Author: rnk
Date: Wed Jan 21 16:18:17 2015
New Revision: 226707
URL: http://llvm.org/viewvc/llvm-project?rev=226707&view=rev
Log:
Add the "thunk" attribute to MS ABI virtual member pointers
This attribute implies indicates that the function musttail calls
another function and returns whatever it returns. The return type of the
thunk is meaningless, as the thunk can dynamically call different
functions with different return types. So long as the callers bitcast
the thunk with the correct type, behavior is well defined.
This attribute was necessary to fix PR20944, where the indirect call
combiner noticed that the thunk returned void and replaced the results
of the indirect call instruction with undef.
Over-the-shoulder reviewed by David Majnemer.
Modified:
cfe/trunk/lib/CodeGen/MicrosoftCXXABI.cpp
cfe/trunk/test/CodeGenCXX/microsoft-abi-virtual-member-pointers.cpp
Modified: cfe/trunk/lib/CodeGen/MicrosoftCXXABI.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/MicrosoftCXXABI.cpp?rev=226707&r1=226706&r2=226707&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/MicrosoftCXXABI.cpp (original)
+++ cfe/trunk/lib/CodeGen/MicrosoftCXXABI.cpp Wed Jan 21 16:18:17 2015
@@ -1540,6 +1540,12 @@ llvm::Function *MicrosoftCXXABI::EmitVir
CGM.SetLLVMFunctionAttributes(MD, FnInfo, ThunkFn);
CGM.SetLLVMFunctionAttributesForDefinition(MD, ThunkFn);
+ // Add the "thunk" attribute so that LLVM knows that the return type is
+ // meaningless. These thunks can be used to call functions with differing
+ // return types, and the caller is required to cast the prototype
+ // appropriately to extract the correct value.
+ ThunkFn->addFnAttr("thunk");
+
// These thunks can be compared, so they are not unnamed.
ThunkFn->setUnnamedAddr(false);
Modified: cfe/trunk/test/CodeGenCXX/microsoft-abi-virtual-member-pointers.cpp
URL:
http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/microsoft-abi-virtual-member-pointers.cpp?rev=226707&r1=226706&r2=226707&view=diff
==============================================================================
--- cfe/trunk/test/CodeGenCXX/microsoft-abi-virtual-member-pointers.cpp
(original)
+++ cfe/trunk/test/CodeGenCXX/microsoft-abi-virtual-member-pointers.cpp Wed Jan
21 16:18:17 2015
@@ -62,6 +62,7 @@ void f() {
// Thunk for calling the 1st virtual function in C with no parameters.
// CHECK32-LABEL: define linkonce_odr x86_thiscallcc void
@"\01??_9C@@$BA@AE"(%struct.C* %this, ...)
+// CHECK32: #[[ATTR:[0-9]+]]
// CHECK32-NOT: unnamed_addr
// CHECK32: comdat
// CHECK32: [[VPTR:%.*]] = getelementptr inbounds void (%struct.C*, ...)**
%{{.*}}, i64 0
@@ -71,6 +72,7 @@ void f() {
// CHECK32: }
//
// CHECK64-LABEL: define linkonce_odr void @"\01??_9C@@$BA@AA"(%struct.C*
%this, ...)
+// CHECK64: #[[ATTR:[0-9]+]]
// CHECK64-NOT: unnamed_addr
// CHECK64: comdat
// CHECK64: [[VPTR:%.*]] = getelementptr inbounds void (%struct.C*, ...)**
%{{.*}}, i64 0
@@ -80,14 +82,16 @@ void f() {
// CHECK64: }
// Thunk for calling the 2nd virtual function in C, taking int and double as
parameters, returning int.
-// CHECK32-LABEL: define linkonce_odr x86_thiscallcc void
@"\01??_9C@@$B3AE"(%struct.C* %this, ...) {{.*}} comdat
+// CHECK32-LABEL: define linkonce_odr x86_thiscallcc void
@"\01??_9C@@$B3AE"(%struct.C* %this, ...)
+// CHECK32: #[[ATTR]] comdat
// CHECK32: [[VPTR:%.*]] = getelementptr inbounds void (%struct.C*, ...)**
%{{.*}}, i64 1
// CHECK32: [[CALLEE:%.*]] = load void (%struct.C*, ...)** [[VPTR]]
// CHECK32: musttail call x86_thiscallcc void (%struct.C*, ...)*
[[CALLEE]](%struct.C* %{{.*}}, ...)
// CHECK32-NEXT: ret void
// CHECK32: }
//
-// CHECK64-LABEL: define linkonce_odr void @"\01??_9C@@$B7AA"(%struct.C*
%this, ...) {{.*}} comdat
+// CHECK64-LABEL: define linkonce_odr void @"\01??_9C@@$B7AA"(%struct.C*
%this, ...)
+// CHECK64: #[[ATTR]] comdat
// CHECK64: [[VPTR:%.*]] = getelementptr inbounds void (%struct.C*, ...)**
%{{.*}}, i64 1
// CHECK64: [[CALLEE:%.*]] = load void (%struct.C*, ...)** [[VPTR]]
// CHECK64: musttail call void (%struct.C*, ...)* [[CALLEE]](%struct.C*
%{{.*}}, ...)
@@ -95,14 +99,16 @@ void f() {
// CHECK64: }
// Thunk for calling the 3rd virtual function in C, taking an int parameter,
returning a struct.
-// CHECK32-LABEL: define linkonce_odr x86_thiscallcc void
@"\01??_9C@@$B7AE"(%struct.C* %this, ...) {{.*}} comdat
+// CHECK32-LABEL: define linkonce_odr x86_thiscallcc void
@"\01??_9C@@$B7AE"(%struct.C* %this, ...)
+// CHECK32: #[[ATTR]] comdat
// CHECK32: [[VPTR:%.*]] = getelementptr inbounds void (%struct.C*, ...)**
%{{.*}}, i64 2
// CHECK32: [[CALLEE:%.*]] = load void (%struct.C*, ...)** [[VPTR]]
// CHECK32: musttail call x86_thiscallcc void (%struct.C*, ...)*
[[CALLEE]](%struct.C* %{{.*}}, ...)
// CHECK32-NEXT: ret void
// CHECK32: }
//
-// CHECK64-LABEL: define linkonce_odr void @"\01??_9C@@$BBA@AA"(%struct.C*
%this, ...) {{.*}} comdat
+// CHECK64-LABEL: define linkonce_odr void @"\01??_9C@@$BBA@AA"(%struct.C*
%this, ...)
+// CHECK64: #[[ATTR]] comdat
// CHECK64: [[VPTR:%.*]] = getelementptr inbounds void (%struct.C*, ...)**
%{{.*}}, i64 2
// CHECK64: [[CALLEE:%.*]] = load void (%struct.C*, ...)** [[VPTR]]
// CHECK64: musttail call void (%struct.C*, ...)* [[CALLEE]](%struct.C*
%{{.*}}, ...)
@@ -111,6 +117,7 @@ void f() {
// Thunk for calling the virtual function in internal class D.
// CHECK32-LABEL: define internal x86_thiscallcc void
@"\01??_9D@?A@@$BA@AE"(%"struct.(anonymous namespace)::D"* %this, ...)
+// CHECK32: #[[ATTR]]
// CHECK32: [[VPTR:%.*]] = getelementptr inbounds void (%"struct.(anonymous
namespace)::D"*, ...)** %{{.*}}, i64 0
// CHECK32: [[CALLEE:%.*]] = load void (%"struct.(anonymous namespace)::D"*,
...)** [[VPTR]]
// CHECK32: musttail call x86_thiscallcc void (%"struct.(anonymous
namespace)::D"*, ...)* [[CALLEE]](%"struct.(anonymous namespace)::D"* %{{.*}},
...)
@@ -118,6 +125,7 @@ void f() {
// CHECK32: }
//
// CHECK64-LABEL: define internal void
@"\01??_9D@?A@@$BA@AA"(%"struct.(anonymous namespace)::D"* %this, ...)
+// CHECK64: #[[ATTR]]
// CHECK64: [[VPTR:%.*]] = getelementptr inbounds void (%"struct.(anonymous
namespace)::D"*, ...)** %{{.*}}, i64 0
// CHECK64: [[CALLEE:%.*]] = load void (%"struct.(anonymous namespace)::D"*,
...)** [[VPTR]]
// CHECK64: musttail call void (%"struct.(anonymous namespace)::D"*, ...)*
[[CALLEE]](%"struct.(anonymous namespace)::D"* %{{.*}}, ...)
@@ -139,3 +147,5 @@ void f() {
// CHECK64: musttail call void (%struct.C*, ...)* [[CALLEE]](%struct.C*
%{{.*}}, ...)
// CHECK64: ret void
// CHECK64: }
+
+// CHECK32: #[[ATTR]] = {{{.*}}"thunk"{{.*}}}
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