address pr comments, make loop in collectIndicesAndDimsFromGEP clearer by not using getOperand

Author: farzonl

llvm/lib/Target/DirectX/DXILFlattenArrays.cpp

@@ -229,20 +229,17 @@ void DXILFlattenArraysVisitor::collectIndicesAndDimsFromGEP(
     GetElementPtrInst &GEP, SmallVectorImpl<Value *> &Indices,
     SmallVectorImpl<uint64_t> &Dims, bool &AllIndicesAreConstInt) {
 
-  // Skip the first index which is array ptr
-  // and collect all subsequent indices
   Type *CurrentType = GEP.getSourceElementType();
-  for (unsigned I = 1; I < GEP.getNumIndices(); ++I) {
-    Value *Index = GEP.getOperand(I + 1); // +1 because operand 0 is the pointer
-    AllIndicesAreConstInt &= isa<ConstantInt>(Index);
+
+  // Note index 0 is the ptr index.
+  for (Value *Index : llvm::drop_begin(GEP.indices(), 1)) {
     Indices.push_back(Index);
+    AllIndicesAreConstInt &= isa<ConstantInt>(Index);
 
-    // Get the dimension size for this index
     if (auto *ArrayTy = dyn_cast<ArrayType>(CurrentType)) {
       Dims.push_back(ArrayTy->getNumElements());
       CurrentType = ArrayTy->getElementType();
     } else {
-      // This shouldn't happen for well-formed GEPs
       assert(false && "Expected array type in GEP chain");
     }
   }

llvm/test/CodeGen/DirectX/flatten-array.ll

@@ -221,10 +221,10 @@ define void @gep_4d_index_test()  {
     ; CHECK-NEXT: getelementptr inbounds [16 x i32], ptr %.1dim, i32 0, i32 15
     ; CHECK-NEXT:    ret void
     %1 = alloca [2x[2 x[2 x [2 x i32]]]], align 4
-    %2 = getelementptr inbounds [2x[2 x[2 x [2 x i32]]]], [2x[2 x[2 x [2 x i32]]]]* %1, i32 0, i32 0, i32 0, i32 0, i32 1
-    %3 = getelementptr inbounds [2x[2 x[2 x [2 x i32]]]], [2x[2 x[2 x [2 x i32]]]]* %1, i32 0, i32 0, i32 0, i32 1, i32 1
-    %4 = getelementptr inbounds [2x[2 x[2 x [2 x i32]]]], [2x[2 x[2 x [2 x i32]]]]* %1, i32 0, i32 0, i32 1, i32 1, i32 1
-    %5 = getelementptr inbounds [2x[2 x[2 x [2 x i32]]]], [2x[2 x[2 x [2 x i32]]]]* %1, i32 0, i32 1, i32 1, i32 1, i32 1
+    %2 = getelementptr inbounds [2 x [2 x[2 x [2 x i32]]]], [2 x [2 x [2 x [2 x i32]]]]* %1, i32 0, i32 0, i32 0, i32 0, i32 1
+    %3 = getelementptr inbounds [2 x [2 x[2 x [2 x i32]]]], [2 x [2 x [2 x [2 x i32]]]]* %1, i32 0, i32 0, i32 0, i32 1, i32 1
+    %4 = getelementptr inbounds [2 x [2 x[2 x [2 x i32]]]], [2 x [2 x [2 x [2 x i32]]]]* %1, i32 0, i32 0, i32 1, i32 1, i32 1
+    %5 = getelementptr inbounds [2 x [2 x[2 x [2 x i32]]]], [2 x [2 x [2 x [2 x i32]]]]* %1, i32 0, i32 1, i32 1, i32 1, i32 1
     ret void
 }
 
@@ -234,22 +234,22 @@ define void @gep_4d_index_and_gep_chain_mixed() {
   ; CHECK-COUNT-16: getelementptr inbounds [16 x i32], ptr [[ALLOCA]], i32 0, i32 {{[0-9]|1[0-5]}}
   ; CHECK-NEXT: ret void
   %1 = alloca [2x[2 x[2 x [2 x i32]]]], align 4
-  %a4d0_0 = getelementptr inbounds [2x[2 x[2 x [2 x i32]]]], [2x[2 x[2 x [2 x i32]]]]* %1, i32 0, i32 0, i32 0
+  %a4d0_0 = getelementptr inbounds [2 x [2 x [2 x [2 x i32]]]], [2 x [2 x[2 x [2 x i32]]]]* %1, i32 0, i32 0, i32 0
   %a2d0_0 = getelementptr inbounds [2 x [2 x i32]], [2 x [2 x i32]]* %a4d0_0, i32 0, i32 0, i32 0
   %a2d0_1 = getelementptr inbounds [2 x [2 x i32]], [2 x [2 x i32]]* %a4d0_0, i32 0, i32 0, i32 1
   %a2d1_0 = getelementptr inbounds [2 x [2 x i32]], [2 x [2 x i32]]* %a4d0_0, i32 0, i32 1, i32 0
   %a2d1_1 = getelementptr inbounds [2 x [2 x i32]], [2 x [2 x i32]]* %a4d0_0, i32 0, i32 1, i32 1
-  %b4d0_1 = getelementptr inbounds [2x[2 x[2 x [2 x i32]]]], [2x[2 x[2 x [2 x i32]]]]* %1, i32 0, i32 0, i32 1
+  %b4d0_1 = getelementptr inbounds [2 x [2 x [2 x [2 x i32]]]], [2 x [2 x [2 x [2 x i32]]]]* %1, i32 0, i32 0, i32 1
   %b2d0_0 = getelementptr inbounds [2 x [2 x i32]], [2 x [2 x i32]]* %b4d0_1, i32 0, i32 0, i32 0
   %b2d0_1 = getelementptr inbounds [2 x [2 x i32]], [2 x [2 x i32]]* %b4d0_1, i32 0, i32 0, i32 1
   %b2d1_0 = getelementptr inbounds [2 x [2 x i32]], [2 x [2 x i32]]* %b4d0_1, i32 0, i32 1, i32 0
   %b2d1_1 = getelementptr inbounds [2 x [2 x i32]], [2 x [2 x i32]]* %b4d0_1, i32 0, i32 1, i32 1
-  %c4d1_0 = getelementptr inbounds [2x[2 x[2 x [2 x i32]]]], [2x[2 x[2 x [2 x i32]]]]* %1, i32 0, i32 1, i32 0
+  %c4d1_0 = getelementptr inbounds [2 x [2 x [2 x [2 x i32]]]], [2 x [2 x [2 x [2 x i32]]]]* %1, i32 0, i32 1, i32 0
   %c2d0_0 = getelementptr inbounds [2 x [2 x i32]], [2 x [2 x i32]]* %c4d1_0, i32 0, i32 0, i32 0
   %c2d0_1 = getelementptr inbounds [2 x [2 x i32]], [2 x [2 x i32]]* %c4d1_0, i32 0, i32 0, i32 1
   %c2d1_0 = getelementptr inbounds [2 x [2 x i32]], [2 x [2 x i32]]* %c4d1_0, i32 0, i32 1, i32 0
   %c2d1_1 = getelementptr inbounds [2 x [2 x i32]], [2 x [2 x i32]]* %c4d1_0, i32 0, i32 1, i32 1
-  %g4d1_1 = getelementptr inbounds [2x[2 x[2 x [2 x i32]]]], [2x[2 x[2 x [2 x i32]]]]* %1, i32 0, i32 1, i32 1
+  %g4d1_1 = getelementptr inbounds [2 x [2 x [2 x [2 x i32]]]], [2 x [2 x [2 x [2 x i32]]]]* %1, i32 0, i32 1, i32 1
   %g2d0_0 = getelementptr inbounds [2 x [2 x i32]], [2 x [2 x i32]]* %g4d1_1, i32 0, i32 0, i32 0
   %g2d0_1 = getelementptr inbounds [2 x [2 x i32]], [2 x [2 x i32]]* %g4d1_1, i32 0, i32 0, i32 1
   %g2d1_0 = getelementptr inbounds [2 x [2 x i32]], [2 x [2 x i32]]* %g4d1_1, i32 0, i32 1, i32 0