Merge pull request #77610 from eeckstein/fix-array-element-propagation

ArrayElementValuePropagation: require that the initialization and element-get are in the same block for non-trivial values.

Author: eeckstein

lib/SILOptimizer/Transforms/ArrayElementValuePropagation.cpp

@@ -244,6 +244,17 @@ bool ArrayAllocation::replaceGetElements() {
     if (EltValueIt == ElementValueMap.end())
       continue;
 
+    SILValue element = EltValueIt->second;
+
+    // In OSSA we only insert a copy_value of the element at the array initialization
+    // point. This would result in an over-consume if the getElement is in a loop.
+    // Therefore require that both semantic calls are in the same block.
+    if (ArrayValue->getFunction()->hasOwnership() &&
+        !element->getType().isTrivial(ArrayValue->getFunction()) &&
+        ArrayValue->getParentBlock() != GetElementCall->getParent()) {
+      continue;
+    }
+
     Changed |= GetElement.replaceByValue(EltValueIt->second);
   }
   return Changed;

test/SILOptimizer/array_element_propagation_crash.swift

@@ -15,7 +15,24 @@ func testit(_ arr: inout [Int]) {
 var a = [27]
 testit(&a)
 
+// Second test case:
+var gg = ""
+
+@inline(never)
+func use(_ s: String) {
+  gg = s
+}
+
+func testLoop() {
+  let a = [""]
+
+  for _ in 0..<1000 {
+    use(a[0])
+  }
+}
+
 // As a bonus, also check if the code works as expected.
 // CHECK: [27, 28]
 print(a)
 
+testLoop()