Author: tnorthover
Date: Mon Apr 23 01:16:24 2018
New Revision: 330566
URL: http://llvm.org/viewvc/llvm-project?rev=330566&view=rev
Log:
[Atomics] warn about atomic accesses using libcalls
If an atomic variable is misaligned (and that suspicion is why Clang emits
libcalls at all) the runtime support library will have to use a lock to safely
access it, with potentially very bad performance consequences. There's a very
good chance this is unintentional so it makes sense to issue a warning.
Also give it a named group so people can promote it to an error, or disable it
if they really don't care.
Added:
cfe/trunk/test/CodeGen/atomics-sema-alignment.c
Modified:
cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
cfe/trunk/lib/CodeGen/CGAtomic.cpp
Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=330566&r1=330565&r2=330566&view=diff
==============================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
+++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Mon Apr 23 01:16:24
2018
@@ -7111,6 +7111,9 @@ def warn_atomic_op_has_invalid_memory_or
InGroup<DiagGroup<"atomic-memory-ordering">>;
def err_atomic_op_has_invalid_synch_scope : Error<
"synchronization scope argument to atomic operation is invalid">;
+def warn_atomic_op_misaligned : Warning<
+ "misaligned or large atomic operation may incur significant performance
penalty">,
+ InGroup<DiagGroup<"atomic-alignment">>;
def err_overflow_builtin_must_be_int : Error<
"operand argument to overflow builtin must be an integer (%0 invalid)">;
Modified: cfe/trunk/lib/CodeGen/CGAtomic.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGAtomic.cpp?rev=330566&r1=330565&r2=330566&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CGAtomic.cpp (original)
+++ cfe/trunk/lib/CodeGen/CGAtomic.cpp Mon Apr 23 01:16:24 2018
@@ -18,6 +18,7 @@
#include "TargetInfo.h"
#include "clang/AST/ASTContext.h"
#include "clang/CodeGen/CGFunctionInfo.h"
+#include "clang/Sema/SemaDiagnostic.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Intrinsics.h"
@@ -751,6 +752,13 @@ RValue CodeGenFunction::EmitAtomicExpr(A
Address Dest = Address::invalid();
Address Ptr = EmitPointerWithAlignment(E->getPtr());
+ if (E->getOp() == AtomicExpr::AO__c11_atomic_init ||
+ E->getOp() == AtomicExpr::AO__opencl_atomic_init) {
+ LValue lvalue = MakeAddrLValue(Ptr, AtomicTy);
+ EmitAtomicInit(E->getVal1(), lvalue);
+ return RValue::get(nullptr);
+ }
+
CharUnits sizeChars, alignChars;
std::tie(sizeChars, alignChars) = getContext().getTypeInfoInChars(AtomicTy);
uint64_t Size = sizeChars.getQuantity();
@@ -758,12 +766,8 @@ RValue CodeGenFunction::EmitAtomicExpr(A
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) {
- LValue lvalue = MakeAddrLValue(Ptr, AtomicTy);
- EmitAtomicInit(E->getVal1(), lvalue);
- return RValue::get(nullptr);
- }
+ if (UseLibcall)
+ CGM.getDiags().Report(E->getLocStart(), diag::warn_atomic_op_misaligned);
llvm::Value *Order = EmitScalarExpr(E->getOrder());
llvm::Value *Scope =
Added: cfe/trunk/test/CodeGen/atomics-sema-alignment.c
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/atomics-sema-alignment.c?rev=330566&view=auto
==============================================================================
--- cfe/trunk/test/CodeGen/atomics-sema-alignment.c (added)
+++ cfe/trunk/test/CodeGen/atomics-sema-alignment.c Mon Apr 23 01:16:24 2018
@@ -0,0 +1,27 @@
+// RUN: %clang_cc1 -triple aarch64-linux-gnu %s -emit-llvm -o /dev/null -verify
+
+typedef struct {
+ int a, b;
+} IntPair;
+
+typedef struct {
+ long long a;
+} LongStruct;
+
+typedef int __attribute__((aligned(1))) unaligned_int;
+
+void func(IntPair *p) {
+ IntPair res;
+ __atomic_load(p, &res, 0); // expected-warning {{misaligned or large atomic
operation may incur significant performance penalty}}
+ __atomic_store(p, &res, 0); // expected-warning {{misaligned or large atomic
operation may incur significant performance penalty}}
+ __atomic_fetch_add((unaligned_int *)p, 1, 2); // expected-warning
{{misaligned or large atomic operation may incur significant performance
penalty}}
+ __atomic_fetch_sub((unaligned_int *)p, 1, 3); // expected-warning
{{misaligned or large atomic operation may incur significant performance
penalty}}
+}
+
+void func1(LongStruct *p) {
+ LongStruct res;
+ __atomic_load(p, &res, 0);
+ __atomic_store(p, &res, 0);
+ __atomic_fetch_add((int *)p, 1, 2);
+ __atomic_fetch_sub((int *)p, 1, 3);
+}
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