[PATCH] D37310: [Atomic] Merge alignment information from Decl and from Type when emit atomic expression.

[Wei Mi via Phabricator via cfe-commits]

wmi created this revision.
Herald added a subscriber: sanjoy.

This is to fix PR34347.

EmitAtomicExpr will only use 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 don't know about it and will generate libcall 
instead of atomic op.

The patch merge the alignment information from Decl and from Type.


Repository:
  rL LLVM

https://reviews.llvm.org/D37310

Files:
  lib/CodeGen/CGAtomic.cpp
  test/CodeGenCXX/atomic-align.cpp


Index: test/CodeGenCXX/atomic-align.cpp
===================================================================
--- test/CodeGenCXX/atomic-align.cpp
+++ 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;
+}
Index: lib/CodeGen/CGAtomic.cpp
===================================================================
--- lib/CodeGen/CGAtomic.cpp
+++ lib/CodeGen/CGAtomic.cpp
@@ -665,6 +665,20 @@
     MemTy = AT->getValueType();
   CharUnits sizeChars, alignChars;
   std::tie(sizeChars, alignChars) = getContext().getTypeInfoInChars(AtomicTy);
+
+  // Get alignment from declaration.
+  if (const auto *UO = dyn_cast<UnaryOperator>(E->getPtr()))
+    if (UO->getOpcode() == UO_AddrOf) {
+      CharUnits alignDecl;
+      if (const auto *DRE = dyn_cast<DeclRefExpr>(UO->getSubExpr()))
+        alignDecl =
+            
getContext().toCharUnitsFromBits(DRE->getDecl()->getMaxAlignment());
+      else if (const auto *ME = dyn_cast<MemberExpr>(UO->getSubExpr()))
+        alignDecl = getContext().toCharUnitsFromBits(
+            ME->getMemberDecl()->getMaxAlignment());
+      alignChars = std::max(alignChars, alignDecl);
+    }
+
   uint64_t Size = sizeChars.getQuantity();
   unsigned MaxInlineWidthInBits = getTarget().getMaxAtomicInlineWidth();
   bool UseLibcall = (sizeChars != alignChars ||



Index: test/CodeGenCXX/atomic-align.cpp
===================================================================
--- test/CodeGenCXX/atomic-align.cpp
+++ 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;
+}
Index: lib/CodeGen/CGAtomic.cpp
===================================================================
--- lib/CodeGen/CGAtomic.cpp
+++ lib/CodeGen/CGAtomic.cpp
@@ -665,6 +665,20 @@
     MemTy = AT->getValueType();
   CharUnits sizeChars, alignChars;
   std::tie(sizeChars, alignChars) = getContext().getTypeInfoInChars(AtomicTy);
+
+  // Get alignment from declaration.
+  if (const auto *UO = dyn_cast<UnaryOperator>(E->getPtr()))
+    if (UO->getOpcode() == UO_AddrOf) {
+      CharUnits alignDecl;
+      if (const auto *DRE = dyn_cast<DeclRefExpr>(UO->getSubExpr()))
+        alignDecl =
+            getContext().toCharUnitsFromBits(DRE->getDecl()->getMaxAlignment());
+      else if (const auto *ME = dyn_cast<MemberExpr>(UO->getSubExpr()))
+        alignDecl = getContext().toCharUnitsFromBits(
+            ME->getMemberDecl()->getMaxAlignment());
+      alignChars = std::max(alignChars, alignDecl);
+    }
+
   uint64_t Size = sizeChars.getQuantity();
   unsigned MaxInlineWidthInBits = getTarget().getMaxAtomicInlineWidth();
   bool UseLibcall = (sizeChars != alignChars ||

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