WholeProgramDevirt: Teach the pass to respect the global's alignment.

The bytes inserted before an overaligned global need to be padded according
to the alignment set on the original global in order for the initializer
to meet the global's alignment requirements. The previous implementation
that padded to the pointer width happened to be correct for vtables on most
platforms but may do the wrong thing if the vtable has a larger alignment.

This issue is visible with a prototype implementation of HWASAN for globals,
which will overalign all globals including vtables to 16 bytes.

There is also no padding requirement for the bytes inserted after the global
because they are never read from nor are they significant for alignment
purposes, so stop inserting padding there.

Differential Revision: https://reviews.llvm.org/D65031

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@366725 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/IPO/WholeProgramDevirt.cpp b/lib/Transforms/IPO/WholeProgramDevirt.cpp
index 6b6dd6194e179ca8aef3c572480633bd92c56691..6bbcba94b000612a1fa64f0627beb729f55e9be9 100644 (file)
--- a/lib/Transforms/IPO/WholeProgramDevirt.cpp
+++ b/lib/Transforms/IPO/WholeProgramDevirt.cpp
@@ -1302,10 +1302,12 @@ void DevirtModule::rebuildGlobal(VTableBits &B) {
   if (B.Before.Bytes.empty() && B.After.Bytes.empty())
     return;
 
-  // Align each byte array to pointer width.
-  unsigned PointerSize = M.getDataLayout().getPointerSize();
-  B.Before.Bytes.resize(alignTo(B.Before.Bytes.size(), PointerSize));
-  B.After.Bytes.resize(alignTo(B.After.Bytes.size(), PointerSize));
+  // Align the before byte array to the global's minimum alignment so that we
+  // don't break any alignment requirements on the global.
+  unsigned Align = B.GV->getAlignment();
+  if (Align == 0)
+    Align = M.getDataLayout().getABITypeAlignment(B.GV->getValueType());
+  B.Before.Bytes.resize(alignTo(B.Before.Bytes.size(), Align));
 
   // Before was stored in reverse order; flip it now.
   for (size_t I = 0, Size = B.Before.Bytes.size(); I != Size / 2; ++I)
@@ -1322,6 +1324,7 @@ void DevirtModule::rebuildGlobal(VTableBits &B) {
                          GlobalVariable::PrivateLinkage, NewInit, "", B.GV);
   NewGV->setSection(B.GV->getSection());
   NewGV->setComdat(B.GV->getComdat());
+  NewGV->setAlignment(B.GV->getAlignment());
 
   // Copy the original vtable's metadata to the anonymous global, adjusting
   // offsets as required.

diff --git a/test/Transforms/WholeProgramDevirt/virtual-const-prop-begin.ll b/test/Transforms/WholeProgramDevirt/virtual-const-prop-begin.ll
index 63549e8540c33a3c67cac11b1c32599603a7e2ed..6e55235ebfcd823834fd641da419fa6f20808fbf 100644 (file)
--- a/test/Transforms/WholeProgramDevirt/virtual-const-prop-begin.ll
+++ b/test/Transforms/WholeProgramDevirt/virtual-const-prop-begin.ll
@@ -17,19 +17,19 @@ i8* bitcast (i1 (i8*)* @vf0i1 to i8*),
 i8* bitcast (i32 (i8*)* @vf2i32 to i8*)
 ], !type !0
 
-; CHECK: [[VT3DATA:@[^ ]*]] = private constant { [8 x i8], [3 x i8*], [0 x i8] } { [8 x i8] c"\00\00\00\01\03\00\00\00", [3 x i8*] [i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i32 (i8*)* @vf3i32 to i8*)], [0 x i8] zeroinitializer }, !type [[T8]]
+; CHECK: [[VT3DATA:@[^ ]*]] = private constant { [5 x i8], [3 x i8*], [0 x i8] } { [5 x i8] c"\01\03\00\00\00", [3 x i8*] [i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i32 (i8*)* @vf3i32 to i8*)], [0 x i8] zeroinitializer }, align 1, !type [[T5:![0-9]+]]
 @vt3 = constant [3 x i8*] [
 i8* bitcast (i1 (i8*)* @vf0i1 to i8*),
 i8* bitcast (i1 (i8*)* @vf1i1 to i8*),
 i8* bitcast (i32 (i8*)* @vf3i32 to i8*)
-], !type !0
+], align 1, !type !0
 
-; CHECK: [[VT4DATA:@[^ ]*]] = private constant { [8 x i8], [3 x i8*], [0 x i8] } { [8 x i8] c"\00\00\00\02\04\00\00\00", [3 x i8*] [i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i32 (i8*)* @vf4i32 to i8*)], [0 x i8] zeroinitializer }, !type [[T8]]
+; CHECK: [[VT4DATA:@[^ ]*]] = private constant { [16 x i8], [3 x i8*], [0 x i8] } { [16 x i8] c"\00\00\00\00\00\00\00\00\00\00\00\02\04\00\00\00", [3 x i8*] [i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i32 (i8*)* @vf4i32 to i8*)], [0 x i8] zeroinitializer },  align 16, !type [[T16:![0-9]+]]
 @vt4 = constant [3 x i8*] [
 i8* bitcast (i1 (i8*)* @vf1i1 to i8*),
 i8* bitcast (i1 (i8*)* @vf0i1 to i8*),
 i8* bitcast (i32 (i8*)* @vf4i32 to i8*)
-], !type !0
+], align 16, !type !0
 
 ; CHECK: @vt5 = {{.*}}, !type [[T0:![0-9]+]]
 @vt5 = constant [3 x i8*] [
@@ -40,8 +40,8 @@ i8* bitcast (void ()* @__cxa_pure_virtual to i8*)
 
 ; CHECK: @vt1 = alias [3 x i8*], getelementptr inbounds ({ [8 x i8], [3 x i8*], [0 x i8] }, { [8 x i8], [3 x i8*], [0 x i8] }* [[VT1DATA]], i32 0, i32 1)
 ; CHECK: @vt2 = alias [3 x i8*], getelementptr inbounds ({ [8 x i8], [3 x i8*], [0 x i8] }, { [8 x i8], [3 x i8*], [0 x i8] }* [[VT2DATA]], i32 0, i32 1)
-; CHECK: @vt3 = alias [3 x i8*], getelementptr inbounds ({ [8 x i8], [3 x i8*], [0 x i8] }, { [8 x i8], [3 x i8*], [0 x i8] }* [[VT3DATA]], i32 0, i32 1)
-; CHECK: @vt4 = alias [3 x i8*], getelementptr inbounds ({ [8 x i8], [3 x i8*], [0 x i8] }, { [8 x i8], [3 x i8*], [0 x i8] }* [[VT4DATA]], i32 0, i32 1)
+; CHECK: @vt3 = alias [3 x i8*], getelementptr inbounds ({ [5 x i8], [3 x i8*], [0 x i8] }, { [5 x i8], [3 x i8*], [0 x i8] }* [[VT3DATA]], i32 0, i32 1)
+; CHECK: @vt4 = alias [3 x i8*], getelementptr inbounds ({ [16 x i8], [3 x i8*], [0 x i8] }, { [16 x i8], [3 x i8*], [0 x i8] }* [[VT4DATA]], i32 0, i32 1)
 
 define i1 @vf0i1(i8* %this) readnone {
   ret i1 0
@@ -134,6 +134,8 @@ declare void @llvm.assume(i1)
 declare void @__cxa_pure_virtual()
 
 ; CHECK: [[T8]] = !{i32 8, !"typeid"}
+; CHECK: [[T5]] = !{i32 5, !"typeid"}
+; CHECK: [[T16]] = !{i32 16, !"typeid"}
 ; CHECK: [[T0]] = !{i32 0, !"typeid"}
 
 !0 = !{i32 0, !"typeid"}

diff --git a/test/Transforms/WholeProgramDevirt/virtual-const-prop-end.ll b/test/Transforms/WholeProgramDevirt/virtual-const-prop-end.ll
index 3d61e1e20822a2b9d63fe3d671beb243acec0671..5ab9571a0caadf21097d5c2f43c8fec0760b54c4 100644 (file)
--- a/test/Transforms/WholeProgramDevirt/virtual-const-prop-end.ll
+++ b/test/Transforms/WholeProgramDevirt/virtual-const-prop-end.ll
@@ -3,7 +3,7 @@
 target datalayout = "e-p:64:64"
 target triple = "x86_64-unknown-linux-gnu"
 
-; CHECK: [[VT1DATA:@[^ ]*]] = private constant { [0 x i8], [4 x i8*], [8 x i8] } { [0 x i8] zeroinitializer, [4 x i8*] [i8* null, i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i32 (i8*)* @vf1i32 to i8*)], [8 x i8] c"\01\00\00\00\01\00\00\00" }, !type [[T8:![0-9]+]]
+; CHECK: [[VT1DATA:@[^ ]*]] = private constant { [0 x i8], [4 x i8*], [5 x i8] } { [0 x i8] zeroinitializer, [4 x i8*] [i8* null, i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i32 (i8*)* @vf1i32 to i8*)], [5 x i8] c"\01\00\00\00\01" }, !type [[T8:![0-9]+]]
 @vt1 = constant [4 x i8*] [
 i8* null,
 i8* bitcast (i1 (i8*)* @vf0i1 to i8*),
@@ -11,14 +11,14 @@ i8* bitcast (i1 (i8*)* @vf1i1 to i8*),
 i8* bitcast (i32 (i8*)* @vf1i32 to i8*)
 ], !type !1
 
-; CHECK: [[VT2DATA:@[^ ]*]] = private constant { [0 x i8], [3 x i8*], [8 x i8] } { [0 x i8] zeroinitializer, [3 x i8*] [i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i32 (i8*)* @vf2i32 to i8*)], [8 x i8] c"\02\00\00\00\02\00\00\00" }, !type [[T0:![0-9]+]]
+; CHECK: [[VT2DATA:@[^ ]*]] = private constant { [0 x i8], [3 x i8*], [5 x i8] } { [0 x i8] zeroinitializer, [3 x i8*] [i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i32 (i8*)* @vf2i32 to i8*)], [5 x i8] c"\02\00\00\00\02" }, !type [[T0:![0-9]+]]
 @vt2 = constant [3 x i8*] [
 i8* bitcast (i1 (i8*)* @vf1i1 to i8*),
 i8* bitcast (i1 (i8*)* @vf0i1 to i8*),
 i8* bitcast (i32 (i8*)* @vf2i32 to i8*)
 ], !type !0
 
-; CHECK: [[VT3DATA:@[^ ]*]] = private constant { [0 x i8], [4 x i8*], [8 x i8] } { [0 x i8] zeroinitializer, [4 x i8*] [i8* null, i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i32 (i8*)* @vf3i32 to i8*)], [8 x i8] c"\03\00\00\00\01\00\00\00" }, !type [[T8]]
+; CHECK: [[VT3DATA:@[^ ]*]] = private constant { [0 x i8], [4 x i8*], [5 x i8] } { [0 x i8] zeroinitializer, [4 x i8*] [i8* null, i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i32 (i8*)* @vf3i32 to i8*)], [5 x i8] c"\03\00\00\00\01" }, !type [[T8]]
 @vt3 = constant [4 x i8*] [
 i8* null,
 i8* bitcast (i1 (i8*)* @vf0i1 to i8*),
@@ -26,17 +26,17 @@ i8* bitcast (i1 (i8*)* @vf1i1 to i8*),
 i8* bitcast (i32 (i8*)* @vf3i32 to i8*)
 ], !type !1
 
-; CHECK: [[VT4DATA:@[^ ]*]] = private constant { [0 x i8], [3 x i8*], [8 x i8] } { [0 x i8] zeroinitializer, [3 x i8*] [i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i32 (i8*)* @vf4i32 to i8*)], [8 x i8] c"\04\00\00\00\02\00\00\00" }, !type [[T0]]
+; CHECK: [[VT4DATA:@[^ ]*]] = private constant { [0 x i8], [3 x i8*], [5 x i8] } { [0 x i8] zeroinitializer, [3 x i8*] [i8* bitcast (i1 (i8*)* @vf1i1 to i8*), i8* bitcast (i1 (i8*)* @vf0i1 to i8*), i8* bitcast (i32 (i8*)* @vf4i32 to i8*)], [5 x i8] c"\04\00\00\00\02" }, !type [[T0]]
 @vt4 = constant [3 x i8*] [
 i8* bitcast (i1 (i8*)* @vf1i1 to i8*),
 i8* bitcast (i1 (i8*)* @vf0i1 to i8*),
 i8* bitcast (i32 (i8*)* @vf4i32 to i8*)
 ], !type !0
 
-; CHECK: @vt1 = alias [4 x i8*], getelementptr inbounds ({ [0 x i8], [4 x i8*], [8 x i8] }, { [0 x i8], [4 x i8*], [8 x i8] }* [[VT1DATA]], i32 0, i32 1)
-; CHECK: @vt2 = alias [3 x i8*], getelementptr inbounds ({ [0 x i8], [3 x i8*], [8 x i8] }, { [0 x i8], [3 x i8*], [8 x i8] }* [[VT2DATA]], i32 0, i32 1)
-; CHECK: @vt3 = alias [4 x i8*], getelementptr inbounds ({ [0 x i8], [4 x i8*], [8 x i8] }, { [0 x i8], [4 x i8*], [8 x i8] }* [[VT3DATA]], i32 0, i32 1)
-; CHECK: @vt4 = alias [3 x i8*], getelementptr inbounds ({ [0 x i8], [3 x i8*], [8 x i8] }, { [0 x i8], [3 x i8*], [8 x i8] }* [[VT4DATA]], i32 0, i32 1)
+; CHECK: @vt1 = alias [4 x i8*], getelementptr inbounds ({ [0 x i8], [4 x i8*], [5 x i8] }, { [0 x i8], [4 x i8*], [5 x i8] }* [[VT1DATA]], i32 0, i32 1)
+; CHECK: @vt2 = alias [3 x i8*], getelementptr inbounds ({ [0 x i8], [3 x i8*], [5 x i8] }, { [0 x i8], [3 x i8*], [5 x i8] }* [[VT2DATA]], i32 0, i32 1)
+; CHECK: @vt3 = alias [4 x i8*], getelementptr inbounds ({ [0 x i8], [4 x i8*], [5 x i8] }, { [0 x i8], [4 x i8*], [5 x i8] }* [[VT3DATA]], i32 0, i32 1)
+; CHECK: @vt4 = alias [3 x i8*], getelementptr inbounds ({ [0 x i8], [3 x i8*], [5 x i8] }, { [0 x i8], [3 x i8*], [5 x i8] }* [[VT4DATA]], i32 0, i32 1)
 
 define i1 @vf0i1(i8* %this) readnone {
   ret i1 0