[PATCH] D26117: [Devirtualization] Decorate vfunction load with invariant.load

[Piotr Padlewski via cfe-commits]

Prazek created this revision.
Prazek added reviewers: rsmith, rengolin.
Prazek added subscribers: cfe-commits, rjmccall, nlewycky.

This patch was introduced one year ago, but because my google account
was disabled, I didn't get email with failing buildbot and I missed
revert of this commit. There was small but in test regex.
I am back.


https://reviews.llvm.org/D26117

Files:
  lib/CodeGen/ItaniumCXXABI.cpp
  test/CodeGenCXX/virtual-function-calls.cpp


Index: test/CodeGenCXX/virtual-function-calls.cpp
===================================================================
--- test/CodeGenCXX/virtual-function-calls.cpp
+++ test/CodeGenCXX/virtual-function-calls.cpp
@@ -1,4 +1,5 @@
 // RUN: %clang_cc1 %s -triple %itanium_abi_triple -std=c++11 -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 %s -triple %itanium_abi_triple -std=c++11 -emit-llvm -o - -fstrict-vtable-pointers -O1 | FileCheck --check-prefix=CHECK-INVARIANT %s
 
 // PR5021
 namespace PR5021 {
@@ -42,10 +43,14 @@
     [[noreturn]] virtual void f();
   };
 
-  // CHECK: @_ZN15VirtualNoreturn1f
+  // CHECK-LABEL: @_ZN15VirtualNoreturn1f
+  // CHECK-INVARIANT-LABEL: define void @_ZN15VirtualNoreturn1f
   void f(A *p) {
     p->f();
     // CHECK: call {{.*}}void %{{[^#]*$}}
     // CHECK-NOT: unreachable
+    // CHECK-INVARIANT: load {{.*}} !invariant.load ![[EMPTY_NODE:[0-9]+]]
   }
 }
+
+// CHECK-INVARIANT: ![[EMPTY_NODE]] = !{}
Index: lib/CodeGen/ItaniumCXXABI.cpp
===================================================================
--- lib/CodeGen/ItaniumCXXABI.cpp
+++ lib/CodeGen/ItaniumCXXABI.cpp
@@ -1618,7 +1618,16 @@
 
     llvm::Value *VFuncPtr =
         CGF.Builder.CreateConstInBoundsGEP1_64(VTable, VTableIndex, "vfn");
-    return CGF.Builder.CreateAlignedLoad(VFuncPtr, CGF.getPointerAlign());
+    auto *Inst = CGF.Builder.CreateAlignedLoad(VFuncPtr, CGF.getPointerAlign());
+
+    // It's safe to add "invariant.load" without -fstrict-vtable-pointers, but
+    // it would not help in devirtualization.
+    if (CGM.getCodeGenOpts().OptimizationLevel > 0 &&
+        CGM.getCodeGenOpts().StrictVTablePointers)
+      Inst->setMetadata(llvm::LLVMContext::MD_invariant_load,
+                        llvm::MDNode::get(CGM.getLLVMContext(),
+                                          llvm::ArrayRef<llvm::Metadata *>()));
+    return Inst;
   }
 }
 


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