Reinstall the patch "Use EmitPointerWithAlignment to get alignment in…

…formation of the pointer used in atomic expr".

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


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@312830 91177308-0d34-0410-b5e6-96231b3b80d8

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) {

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;
+}