Reinstall the patch "Use EmitPointerWithAlignment to get alignment information of the pointer used in atomic expr" after fixing PR31620.

This is to fix PR34347. EmitAtomicExpr now only uses alignment information from
Type, instead of Decl, so when the declaration of an atomic variable is marked
to have the alignment equal as its size, EmitAtomicExpr doesn't know about it and
will generate libcall instead of atomic op. The patch uses EmitPointerWithAlignment
to get the precise alignment information.

Differential Revision: https://reviews.llvm.org/D37310

llvm-svn: 314145

2 files changed, 38 insertions, 8 deletions

diff --git a/clang/lib/CodeGen/CGAtomic.cpp b/clang/lib/CodeGen/CGAtomic.cpp
index d42740c0662..d2aa5683ff7 100644
--- a/clang/lib/CodeGen/CGAtomic.cpp
+++ b/clang/lib/CodeGen/CGAtomic.cpp
@@ -745,19 +745,19 @@ RValue CodeGenFunction::EmitAtomicExpr(AtomicExpr *E) {
   QualType MemTy = AtomicTy;
   if (const AtomicType *AT = AtomicTy->getAs<AtomicType>())
     MemTy = AT->getValueType();
-  CharUnits sizeChars, alignChars;
-  std::tie(sizeChars, alignChars) = getContext().getTypeInfoInChars(AtomicTy);
-  uint64_t Size = sizeChars.getQuantity();
-  unsigned MaxInlineWidthInBits = getTarget().getMaxAtomicInlineWidth();
-  bool UseLibcall = (sizeChars != alignChars ||
-                     getContext().toBits(sizeChars) > MaxInlineWidthInBits);
-
   llvm::Value *IsWeak = nullptr, *OrderFail = nullptr;
 
   Address Val1 = Address::invalid();
   Address Val2 = Address::invalid();
   Address Dest = Address::invalid();
-  Address Ptr(EmitScalarExpr(E->getPtr()), alignChars);
+  Address Ptr = EmitPointerWithAlignment(E->getPtr());
+
+  CharUnits sizeChars, alignChars;
+  std::tie(sizeChars, alignChars) = getContext().getTypeInfoInChars(AtomicTy);
+  uint64_t Size = sizeChars.getQuantity();
+  unsigned MaxInlineWidthInBits = getTarget().getMaxAtomicInlineWidth();
+  bool UseLibcall = ((Ptr.getAlignment() % sizeChars) != 0 ||
+                     getContext().toBits(sizeChars) > MaxInlineWidthInBits);
 
   if (E->getOp() == AtomicExpr::AO__c11_atomic_init ||
       E->getOp() == AtomicExpr::AO__opencl_atomic_init) {
diff --git a/clang/test/CodeGenCXX/atomic-align.cpp b/clang/test/CodeGenCXX/atomic-align.cpp
new file mode 100644
index 00000000000..9852ac38a6c
--- /dev/null
+++ b/clang/test/CodeGenCXX/atomic-align.cpp
@@ -0,0 +1,30 @@
+// RUN: %clang_cc1 %s -std=c++11 -emit-llvm -o - -triple=x86_64-linux-gnu | FileCheck %s
+
+struct AM {
+  int f1, f2;
+};
+alignas(8) AM m;
+AM load1() {
+  AM am;
+  // m is declared to align to 8bytes, so generate load atomic instead
+  // of libcall.
+  // CHECK-LABEL: @_Z5load1v
+  // CHECK: load atomic {{.*}} monotonic
+  __atomic_load(&m, &am, 0);
+  return am;
+}
+
+struct BM {
+  int f1;
+  alignas(8) AM f2;
+};
+BM bm;
+AM load2() {
+  AM am;
+  // BM::f2 is declared to align to 8bytes, so generate load atomic instead
+  // of libcall.
+  // CHECK-LABEL: @_Z5load2v
+  // CHECK: load atomic {{.*}} monotonic
+  __atomic_load(&bm.f2, &am, 0);
+  return am;
+}