[CodeGen] Pessimize aliasing for member unions (and may-alias) objects

Use the TBAA info of the omnipotent char for these objects.

Differential Revision: https://reviews.llvm.org/D33328

llvm-svn: 303851

clang/lib/CodeGen/CGExpr.cpp

@@ -1432,11 +1432,12 @@ llvm::Value *CodeGenFunction::EmitLoadOfScalar(Address Addr, bool Volatile,
     Load->setMetadata(CGM.getModule().getMDKindID("nontemporal"), Node);
   }
   if (TBAAInfo) {
-    llvm::MDNode *TBAAPath = CGM.getTBAAStructTagInfo(TBAABaseType, TBAAInfo,
-                                                      TBAAOffset);
-    if (TBAAPath)
-      CGM.DecorateInstructionWithTBAA(Load, TBAAPath,
-                                      false /*ConvertTypeToTag*/);
+    bool MayAlias = BaseInfo.getMayAlias();
+    llvm::MDNode *TBAA = MayAlias
+        ? CGM.getTBAAInfo(getContext().CharTy)
+        : CGM.getTBAAStructTagInfo(TBAABaseType, TBAAInfo, TBAAOffset);
+    if (TBAA)
+      CGM.DecorateInstructionWithTBAA(Load, TBAA, MayAlias);
   }
 
   if (EmitScalarRangeCheck(Load, Ty, Loc)) {
@@ -1522,11 +1523,12 @@ void CodeGenFunction::EmitStoreOfScalar(llvm::Value *Value, Address Addr,
     Store->setMetadata(CGM.getModule().getMDKindID("nontemporal"), Node);
   }
   if (TBAAInfo) {
-    llvm::MDNode *TBAAPath = CGM.getTBAAStructTagInfo(TBAABaseType, TBAAInfo,
-                                                      TBAAOffset);
-    if (TBAAPath)
-      CGM.DecorateInstructionWithTBAA(Store, TBAAPath,
-                                      false /*ConvertTypeToTag*/);
+    bool MayAlias = BaseInfo.getMayAlias();
+    llvm::MDNode *TBAA = MayAlias
+        ? CGM.getTBAAInfo(getContext().CharTy)
+        : CGM.getTBAAStructTagInfo(TBAABaseType, TBAAInfo, TBAAOffset);
+    if (TBAA)
+      CGM.DecorateInstructionWithTBAA(Store, TBAA, MayAlias);
   }
 }
 
@@ -3535,6 +3537,11 @@ LValue CodeGenFunction::EmitLValueForField(LValue base,
     getFieldAlignmentSource(BaseInfo.getAlignmentSource());
   LValueBaseInfo FieldBaseInfo(fieldAlignSource, BaseInfo.getMayAlias());
 
+  const RecordDecl *rec = field->getParent();
+  if (rec->isUnion() || rec->hasAttr<MayAliasAttr>())
+    FieldBaseInfo.setMayAlias(true);
+  bool mayAlias = FieldBaseInfo.getMayAlias();
+
   if (field->isBitField()) {
     const CGRecordLayout &RL =
       CGM.getTypes().getCGRecordLayout(field->getParent());
@@ -3556,11 +3563,7 @@ LValue CodeGenFunction::EmitLValueForField(LValue base,
     return LValue::MakeBitfield(Addr, Info, fieldType, FieldBaseInfo);
   }
 
-  const RecordDecl *rec = field->getParent();
   QualType type = field->getType();
-
-  bool mayAlias = rec->hasAttr<MayAliasAttr>();
-
   Address addr = base.getAddress();
   unsigned cvr = base.getVRQualifiers();
   bool TBAAPath = CGM.getCodeGenOpts().StructPathTBAA;

clang/test/CodeGen/union-tbaa1.c

@@ -0,0 +1,44 @@
+// RUN: %clang_cc1 %s -triple hexagon-unknown-elf -O2 -emit-llvm -o - | FileCheck %s
+
+typedef union __attribute__((aligned(4))) {
+  unsigned short uh[2];
+  unsigned uw;
+} vect32;
+
+void bar(vect32 p[][2]);
+
+// CHECK-LABEL: define void @fred
+void fred(unsigned Num, int Vec[2], int *Index, int Arr[4][2]) {
+  vect32 Tmp[4][2];
+// Generate tbaa for the load of Index:
+// CHECK: load i32, i32* %Index{{.*}}tbaa
+// But no tbaa for the two stores:
+// CHECK: %uw[[UW1:[0-9]*]] = getelementptr
+// CHECK: store{{.*}}%uw[[UW1]]
+// CHECK: tbaa ![[OCPATH:[0-9]+]]
+// There will be a load after the store, and it will use tbaa. Make sure
+// the check-not above doesn't find it:
+// CHECK: load
+  Tmp[*Index][0].uw = Arr[*Index][0] * Num;
+// CHECK: %uw[[UW2:[0-9]*]] = getelementptr
+// CHECK: store{{.*}}%uw[[UW2]]
+// CHECK: tbaa ![[OCPATH]]
+  Tmp[*Index][1].uw = Arr[*Index][1] * Num;
+// Same here, don't generate tbaa for the loads:
+// CHECK: %uh[[UH1:[0-9]*]] = bitcast %union.vect32
+// CHECK: %arrayidx[[AX1:[0-9]*]] = getelementptr{{.*}}%uh[[UH1]]
+// CHECK: load i16, i16* %arrayidx[[AX1]]
+// CHECK: tbaa ![[OCPATH]]
+// CHECK: store
+  Vec[0] = Tmp[*Index][0].uh[1];
+// CHECK: %uh[[UH2:[0-9]*]] = bitcast %union.vect32
+// CHECK: %arrayidx[[AX2:[0-9]*]] = getelementptr{{.*}}%uh[[UH2]]
+// CHECK: load i16, i16* %arrayidx[[AX2]]
+// CHECK: tbaa ![[OCPATH]]
+// CHECK: store
+  Vec[1] = Tmp[*Index][1].uh[1];
+  bar(Tmp);
+}
+
+// CHECK-DAG: ![[CHAR:[0-9]+]] = !{!"omnipotent char"
+// CHECK-DAG: ![[OCPATH]] = !{![[CHAR]], ![[CHAR]], i64 0}

clang/test/CodeGenCXX/union-tbaa2.cpp

@@ -0,0 +1,45 @@
+// RUN: %clang_cc1 %s -O2 -std=c++11 -triple x86_64-unknown-linux-gnu -target-cpu x86-64 -target-feature +sse4.2 -target-feature +avx -emit-llvm -o - | FileCheck %s
+
+// Testcase from llvm.org/PR32056
+
+extern "C" int printf (const char *__restrict __format, ...);
+
+typedef double __m256d __attribute__((__vector_size__(32)));
+
+static __inline __m256d __attribute__((__always_inline__, __nodebug__,
+                                       __target__("avx")))
+_mm256_setr_pd(double __a, double __b, double __c, double __d) {
+  return (__m256d){ __a, __b, __c, __d };
+}
+
+struct A {
+  A () {
+// Check that the TBAA information generated for the stores to the
+// union members is based on the omnipotent char.
+// CHECK: store <4 x double>
+// CHECK: tbaa ![[OCPATH:[0-9]+]]
+// CHECK: store <4 x double>
+// CHECK: tbaa ![[OCPATH]]
+// CHECK: call
+    a = _mm256_setr_pd(0.0, 1.0, 2.0, 3.0);
+    b = _mm256_setr_pd(4.0, 5.0, 6.0, 7.0);
+  }
+
+  const double *begin() { return c; }
+  const double *end() { return c+8; }
+
+  union {
+    struct { __m256d a, b; };
+    double c[8];
+  };
+};
+
+int main(int argc, char *argv[]) {
+  A a;
+  for (double value : a)
+    printf("%f ", value);
+  return 0;
+}
+
+// CHECK-DAG: ![[CHAR:[0-9]+]] = !{!"omnipotent char"
+// CHECK-DAG: ![[OCPATH]] = !{![[CHAR]], ![[CHAR]], i64 0}