Add support for GEPs with global ptr operands. Add support for loads with constexpr GEPs

Author: farzonl

llvm/lib/Target/DirectX/DXILLegalizePass.cpp

@@ -87,9 +87,8 @@ static void fixI8UseChain(Instruction &I,
     return;
   }
 
-  if (auto *Load = dyn_cast<LoadInst>(&I)) {
-    if (!I.getType()->isIntegerTy(8))
-      return;
+  if (auto *Load = dyn_cast<LoadInst>(&I);
+      Load && I.getType()->isIntegerTy(8)) {
     SmallVector<Value *> NewOperands;
     ProcessOperands(NewOperands);
     Type *ElementType = NewOperands[0]->getType();
@@ -103,6 +102,31 @@ static void fixI8UseChain(Instruction &I,
     return;
   }
 
+  if (auto *Load = dyn_cast<LoadInst>(&I);
+      Load && isa<ConstantExpr>(Load->getPointerOperand())) {
+    auto *CE = dyn_cast<ConstantExpr>(Load->getPointerOperand());
+    if (!(CE->getOpcode() == Instruction::GetElementPtr))
+      return;
+    auto *GEP = dyn_cast<GEPOperator>(CE);
+    if (!GEP->getSourceElementType()->isIntegerTy(8))
+      return;
+
+    Type *ElementType = Load->getType();
+    ConstantInt *Offset = dyn_cast<ConstantInt>(GEP->getOperand(1));
+    uint32_t ByteOffset = Offset->getZExtValue();
+    uint32_t ElemSize = Load->getDataLayout().getTypeAllocSize(ElementType);
+    uint32_t Index = ByteOffset / ElemSize;
+    Value *NewGEP = Builder.CreateGEP(ElementType, GEP->getPointerOperand(),
+                                      Builder.getInt32(Index), GEP->getName(),
+                                      GEP->getNoWrapFlags());
+
+    LoadInst *NewLoad = Builder.CreateLoad(ElementType, NewGEP);
+    ReplacedValues[Load] = NewLoad;
+    Load->replaceAllUsesWith(NewLoad);
+    ToRemove.push_back(Load);
+    return;
+  }
+
   if (auto *BO = dyn_cast<BinaryOperator>(&I)) {
     if (!I.getType()->isIntegerTy(8))
       return;
@@ -178,6 +202,8 @@ static void fixI8UseChain(Instruction &I,
     Type *ElementType = BasePtr->getType();
     if (auto *AI = dyn_cast<AllocaInst>(BasePtr))
       ElementType = AI->getAllocatedType();
+    if (auto *GV = dyn_cast<GlobalVariable>(BasePtr))
+      ElementType = GV->getValueType();
     if (auto *ArrTy = dyn_cast<ArrayType>(ElementType))
       ElementType = ArrTy->getArrayElementType();
 

llvm/test/CodeGen/DirectX/legalize-i8.ll

@@ -160,3 +160,19 @@ define i32 @i8_gep_store() {
   %4 = sext i8 %3 to i32
   ret i32 %4
 }
+
+@g = local_unnamed_addr addrspace(3) global [2 x float] zeroinitializer, align 4
+define float @i8_gep_global_index() {
+  ; CHECK-LABEL: define i32 @i8_gep_global_index(
+  ; CHECK-NEXT: %2 = load float, ptr addrspace(3) getelementptr inbounds nuw (float, ptr addrspace(3) @g, i32 1), align 4
+  %1 = getelementptr inbounds nuw i8, ptr addrspace(3) @g, i32 4
+  %2 = load float, ptr addrspace(3) %1, align 4
+  ret float %2
+}
+
+define float @i8_gep_global_constexpr() {
+  ; CHECK-LABEL: define i32 @i8_gep_global_constexpr(
+  ; CHECK-NEXT: %2 = load float, ptr addrspace(3) getelementptr inbounds nuw (float, ptr addrspace(3) @g, i32 1), align 4
+  %1 = load float, ptr addrspace(3) getelementptr inbounds nuw (i8, ptr addrspace(3) @g, i32 4), align 4
+  ret float %1
+}