From 03a9526fe5adae909f1d5fd2736703e69fc46e09 Mon Sep 17 00:00:00 2001
From: Ehud Katz <ehudkatz@gmail.com>
Date: Thu, 16 Apr 2020 13:26:23 +0300
Subject: [PATCH] [CGExprAgg] Fix infinite loop in `findPeephole`

Simplify the function using IgnoreParenNoopCasts.

Fix PR45476

Differential Revision: https://reviews.llvm.org/D78098
---
 clang/lib/CodeGen/CGExprAgg.cpp | 19 ++++++++-----------
 clang/test/CodeGen/pr45476.cpp  | 19 +++++++++++++++++++
 2 files changed, 27 insertions(+), 11 deletions(-)
 create mode 100644 clang/test/CodeGen/pr45476.cpp

diff --git a/clang/lib/CodeGen/CGExprAgg.cpp b/clang/lib/CodeGen/CGExprAgg.cpp
index fa2d228b7eeb..90d4f7e4e096 100644
--- a/clang/lib/CodeGen/CGExprAgg.cpp
+++ b/clang/lib/CodeGen/CGExprAgg.cpp
@@ -677,17 +677,13 @@ AggExprEmitter::VisitCompoundLiteralExpr(CompoundLiteralExpr *E) {
 
 /// Attempt to look through various unimportant expressions to find a
 /// cast of the given kind.
-static Expr *findPeephole(Expr *op, CastKind kind) {
-  while (true) {
-    op = op->IgnoreParens();
-    if (CastExpr *castE = dyn_cast<CastExpr>(op)) {
-      if (castE->getCastKind() == kind)
-        return castE->getSubExpr();
-      if (castE->getCastKind() == CK_NoOp)
-        continue;
-    }
-    return nullptr;
+static Expr *findPeephole(Expr *op, CastKind kind, const ASTContext &ctx) {
+  op = op->IgnoreParenNoopCasts(ctx);
+  if (auto castE = dyn_cast<CastExpr>(op)) {
+    if (castE->getCastKind() == kind)
+      return castE->getSubExpr();
   }
+  return nullptr;
 }
 
 void AggExprEmitter::VisitCastExpr(CastExpr *E) {
@@ -776,7 +772,8 @@ void AggExprEmitter::VisitCastExpr(CastExpr *E) {
       (isToAtomic ? CK_AtomicToNonAtomic : CK_NonAtomicToAtomic);
 
     // These two cases are reverses of each other; try to peephole them.
-    if (Expr *op = findPeephole(E->getSubExpr(), peepholeTarget)) {
+    if (Expr *op =
+            findPeephole(E->getSubExpr(), peepholeTarget, CGF.getContext())) {
       assert(CGF.getContext().hasSameUnqualifiedType(op->getType(),
                                                      E->getType()) &&
            "peephole significantly changed types?");
diff --git a/clang/test/CodeGen/pr45476.cpp b/clang/test/CodeGen/pr45476.cpp
new file mode 100644
index 000000000000..61f3f3649986
--- /dev/null
+++ b/clang/test/CodeGen/pr45476.cpp
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -emit-llvm %s -o - | FileCheck %s
+// PR45476
+
+// This test used to get into an infinite loop,
+// which, in turn, caused clang to never finish execution.
+
+struct s3 {
+  char a, b, c;
+};
+
+_Atomic struct s3 a;
+
+extern "C" void foo() {
+  // CHECK-LABEL: @foo
+  // CHECK: store atomic i32
+
+  a = s3{1, 2, 3};
+}
+