/Python/jit/hir/builder.cpp
@@ -262,16 +262,9 @@ bool isSupportedOpcode(int opcode) {
     case UNPACK_EX:
     case UNPACK_SEQUENCE:
     case WITH_EXCEPT_START:
+    case YIELD_FROM:
     case YIELD_VALUE:
       return true;
-    // YIELD_FROM deopt: Alex 2026-04-23 W22 explicit one-case bypass of
-    // feedback_no_workarounds.md ('always root-cause, never bail-out/deopt').
-    // Refcount-pass-init n_in==0 generator-resume bug — JIT compilation of
-    // YIELD_FROM hits an inherited CinderX defect (deopt-assertion / immortal
-    // refcount underflow on resume) that 5 architectural fix iterations
-    // could not resolve cleanly. Author authority bypass per Alex L3076 +
-    // gatekeeper L3076. Functions containing YIELD_FROM fall back to the
-    // interpreter (correct, slightly slower). RULE STANDS for future cases.
     default:
       break;
   }
@@ -4934,6 +4927,29 @@ void HIRBuilder::checkTranslate() {
             preloader_.fullname(),
             name_at(oparg))};
       }
+    } else if (opcode == YIELD_VALUE) {
+      // W22 yield-from deopt: Alex 2026-04-23 explicit one-case bypass of
+      // feedback_no_workarounds.md. CPython 3.12 desugars 'yield from EXPR'
+      // into GET_YIELD_FROM_ITER + SEND-loop where the loop body is
+      // (YIELD_VALUE 2, RESUME 2, JUMP_BACKWARD_NO_INTERRUPT). The HIR
+      // YieldFrom instruction is emitted in builder_emit_c.c:hir_builder_emit_
+      // yield_value_c when next bytecode is RESUME with oparg==2 (the
+      // RESUME oparg discriminator: 0=function-start, 1=after-plain-yield,
+      // 2=after-yield-from, 3=after-await). Refcount-pass-init n_in==0 on
+      // the generator-resume bb crashes deopt with 'register not live'
+      // assertion (5 architectural fix iterations did not converge cleanly).
+      // Author authority bypass per Alex L3076 + gatekeeper L3076 + theologian
+      // + supervisor concur on (C) pattern-deopt scope. Plain yield (RESUME
+      // oparg==1) and await (RESUME oparg==3) STAY in the JIT — only the
+      // yield-from desugaring pattern falls back to the interpreter.
+      // RULE STANDS for future cases; this is the ONE explicit exception.
+      auto next_bc = bci.nextInstr();
+      if (next_bc.opcode() == RESUME && next_bc.oparg() == 2) {
+        throw std::runtime_error{fmt::format(
+            "Cannot compile {} to HIR because it uses 'yield from' "
+            "(W22 deopt: YIELD_VALUE+RESUME-oparg-2 pattern)",
+            preloader_.fullname())};
+      }
     }
   }
 }
