align the current stack frame to something larger than the default, when necessary

Author: kripken

lib/Target/JSBackend/AllocaManager.cpp

@@ -40,8 +40,10 @@ uint64_t AllocaManager::getSize(const AllocaInst *AI) {
 // Return the alignment of the given alloca.
 unsigned AllocaManager::getAlignment(const AllocaInst *AI) {
   assert(AI->isStaticAlloca());
-  return std::max(AI->getAlignment(),
-                  DL->getABITypeAlignment(AI->getAllocatedType()));
+  unsigned Alignment = std::max(AI->getAlignment(),
+                                DL->getABITypeAlignment(AI->getAllocatedType()));
+  MaxAlignment = std::max(Alignment, MaxAlignment);
+  return Alignment;
 }
 
 AllocaManager::AllocaInfo AllocaManager::getInfo(const AllocaInst *AI) {
@@ -452,7 +454,7 @@ void AllocaManager::computeFrameOffsets() {
                   "Statically allocated frame size is " << FrameSize << "\n");
 }
 
-AllocaManager::AllocaManager() {
+AllocaManager::AllocaManager() : MaxAlignment(0) {
 }
 
 void AllocaManager::analyze(const Function &Func, const DataLayout &Layout,

lib/Target/JSBackend/AllocaManager.h

@@ -142,6 +142,8 @@ class AllocaManager {
   void computeRepresentatives();
   void computeFrameOffsets();
 
+  unsigned MaxAlignment;
+
 public:
   AllocaManager();
 
@@ -166,6 +168,9 @@ class AllocaManager {
 
   /// Return the total frame size for all static allocas and associated padding.
   uint64_t getFrameSize() const { return FrameSize; }
+
+  /// Return the largest alignment seen.
+  unsigned getMaxAlignment() const { return MaxAlignment; }
 };
 
 } // namespace llvm

lib/Target/JSBackend/JSBackend.cpp

@@ -1456,10 +1456,14 @@ void JSWriter::generateExpression(const User *I, raw_string_ostream& Code) {
     if (AI->isStaticAlloca()) {
       uint64_t Offset;
       if (Allocas.getFrameOffset(AI, &Offset)) {
-        if (Offset != 0) {
-          Code << getAssign(AI) << "sp + " << Offset << "|0";
+        Code << getAssign(AI);
+        if (Allocas.getMaxAlignment() <= STACK_ALIGN) {
+          Code << "sp";
         } else {
-          Code << getAssign(AI) << "sp";
+          Code << "sp_a"; // aligned base of stack is different, use that
+        }
+        if (Offset != 0) {
+          Code << " + " << Offset << "|0";
         }
         break;
       }
@@ -1468,6 +1472,8 @@ void JSWriter::generateExpression(const User *I, raw_string_ostream& Code) {
       return;
     }
 
+    assert(AI->getAlignment() <= STACK_ALIGN); // TODO
+
     Type *T = AI->getAllocatedType();
     std::string Size;
     uint64_t BaseSize = DL->getTypeAllocSize(T);
@@ -1822,6 +1828,10 @@ void JSWriter::printFunctionBody(const Function *F) {
 
   // Emit local variables
   UsedVars["sp"] = Type::IntegerTyID;
+  unsigned MaxAlignment = Allocas.getMaxAlignment();
+  if (MaxAlignment > STACK_ALIGN) {
+    UsedVars["sp_a"] = Type::IntegerTyID;
+  }
   UsedVars["label"] = Type::IntegerTyID;
   if (!UsedVars.empty()) {
     unsigned Count = 0;
@@ -1864,6 +1874,11 @@ void JSWriter::printFunctionBody(const Function *F) {
   // Emit stack entry
   Out << " " << getAdHocAssign("sp", Type::getInt32Ty(F->getContext())) << "STACKTOP;";
   if (uint64_t FrameSize = Allocas.getFrameSize()) {
+    if (MaxAlignment > STACK_ALIGN) {
+      // We must align this entire stack frame to something higher than the default
+      Out << "\n ";
+      Out << "sp_a = STACKTOP = (STACKTOP + " << utostr(MaxAlignment-1) << ")&-" << utostr(MaxAlignment) << ";";
+    }
     Out << "\n ";
     Out << getStackBump(FrameSize);
   }