[ObjC][ARC] Fix non-deterministic behavior in ProvenanceAnalysis

If the second value passed to relatedSelect is a select, check whether
neither arm of the select is related to the first value.

llvm/lib/Transforms/ObjCARC/ProvenanceAnalysis.cpp

@@ -42,11 +42,17 @@ bool ProvenanceAnalysis::relatedSelect(const SelectInst *A,
                                        const Value *B) {
   // If the values are Selects with the same condition, we can do a more precise
   // check: just check for relations between the values on corresponding arms.
-  if (const SelectInst *SB = dyn_cast<SelectInst>(B))
+  if (const SelectInst *SB = dyn_cast<SelectInst>(B)) {
     if (A->getCondition() == SB->getCondition())
       return related(A->getTrueValue(), SB->getTrueValue()) ||
              related(A->getFalseValue(), SB->getFalseValue());
 
+    // Check both arms of B individually. Return false if neither arm is related
+    // to A.
+    if (!(related(SB->getTrueValue(), A) || related(SB->getFalseValue(), A)))
+      return false;
+  }
+
   // Check both arms of the Select node individually.
   return related(A->getTrueValue(), B) || related(A->getFalseValue(), B);
 }

llvm/test/Transforms/ObjCARC/related-check.ll

@@ -132,6 +132,19 @@ define ptr @foo() {
   ret ptr %call78
 }
 
+; CHECK-LABEL: define void @test_select(
+; CHECK: call ptr @llvm.objc.retain(
+; CHECK: call void @llvm.objc.release(
+
+define void @test_select(i1 %c0, i1 %c1, ptr %p0, ptr %p1) {
+  %cond = select i1 %c0, ptr %p0, ptr %p1
+  %cond5 = select i1 %c0, ptr %p1, ptr %p0
+  %cond14 = select i1 %c1, ptr %cond5, ptr null
+  call ptr @llvm.objc.retain(ptr %cond14)
+  call void @llvm.objc.release(ptr %cond)
+  ret void
+}
+
 declare ptr @bar(ptr)
 
 declare ptr @llvm.objc.retain(ptr)