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Reinstall the patch "Use EmitPointerWithAlignment to get alignment information 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

llvm-svn: 312830
This commit is contained in:
Wei Mi 2017-09-08 21:58:18 +00:00
parent bd20f84a63
commit 015a484fe2
2 changed files with 38 additions and 8 deletions
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16
clang/lib/CodeGen/CGAtomic.cpp
View File

@ -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) {

30
clang/test/CodeGenCXX/atomic-align.cpp Normal file
View File

@ -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;
}