[BoundsSafety] Allow evaluating the same CLE in a bounds-check

BoundsSafety can reuse the same CompoundLiteralExpr when emitting a
bounds-check condition. This change allows evaluating the same CLE in
LValueExprEvaluator::VisitCompoundLiteralExpr, and when it was
previously evaluated, we reset the state and evaluate it again.

rdar://157033241

Author: patrykstefanski

clang/lib/AST/ExprConstant.cpp

@@ -9435,6 +9435,20 @@ LValueExprEvaluator::VisitCompoundLiteralExpr(const CompoundLiteralExpr *E) {
     *Lit = APValue();
   } else {
     assert(!Info.getLangOpts().CPlusPlus);
+
+    // TO_UPSTREAM(BoundsSafety) ON
+    // BoundsSafety can reuse the same CLE when emitting a bounds-check
+    // condition. If the state already exist, reset it and evaluate again.
+    // FIXME: Same as above, we could re-use the previously evaluated value.
+    APValue *Val;
+    if (Info.getLangOpts().BoundsSafety &&
+        (Val = Info.CurrentCall->getCurrentTemporary(E))) {
+      Lit = Val;
+      Result.set(E);
+      *Lit = APValue();
+    } else
+    // TO_UPSTREAM(BoundsSafety) OFF
+
     Lit = &Info.CurrentCall->createTemporary(E, E->getInitializer()->getType(),
                                              ScopeKind::Block, Result);
   }

clang/test/BoundsSafety/CodeGen/compound-literal-func-arg-O2.c

@@ -0,0 +1,26 @@
+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --version 5
+
+// RUN: %clang_cc1 -O2 -triple arm64-apple-ios -emit-llvm -fbounds-safety -o - %s | FileCheck %s
+
+void foo(char tag[3]);
+
+// CHECK-LABEL: define void @bar(
+// CHECK-SAME: ) local_unnamed_addr #[[ATTR0:[0-9]+]] {
+// CHECK-NEXT:  [[ENTRY:.*:]]
+// CHECK-NEXT:    [[DOTCOMPOUNDLITERAL:%.*]] = alloca [3 x i8], align 1
+// CHECK-NEXT:    store i8 65, ptr [[DOTCOMPOUNDLITERAL]], align 1, !tbaa [[TBAA2:![0-9]+]]
+// CHECK-NEXT:    [[ARRAYINIT_ELEMENT:%.*]] = getelementptr inbounds nuw i8, ptr [[DOTCOMPOUNDLITERAL]], i64 1
+// CHECK-NEXT:    store i8 66, ptr [[ARRAYINIT_ELEMENT]], align 1, !tbaa [[TBAA2]]
+// CHECK-NEXT:    [[ARRAYINIT_ELEMENT1:%.*]] = getelementptr inbounds nuw i8, ptr [[DOTCOMPOUNDLITERAL]], i64 2
+// CHECK-NEXT:    store i8 67, ptr [[ARRAYINIT_ELEMENT1]], align 1, !tbaa [[TBAA2]]
+// CHECK-NEXT:    call void @foo(ptr noundef nonnull [[DOTCOMPOUNDLITERAL]]) #[[ATTR2:[0-9]+]]
+// CHECK-NEXT:    ret void
+//
+void bar(void) {
+  foo((char[3]){'A', 'B', 'C'});
+}
+//.
+// CHECK: [[TBAA2]] = !{[[META3:![0-9]+]], [[META3]], i64 0}
+// CHECK: [[META3]] = !{!"omnipotent char", [[META4:![0-9]+]], i64 0}
+// CHECK: [[META4]] = !{!"Simple C/C++ TBAA"}
+//.