[GlobalMerge] Allow merging globals with arbitrary alignment.

Instead of depending on implicit padding from the structure layout code,
use a packed struct and emit the padding explicitly.

Differential Revision: https://reviews.llvm.org/D49710

llvm-svn: 337961

lib/CodeGen/GlobalMerge.cpp

@@ -440,6 +440,7 @@ bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
   assert(Globals.size() > 1);
 
   Type *Int32Ty = Type::getInt32Ty(M.getContext());
+  Type *Int8Ty = Type::getInt8Ty(M.getContext());
   auto &DL = M.getDataLayout();
 
   LLVM_DEBUG(dbgs() << " Trying to merge set, starts with #"
@@ -452,17 +453,31 @@ bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
     uint64_t MergedSize = 0;
     std::vector<Type*> Tys;
     std::vector<Constant*> Inits;
+    std::vector<unsigned> StructIdxs;
 
     bool HasExternal = false;
     StringRef FirstExternalName;
+    unsigned MaxAlign = 1;
+    unsigned CurIdx = 0;
     for (j = i; j != -1; j = GlobalSet.find_next(j)) {
       Type *Ty = Globals[j]->getValueType();
+      unsigned Align = DL.getPreferredAlignment(Globals[j]);
+      unsigned Padding = alignTo(MergedSize, Align) - MergedSize;
+      MergedSize += Padding;
       MergedSize += DL.getTypeAllocSize(Ty);
       if (MergedSize > MaxOffset) {
         break;
       }
+      if (Padding) {
+        Tys.push_back(ArrayType::get(Int8Ty, Padding));
+        Inits.push_back(ConstantAggregateZero::get(Tys.back()));
+        ++CurIdx;
+      }
       Tys.push_back(Ty);
       Inits.push_back(Globals[j]->getInitializer());
+      StructIdxs.push_back(CurIdx++);
+
+      MaxAlign = std::max(MaxAlign, Align);
 
       if (Globals[j]->hasExternalLinkage() && !HasExternal) {
         HasExternal = true;
@@ -481,7 +496,8 @@ bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
     GlobalValue::LinkageTypes Linkage = HasExternal
                                             ? GlobalValue::ExternalLinkage
                                             : GlobalValue::InternalLinkage;
-    StructType *MergedTy = StructType::get(M.getContext(), Tys);
+    // Use a packed struct so we can control alignment.
+    StructType *MergedTy = StructType::get(M.getContext(), Tys, true);
     Constant *MergedInit = ConstantStruct::get(MergedTy, Inits);
 
     // On Darwin external linkage needs to be preserved, otherwise
@@ -499,13 +515,9 @@ bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
         M, MergedTy, isConst, MergedLinkage, MergedInit, MergedName, nullptr,
         GlobalVariable::NotThreadLocal, AddrSpace);
 
-    const StructLayout *MergedLayout = DL.getStructLayout(MergedTy);
-    // Set the alignment of the merged struct as the maximum alignment of the
-    // globals to prevent over-alignment. We don't handle globals that are not
-    // default aligned, so the alignment of the MergedLayout struct is
-    // equivalent.
-    MergedGV->setAlignment(MergedLayout->getAlignment());
+    MergedGV->setAlignment(MaxAlign);
 
+    const StructLayout *MergedLayout = DL.getStructLayout(MergedTy);
     for (ssize_t k = i, idx = 0; k != j; k = GlobalSet.find_next(k), ++idx) {
       GlobalValue::LinkageTypes Linkage = Globals[k]->getLinkage();
       std::string Name = Globals[k]->getName();
@@ -514,11 +526,12 @@ bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
 
       // Copy metadata while adjusting any debug info metadata by the original
       // global's offset within the merged global.
-      MergedGV->copyMetadata(Globals[k], MergedLayout->getElementOffset(idx));
+      MergedGV->copyMetadata(Globals[k],
+                             MergedLayout->getElementOffset(StructIdxs[idx]));
 
       Constant *Idx[2] = {
           ConstantInt::get(Int32Ty, 0),
-        ConstantInt::get(Int32Ty, idx),
+          ConstantInt::get(Int32Ty, StructIdxs[idx]),
       };
       Constant *GEP =
           ConstantExpr::getInBoundsGetElementPtr(MergedTy, MergedGV, Idx);
@@ -531,8 +544,8 @@ bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals,
       // It's not safe on Mach-O as the alias (and thus the portion of the
       // MergedGlobals variable) may be dead stripped at link time.
       if (Linkage != GlobalValue::InternalLinkage || !IsMachO) {
-        GlobalAlias *GA =
-            GlobalAlias::create(Tys[idx], AddrSpace, Linkage, Name, GEP, &M);
+        GlobalAlias *GA = GlobalAlias::create(Tys[StructIdxs[idx]], AddrSpace,
+                                              Linkage, Name, GEP, &M);
         GA->setDLLStorageClass(DLLStorage);
       }
 
@@ -610,12 +623,6 @@ bool GlobalMerge::doInitialization(Module &M) {
 
     unsigned AddressSpace = PT->getAddressSpace();
 
-    // Ignore fancy-aligned globals for now.
-    unsigned Alignment = DL.getPreferredAlignment(&GV);
-    Type *Ty = GV.getValueType();
-    if (Alignment > DL.getABITypeAlignment(Ty))
-      continue;
-
     // Ignore all 'special' globals.
     if (GV.getName().startswith("llvm.") ||
         GV.getName().startswith(".llvm."))
@@ -625,6 +632,7 @@ bool GlobalMerge::doInitialization(Module &M) {
     if (isMustKeepGlobalVariable(&GV))
       continue;
 
+    Type *Ty = GV.getValueType();
     if (DL.getTypeAllocSize(Ty) < MaxOffset) {
       if (TM &&
           TargetLoweringObjectFile::getKindForGlobal(&GV, *TM).isBSSLocal())

test/Transforms/GlobalMerge/alignment-2.ll

@@ -0,0 +1,22 @@
+; RUN: opt -global-merge -global-merge-max-offset=100 -S -o - %s | FileCheck %s
+
+target datalayout = "e-p:64:64"
+target triple = "x86_64-unknown-linux-gnu"
+
+; This produces align 4, not the obvious align 1, to be consistent with what
+; the AsmPrinter would do.
+; CHECK: @_MergedGlobals = private global <{ [2 x i32], [2 x i32] }> <{ [2 x i32] [i32 1, i32 1], [2 x i32] [i32 2, i32 2] }>, align 4
+
+; CHECK: @a = internal alias [2 x i32], getelementptr inbounds (<{ [2 x i32], [2 x i32] }>, <{ [2 x i32], [2 x i32] }>* @_MergedGlobals, i32 0, i32 0)
+@a = internal global [2 x i32] [i32 1, i32 1], align 1
+
+; CHECK: @b = internal alias [2 x i32], getelementptr inbounds (<{ [2 x i32], [2 x i32] }>, <{ [2 x i32], [2 x i32] }>* @_MergedGlobals, i32 0, i32 1)
+@b = internal global [2 x i32] [i32 2, i32 2], align 1
+
+define void @use() {
+  ; CHECK: load i32, i32* getelementptr inbounds (<{ [2 x i32], [2 x i32] }>, <{ [2 x i32], [2 x i32] }>* @_MergedGlobals, i32 0, i32 0, i32 0)
+  %x = load i32, i32* bitcast ([2 x i32]* @a to i32*)
+  ; CHECK: load i32, i32* getelementptr inbounds (<{ [2 x i32], [2 x i32] }>, <{ [2 x i32], [2 x i32] }>* @_MergedGlobals, i32 0, i32 1, i32 0)
+  %y = load i32, i32* bitcast ([2 x i32]* @b to i32*)
+  ret void
+}

test/Transforms/GlobalMerge/alignment.ll

@@ -0,0 +1,20 @@
+; RUN: opt -global-merge -global-merge-max-offset=100 -S -o - %s | FileCheck %s
+
+target datalayout = "e-p:64:64"
+target triple = "x86_64-unknown-linux-gnu"
+
+; CHECK: @_MergedGlobals = private global <{ [5 x i8], [3 x i8], [2 x i32] }> <{ [5 x i8] c"\01\01\01\01\01", [3 x i8] zeroinitializer, [2 x i32] [i32 2, i32 2] }>, align 4
+
+; CHECK: @a = internal alias [5 x i8], getelementptr inbounds (<{ [5 x i8], [3 x i8], [2 x i32] }>, <{ [5 x i8], [3 x i8], [2 x i32] }>* @_MergedGlobals, i32 0, i32 0)
+@a = internal global [5 x i8] [i8 1, i8 1, i8 1, i8 1, i8 1], align 4
+
+; CHECK: @b = internal alias [2 x i32], getelementptr inbounds (<{ [5 x i8], [3 x i8], [2 x i32] }>, <{ [5 x i8], [3 x i8], [2 x i32] }>* @_MergedGlobals, i32 0, i32 2)
+@b = internal global [2 x i32] [i32 2, i32 2]
+
+define void @use() {
+  ; CHECK: load i32, i32* bitcast (<{ [5 x i8], [3 x i8], [2 x i32] }>* @_MergedGlobals to i32*)
+  %x = load i32, i32* bitcast ([5 x i8]* @a to i32*)
+  ; CHECK: load i32, i32* getelementptr inbounds (<{ [5 x i8], [3 x i8], [2 x i32] }>, <{ [5 x i8], [3 x i8], [2 x i32] }>* @_MergedGlobals, i32 0, i32 2, i32 0)
+  %y = load i32, i32* bitcast ([2 x i32]* @b to i32*)
+  ret void
+}

test/Transforms/GlobalMerge/basic.ll

@@ -3,18 +3,18 @@
 target datalayout = "e-p:64:64"
 target triple = "x86_64-unknown-linux-gnu"
 
-; CHECK: @_MergedGlobals = private global { i32, i32 } { i32 1, i32 2 }
+; CHECK: @_MergedGlobals = private global <{ i32, i32 }> <{ i32 1, i32 2 }>, align 4
 
-; CHECK: @a = internal alias i32, getelementptr inbounds ({ i32, i32 }, { i32, i32 }* @_MergedGlobals, i32 0, i32 0)
+; CHECK: @a = internal alias i32, getelementptr inbounds (<{ i32, i32 }>, <{ i32, i32 }>* @_MergedGlobals, i32 0, i32 0)
 @a = internal global i32 1
 
-; CHECK: @b = internal alias i32, getelementptr inbounds ({ i32, i32 }, { i32, i32 }* @_MergedGlobals, i32 0, i32 1)
+; CHECK: @b = internal alias i32, getelementptr inbounds (<{ i32, i32 }>, <{ i32, i32 }>* @_MergedGlobals, i32 0, i32 1)
 @b = internal global i32 2
 
 define void @use() {
-  ; CHECK: load i32, i32* getelementptr inbounds ({ i32, i32 }, { i32, i32 }* @_MergedGlobals, i32 0, i32 0)
+  ; CHECK: load i32, i32* getelementptr inbounds (<{ i32, i32 }>, <{ i32, i32 }>* @_MergedGlobals, i32 0, i32 0)
   %x = load i32, i32* @a
-  ; CHECK: load i32, i32* getelementptr inbounds ({ i32, i32 }, { i32, i32 }* @_MergedGlobals, i32 0, i32 1)
+  ; CHECK: load i32, i32* getelementptr inbounds (<{ i32, i32 }>, <{ i32, i32 }>* @_MergedGlobals, i32 0, i32 1)
   %y = load i32, i32* @b
   ret void
 }

test/Transforms/GlobalMerge/debug-info.ll

@@ -3,7 +3,7 @@
 source_filename = "test/Transforms/GlobalMerge/debug-info.ll"
 target datalayout = "e-p:64:64"
 target triple = "x86_64-unknown-linux-gnu"
-; CHECK: @_MergedGlobals = private global { i32, i32 } { i32 1, i32 2 }, align 4, !dbg [[A:![0-9]+]], !dbg [[B:![0-9]+]]
+; CHECK: @_MergedGlobals = private global <{ i32, i32 }> <{ i32 1, i32 2 }>, align 4, !dbg [[A:![0-9]+]], !dbg [[B:![0-9]+]]
 
 @a = internal global i32 1, !dbg !0
 @b = internal global i32 2, !dbg !2