JIT: Avoid VN-based removal of dead byref store in async funcs (#116136)

jakobbotsch · web-flow · commit bf80e0e90b62 · 2025-06-03T12:37:07.000+02:00
diff --git a/src/coreclr/jit/optimizer.cpp b/src/coreclr/jit/optimizer.cpp
@@ -5851,6 +5851,14 @@ PhaseStatus Compiler::optVNBasedDeadStoreRemoval()
             continue;
         }
 
+        if (compIsAsync() && ((varDsc->TypeGet() == TYP_BYREF) ||
+                              ((varDsc->TypeGet() == TYP_STRUCT) && varDsc->GetLayout()->HasGCByRef())))
+        {
+            // A dead store to a byref local may not actually be dead if it
+            // crosses a suspension point.
+            continue;
+        }
+
         for (unsigned defIndex = 1; defIndex < defCount; defIndex++)
         {
             LclSsaVarDsc*        defDsc = varDsc->lvPerSsaData.GetSsaDefByIndex(defIndex);

Original file line number	Diff line number	Diff line change
`@@ -5851,6 +5851,14 @@ PhaseStatus Compiler::optVNBasedDeadStoreRemoval()`
`5851`	`5851`	`continue;`
`5852`	`5852`	`}`
`5853`	`5853`
	`5854`	`+ if (compIsAsync() && ((varDsc->TypeGet() == TYP_BYREF) \|\|`
	`5855`	`+ ((varDsc->TypeGet() == TYP_STRUCT) && varDsc->GetLayout()->HasGCByRef())))`
	`5856`	`+ {`
	`5857`	`+ // A dead store to a byref local may not actually be dead if it`
	`5858`	`+ // crosses a suspension point.`
	`5859`	`+ continue;`
	`5860`	`+ }`
	`5861`	`+`
`5854`	`5862`	`for (unsigned defIndex = 1; defIndex < defCount; defIndex++)`
`5855`	`5863`	`{`
`5856`	`5864`	`LclSsaVarDsc* defDsc = varDsc->lvPerSsaData.GetSsaDefByIndex(defIndex);`