[PATCH] D51416: [RTTI] Align rtti type string to prevent over-alignment

[Dave Green via Phabricator via cfe-commits]

dmgreen created this revision.
dmgreen added reviewers: efriedma, echristo, hfinkel, davide.

Previously the alignment on the newly created rtti string was not set,
meaning that DataLayout::getPreferredAlignment was free to overalign
it to 16 bytes. This causes unnecessary code bloat.


https://reviews.llvm.org/D51416

Files:
  lib/CodeGen/ItaniumCXXABI.cpp
  test/CodeGenCXX/vtable-align.cpp
  test/CodeGenCXX/vtable-linkage.cpp


Index: test/CodeGenCXX/vtable-linkage.cpp
===================================================================
--- test/CodeGenCXX/vtable-linkage.cpp
+++ test/CodeGenCXX/vtable-linkage.cpp
@@ -99,7 +99,7 @@
 // C has no key function, so its vtable should have weak_odr linkage
 // and hidden visibility (rdar://problem/7523229).
 // CHECK-DAG: @_ZTV1C = linkonce_odr unnamed_addr constant {{.*}}, comdat,
-// CHECK-DAG: @_ZTS1C = linkonce_odr constant {{.*}}, comdat{{$}}
+// CHECK-DAG: @_ZTS1C = linkonce_odr constant {{.*}}, comdat, align 1{{$}}
 // CHECK-DAG: @_ZTI1C = linkonce_odr constant {{.*}}, comdat{{$}}
 // CHECK-DAG: @_ZTT1C = linkonce_odr unnamed_addr constant {{.*}}, comdat{{$}}
 
@@ -120,26 +120,26 @@
 // defined in this translation unit, so its vtable should have
 // weak_odr linkage.
 // CHECK-DAG: @_ZTV1EIsE = weak_odr unnamed_addr constant {{.*}}, comdat,
-// CHECK-DAG: @_ZTS1EIsE = weak_odr constant {{.*}}, comdat{{$}}
+// CHECK-DAG: @_ZTS1EIsE = weak_odr constant {{.*}}, comdat, align 1{{$}}
 // CHECK-DAG: @_ZTI1EIsE = weak_odr constant {{.*}}, comdat{{$}}
 
 // F<short> is an explicit template instantiation without a key
 // function, so its vtable should have weak_odr linkage
 // CHECK-DAG: @_ZTV1FIsE = weak_odr unnamed_addr constant {{.*}}, comdat,
-// CHECK-DAG: @_ZTS1FIsE = weak_odr constant {{.*}}, comdat{{$}}
+// CHECK-DAG: @_ZTS1FIsE = weak_odr constant {{.*}}, comdat, align 1{{$}}
 // CHECK-DAG: @_ZTI1FIsE = weak_odr constant {{.*}}, comdat{{$}}
 
 // E<long> is an implicit template instantiation with a key function
 // defined in this translation unit, so its vtable should have
 // linkonce_odr linkage.
 // CHECK-DAG: @_ZTV1EIlE = linkonce_odr unnamed_addr constant {{.*}}, comdat,
-// CHECK-DAG: @_ZTS1EIlE = linkonce_odr constant {{.*}}, comdat{{$}}
+// CHECK-DAG: @_ZTS1EIlE = linkonce_odr constant {{.*}}, comdat, align 1{{$}}
 // CHECK-DAG: @_ZTI1EIlE = linkonce_odr constant {{.*}}, comdat{{$}}
 
 // F<long> is an implicit template instantiation with no key function,
 // so its vtable should have linkonce_odr linkage.
 // CHECK-DAG: @_ZTV1FIlE = linkonce_odr unnamed_addr constant {{.*}}, comdat,
-// CHECK-DAG: @_ZTS1FIlE = linkonce_odr constant {{.*}}, comdat{{$}}
+// CHECK-DAG: @_ZTS1FIlE = linkonce_odr constant {{.*}}, comdat, align 1{{$}}
 // CHECK-DAG: @_ZTI1FIlE = linkonce_odr constant {{.*}}, comdat{{$}}
 
 // F<int> is an explicit template instantiation declaration without a
@@ -171,7 +171,7 @@
 // F<char> is an explicit specialization without a key function, so
 // its vtable should have linkonce_odr linkage.
 // CHECK-DAG: @_ZTV1FIcE = linkonce_odr unnamed_addr constant {{.*}}, comdat,
-// CHECK-DAG: @_ZTS1FIcE = linkonce_odr constant {{.*}}, comdat{{$}}
+// CHECK-DAG: @_ZTS1FIcE = linkonce_odr constant {{.*}}, comdat, align 1{{$}}
 // CHECK-DAG: @_ZTI1FIcE = linkonce_odr constant {{.*}}, comdat{{$}}
 
 // CHECK-DAG: @_ZTV1GIiE = linkonce_odr unnamed_addr constant {{.*}}, comdat,
Index: test/CodeGenCXX/vtable-align.cpp
===================================================================
--- test/CodeGenCXX/vtable-align.cpp
+++ test/CodeGenCXX/vtable-align.cpp
@@ -10,5 +10,6 @@
 void A::f() {}
 
 // CHECK-32: @_ZTV1A = unnamed_addr constant { [5 x i8*] } { [5 x i8*] [i8* null, i8* bitcast ({ i8*, i8* }* @_ZTI1A to i8*), i8* bitcast (void (%struct.A*)* @_ZN1A1fEv to i8*), i8* bitcast (void (%struct.A*)* @_ZN1A1gEv to i8*), i8* bitcast (void (%struct.A*)* @_ZN1A1hEv to i8*)] }, align 4
-
+// CHECK-32: @_ZTS1A = constant [3 x i8] c"1A\00", align 1
 // CHECK-64: @_ZTV1A = unnamed_addr constant { [5 x i8*] } { [5 x i8*] [i8* null, i8* bitcast ({ i8*, i8* }* @_ZTI1A to i8*), i8* bitcast (void (%struct.A*)* @_ZN1A1fEv to i8*), i8* bitcast (void (%struct.A*)* @_ZN1A1gEv to i8*), i8* bitcast (void (%struct.A*)* @_ZN1A1hEv to i8*)] }, align 8
+// CHECK-64: @_ZTS1A = constant [3 x i8] c"1A\00", align 1
Index: lib/CodeGen/ItaniumCXXABI.cpp
===================================================================
--- lib/CodeGen/ItaniumCXXABI.cpp
+++ lib/CodeGen/ItaniumCXXABI.cpp
@@ -2730,6 +2730,7 @@
     CGM.CreateOrReplaceCXXRuntimeVariable(Name, Init->getType(), Linkage);
 
   GV->setInitializer(Init);
+  GV->setAlignment(1); // prevent over-aligning the string
 
   return GV;
 }


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