[PATCH] D32378: Insert invariant.group.barrier for pointers comparsons

[Piotr Padlewski via Phabricator via cfe-commits]

Prazek created this revision.

This code was wrongly devirtualized before:

  A* a = new A;
  a->foo();
  A* b = new(a) B;
  
  if (a == b)
    b->foo();

Now we insert barrier before comparing dynamic pointers.


https://reviews.llvm.org/D32378

Files:
  lib/CodeGen/CGExprScalar.cpp
  test/CodeGenCXX/strict-vtable-pointers.cpp


Index: test/CodeGenCXX/strict-vtable-pointers.cpp
===================================================================
--- test/CodeGenCXX/strict-vtable-pointers.cpp
+++ test/CodeGenCXX/strict-vtable-pointers.cpp
@@ -237,6 +237,62 @@
   take(u.h);
 }
 
+// CHECK-NEW-LABEL: define void @_Z7comparev()
+void compare() {
+  A *a = new A;
+  a->foo();
+  // CHECK-NEW: call i8* @llvm.invariant.group.barrier(i8*
+  A *b = new (a) B;
+
+  // CHECK-NEW: %[[a:.*]] = call i8* @llvm.invariant.group.barrier(i8*
+  // CHECK-NEW: %[[a2:.*]] = bitcast i8* %[[a]] to %struct.A*
+  // CHECK-NEW: %[[b:.*]] = call i8* @llvm.invariant.group.barrier(i8*
+  // CHECK-NEW: %[[b2:.*]] = bitcast i8* %[[b]] to %struct.A*
+  // CHECK-NEW: %cmp = icmp eq %struct.A* %[[a2]], %[[b2]]
+  if (a == b)
+    b->foo();
+}
+
+// CHECK-NEW-LABEL: compare2
+bool compare2(A *a, A *a2) {
+  // CHECK-NEW: %[[a:.*]] = call i8* @llvm.invariant.group.barrier(i8*
+  // CHECK-NEW: %[[a2:.*]] = bitcast i8* %[[a]] to %struct.A*
+  // CHECK-NEW: %[[b:.*]] = call i8* @llvm.invariant.group.barrier(i8*
+  // CHECK-NEW: %[[b2:.*]] = bitcast i8* %[[b]] to %struct.A*
+  // CHECK-NEW: %cmp = icmp ult %struct.A* %[[a2]], %[[b2]]
+  return a < a2;
+}
+// CHECK-NEW-LABEL: compareIntPointers
+bool compareIntPointers(int *a, int *b) {
+  // CHECK-NEW-NOT: call i8* @llvm.invariant.group.barrier
+  return a == b;
+}
+
+struct HoldingOtherVirtuals {
+  B b;
+};
+
+// There is no need to add barriers for comparision of pointer to classes
+// that are not dynamic.
+// CHECK-NEW-LABEL: compare5
+bool compare5(HoldingOtherVirtuals *a, HoldingOtherVirtuals *b) {
+  // CHECK-NEW-NOT: call i8* @llvm.invariant.group.barrier
+  return a == b;
+}
+
+struct X;
+// We have to also introduce the barriers if comparing pointers to incomplete
+// objects
+// CHECK-NEW-LABEL: define zeroext i1 @_Z8compare4P1XS0_
+bool compare4(X *x, X *x2) {
+  // CHECK-NEW: %[[x:.*]] = call i8* @llvm.invariant.group.barrier(i8*
+  // CHECK-NEW: %[[xp:.*]] = bitcast i8* %[[x]] to %struct.X*
+  // CHECK-NEW: %[[x2:.*]] = call i8* @llvm.invariant.group.barrier(i8*
+  // CHECK-NEW: %[[x2p:.*]] = bitcast i8* %[[x2]] to %struct.X*
+  // CHECK-NEW: %cmp = icmp eq %struct.X* %[[xp]], %[[x2p]]
+  return x == x2;
+}
+
 /** DTORS **/
 // CHECK-DTORS-LABEL: define linkonce_odr void @_ZN10StaticBaseD2Ev(
 // CHECK-DTORS-NOT: call i8* @llvm.invariant.group.barrier(
Index: lib/CodeGen/CGExprScalar.cpp
===================================================================
--- lib/CodeGen/CGExprScalar.cpp
+++ lib/CodeGen/CGExprScalar.cpp
@@ -1698,7 +1698,7 @@
   }
 
   case CK_IntToOCLSampler:
-    return CGF.CGM.createOpenCLIntToSamplerConversion(E, CGF);
+    return CGF.CGM.createOpenCLIntToSamplerConversion(E, CGF);
 
   } // end of switch
 
@@ -3062,8 +3062,20 @@
       Result = Builder.CreateFCmp(FCmpOpc, LHS, RHS, "cmp");
     } else if (LHSTy->hasSignedIntegerRepresentation()) {
       Result = Builder.CreateICmp(SICmpOpc, LHS, RHS, "cmp");
-    } else {
-      // Unsigned integers and pointers.
+    } else { // Unsigned integers and pointers.
+      if (CGF.CGM.getCodeGenOpts().StrictVTablePointers &&
+          CGF.CGM.getCodeGenOpts().OptimizationLevel > 0) {
+        // Based on comparisons of pointers to dynamic objects, the optimizer
+        // can replace one pointer with another. This might result in
+        // replacing pointer after barrier to pointer before barrier,
+        // resulting in invalid devirtualization.
+        if (auto *RD = LHSTy->getPointeeCXXRecordDecl())
+          if (!RD->isCompleteDefinition() || RD->isDynamicClass())
+            LHS = Builder.CreateInvariantGroupBarrier(LHS);
+        if (auto *RD = RHSTy->getPointeeCXXRecordDecl())
+          if (!RD->isCompleteDefinition() || RD->isDynamicClass())
+            RHS = Builder.CreateInvariantGroupBarrier(RHS);
+      }
       Result = Builder.CreateICmp(UICmpOpc, LHS, RHS, "cmp");
     }
 

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