[MLIR][LLVM][Mem2Reg] Relax type equality requirement for load and st…

…ore (llvm#87637)

This commit relaxes Mem2Reg's type equality requirement for the LLVM
dialect's load and store operations. For now, we only allow loads to be
promoted if the reaching definition can be casted into a value of the
target type.

For stores, the same conversion casting check is applied and we ensure
that their result is properly casted to the type of the memory slot.
This is necessary to satisfy assumptions of the general mem2reg pass, as
it creates block arguments with the types of the memory slot.

This relands llvm#87504

mlir/lib/Dialect/LLVMIR/IR/LLVMMemorySlot.cpp

@@ -122,8 +122,37 @@ bool LLVM::StoreOp::storesTo(const MemorySlot &slot) {
   return getAddr() == slot.ptr;
 }
 
+/// Checks that two types are the same or can be cast into one another.
+static bool areCastCompatible(const DataLayout &layout, Type lhs, Type rhs) {
+  return lhs == rhs || (!isa<LLVM::LLVMStructType, LLVM::LLVMArrayType>(lhs) &&
+                        !isa<LLVM::LLVMStructType, LLVM::LLVMArrayType>(rhs) &&
+                        layout.getTypeSize(lhs) == layout.getTypeSize(rhs));
+}
+
+/// Constructs operations that convert `inputValue` into a new value of type
+/// `targetType`. Assumes that this conversion is possible.
+static Value createConversionSequence(RewriterBase &rewriter, Location loc,
+                                      Value inputValue, Type targetType) {
+  if (inputValue.getType() == targetType)
+    return inputValue;
+
+  if (!isa<LLVM::LLVMPointerType>(targetType) &&
+      !isa<LLVM::LLVMPointerType>(inputValue.getType()))
+    return rewriter.createOrFold<LLVM::BitcastOp>(loc, targetType, inputValue);
+
+  if (!isa<LLVM::LLVMPointerType>(targetType))
+    return rewriter.createOrFold<LLVM::PtrToIntOp>(loc, targetType, inputValue);
+
+  if (!isa<LLVM::LLVMPointerType>(inputValue.getType()))
+    return rewriter.createOrFold<LLVM::IntToPtrOp>(loc, targetType, inputValue);
+
+  return rewriter.createOrFold<LLVM::AddrSpaceCastOp>(loc, targetType,
+                                                      inputValue);
+}
+
 Value LLVM::StoreOp::getStored(const MemorySlot &slot, RewriterBase &rewriter) {
-  return getValue();
+  return createConversionSequence(rewriter, getLoc(), getValue(),
+                                  slot.elemType);
 }
 
 bool LLVM::LoadOp::canUsesBeRemoved(
@@ -138,15 +167,18 @@ bool LLVM::LoadOp::canUsesBeRemoved(
   // be removed (provided it loads the exact stored value and is not
   // volatile).
   return blockingUse == slot.ptr && getAddr() == slot.ptr &&
-         getResult().getType() == slot.elemType && !getVolatile_();
+         areCastCompatible(dataLayout, getResult().getType(), slot.elemType) &&
+         !getVolatile_();
 }
 
 DeletionKind LLVM::LoadOp::removeBlockingUses(
     const MemorySlot &slot, const SmallPtrSetImpl<OpOperand *> &blockingUses,
     RewriterBase &rewriter, Value reachingDefinition) {
   // `canUsesBeRemoved` checked this blocking use must be the loaded slot
   // pointer.
-  rewriter.replaceAllUsesWith(getResult(), reachingDefinition);
+  Value newResult = createConversionSequence(
+      rewriter, getLoc(), reachingDefinition, getResult().getType());
+  rewriter.replaceAllUsesWith(getResult(), newResult);
   return DeletionKind::Delete;
 }
 
@@ -161,7 +193,8 @@ bool LLVM::StoreOp::canUsesBeRemoved(
   // fine, provided we are currently promoting its target value. Don't allow a
   // store OF the slot pointer, only INTO the slot pointer.
   return blockingUse == slot.ptr && getAddr() == slot.ptr &&
-         getValue() != slot.ptr && getValue().getType() == slot.elemType &&
+         getValue() != slot.ptr &&
+         areCastCompatible(dataLayout, slot.elemType, getValue().getType()) &&
          !getVolatile_();
 }
 

mlir/test/Dialect/LLVMIR/mem2reg.mlir

@@ -697,3 +697,250 @@ llvm.func @transitive_reaching_def() -> !llvm.ptr {
   %3 = llvm.load %1 {alignment = 8 : i64} : !llvm.ptr -> !llvm.ptr
   llvm.return %3 : !llvm.ptr
 }
+
+// -----
+
+// CHECK-LABEL: @load_int_from_float
+llvm.func @load_int_from_float() -> i32 {
+  %0 = llvm.mlir.constant(1 : i32) : i32
+  // CHECK-NOT: llvm.alloca
+  %1 = llvm.alloca %0 x f32 {alignment = 4 : i64} : (i32) -> !llvm.ptr
+  %2 = llvm.load %1 {alignment = 4 : i64} : !llvm.ptr -> i32
+  // CHECK: %[[UNDEF:.*]] = llvm.mlir.undef
+  // CHECK: %[[BITCAST:.*]] = llvm.bitcast %[[UNDEF]] : f32 to i32
+  // CHECK: llvm.return %[[BITCAST:.*]]
+  llvm.return %2 : i32
+}
+
+// -----
+
+// CHECK-LABEL: @load_float_from_int
+llvm.func @load_float_from_int() -> f32 {
+  %0 = llvm.mlir.constant(1 : i32) : i32
+  // CHECK-NOT: llvm.alloca
+  %1 = llvm.alloca %0 x i32 {alignment = 4 : i64} : (i32) -> !llvm.ptr
+  %2 = llvm.load %1 {alignment = 4 : i64} : !llvm.ptr -> f32
+  // CHECK: %[[UNDEF:.*]] = llvm.mlir.undef
+  // CHECK: %[[BITCAST:.*]] = llvm.bitcast %[[UNDEF]] : i32 to f32
+  // CHECK: llvm.return %[[BITCAST:.*]]
+  llvm.return %2 : f32
+}
+
+// -----
+
+// CHECK-LABEL: @load_int_from_vector
+llvm.func @load_int_from_vector() -> i32 {
+  %0 = llvm.mlir.constant(1 : i32) : i32
+  // CHECK-NOT: llvm.alloca
+  %1 = llvm.alloca %0 x vector<2xi16> : (i32) -> !llvm.ptr
+  %2 = llvm.load %1 {alignment = 4 : i64} : !llvm.ptr -> i32
+  // CHECK: %[[UNDEF:.*]] = llvm.mlir.undef
+  // CHECK: %[[BITCAST:.*]] = llvm.bitcast %[[UNDEF]] : vector<2xi16> to i32
+  // CHECK: llvm.return %[[BITCAST:.*]]
+  llvm.return %2 : i32
+}
+
+// -----
+
+// LLVM arrays cannot be bitcasted, so the following cannot be promoted.
+
+// CHECK-LABEL: @load_int_from_array
+llvm.func @load_int_from_array() -> i32 {
+  %0 = llvm.mlir.constant(1 : i32) : i32
+  // CHECK: llvm.alloca
+  %1 = llvm.alloca %0 x !llvm.array<2 x i16> : (i32) -> !llvm.ptr
+  %2 = llvm.load %1 {alignment = 4 : i64} : !llvm.ptr -> i32
+  // CHECK-NOT: llvm.bitcast
+  llvm.return %2 : i32
+}
+
+// -----
+
+// CHECK-LABEL: @store_int_to_float
+// CHECK-SAME: %[[ARG:.*]]: i32
+llvm.func @store_int_to_float(%arg: i32) -> i32 {
+  %0 = llvm.mlir.constant(1 : i32) : i32
+  // CHECK-NOT: llvm.alloca
+  %1 = llvm.alloca %0 x f32 {alignment = 4 : i64} : (i32) -> !llvm.ptr
+  llvm.store %arg, %1 {alignment = 4 : i64} : i32, !llvm.ptr
+  %2 = llvm.load %1 {alignment = 4 : i64} : !llvm.ptr -> i32
+  // CHECK: llvm.return %[[ARG]]
+  llvm.return %2 : i32
+}
+
+// -----
+
+// CHECK-LABEL: @store_float_to_int
+// CHECK-SAME: %[[ARG:.*]]: f32
+llvm.func @store_float_to_int(%arg: f32) -> i32 {
+  %0 = llvm.mlir.constant(1 : i32) : i32
+  // CHECK-NOT: llvm.alloca
+  %1 = llvm.alloca %0 x i32 {alignment = 4 : i64} : (i32) -> !llvm.ptr
+  llvm.store %arg, %1 {alignment = 4 : i64} : f32, !llvm.ptr
+  %2 = llvm.load %1 {alignment = 4 : i64} : !llvm.ptr -> i32
+  // CHECK: %[[BITCAST:.*]] = llvm.bitcast %[[ARG]] : f32 to i32
+  // CHECK: llvm.return %[[BITCAST]]
+  llvm.return %2 : i32
+}
+
+// -----
+
+// CHECK-LABEL: @store_int_to_vector
+// CHECK-SAME: %[[ARG:.*]]: i32
+llvm.func @store_int_to_vector(%arg: i32) -> vector<4xi8> {
+  %0 = llvm.mlir.constant(1 : i32) : i32
+  // CHECK-NOT: llvm.alloca
+  %1 = llvm.alloca %0 x vector<2xi16> {alignment = 4 : i64} : (i32) -> !llvm.ptr
+  llvm.store %arg, %1 {alignment = 4 : i64} : i32, !llvm.ptr
+  %2 = llvm.load %1 {alignment = 4 : i64} : !llvm.ptr -> vector<4xi8>
+  // CHECK: %[[BITCAST0:.*]] = llvm.bitcast %[[ARG]] : i32 to vector<2xi16>
+  // CHECK: %[[BITCAST1:.*]] = llvm.bitcast %[[BITCAST0]] : vector<2xi16> to vector<4xi8>
+  // CHECK: llvm.return %[[BITCAST1]]
+  llvm.return %2 : vector<4xi8>
+}
+
+// -----
+
+// CHECK-LABEL: @load_ptr_from_int
+llvm.func @load_ptr_from_int() -> !llvm.ptr {
+  %0 = llvm.mlir.constant(1 : i32) : i32
+  // CHECK-NOT: llvm.alloca
+  %1 = llvm.alloca %0 x i64 {alignment = 4 : i64} : (i32) -> !llvm.ptr
+  %2 = llvm.load %1 {alignment = 4 : i64} : !llvm.ptr -> !llvm.ptr
+  // CHECK: %[[UNDEF:.*]] = llvm.mlir.undef
+  // CHECK: %[[CAST:.*]] = llvm.inttoptr %[[UNDEF]] : i64 to !llvm.ptr
+  // CHECK: llvm.return %[[CAST:.*]]
+  llvm.return %2 : !llvm.ptr
+}
+
+// -----
+
+// CHECK-LABEL: @load_int_from_ptr
+llvm.func @load_int_from_ptr() -> i64 {
+  %0 = llvm.mlir.constant(1 : i32) : i32
+  // CHECK-NOT: llvm.alloca
+  %1 = llvm.alloca %0 x !llvm.ptr {alignment = 4 : i64} : (i32) -> !llvm.ptr
+  %2 = llvm.load %1 {alignment = 4 : i64} : !llvm.ptr -> i64
+  // CHECK: %[[UNDEF:.*]] = llvm.mlir.undef
+  // CHECK: %[[CAST:.*]] = llvm.ptrtoint %[[UNDEF]] : !llvm.ptr to i64
+  // CHECK: llvm.return %[[CAST:.*]]
+  llvm.return %2 : i64
+}
+
+// -----
+
+// CHECK-LABEL: @load_ptr_addrspace_cast
+llvm.func @load_ptr_addrspace_cast() -> !llvm.ptr<2> {
+  %0 = llvm.mlir.constant(1 : i32) : i32
+  // CHECK-NOT: llvm.alloca
+  %1 = llvm.alloca %0 x !llvm.ptr<1> {alignment = 4 : i64} : (i32) -> !llvm.ptr
+  %2 = llvm.load %1 {alignment = 4 : i64} : !llvm.ptr -> !llvm.ptr<2>
+  // CHECK: %[[UNDEF:.*]] = llvm.mlir.undef
+  // CHECK: %[[CAST:.*]] = llvm.addrspacecast %[[UNDEF]] : !llvm.ptr<1> to !llvm.ptr<2>
+  // CHECK: llvm.return %[[CAST:.*]]
+  llvm.return %2 : !llvm.ptr<2>
+}
+
+// -----
+
+// CHECK-LABEL: @stores_with_different_types
+// CHECK-SAME: %[[ARG0:.*]]: i64
+// CHECK-SAME: %[[ARG1:.*]]: f64
+llvm.func @stores_with_different_types(%arg0: i64, %arg1: f64, %cond: i1) -> f64 {
+  %0 = llvm.mlir.constant(1 : i32) : i32
+  // CHECK-NOT: llvm.alloca
+  %1 = llvm.alloca %0 x i64 {alignment = 4 : i64} : (i32) -> !llvm.ptr
+  llvm.cond_br %cond, ^bb1, ^bb2
+^bb1:
+  llvm.store %arg0, %1 {alignment = 4 : i64} : i64, !llvm.ptr
+  // CHECK: llvm.br ^[[BB3:.*]](%[[ARG0]]
+  llvm.br ^bb3
+^bb2:
+  llvm.store %arg1, %1 {alignment = 4 : i64} : f64, !llvm.ptr
+  // CHECK: %[[BITCAST:.*]] = llvm.bitcast %[[ARG1]] : f64 to i64
+  // CHECK: llvm.br ^[[BB3]](%[[BITCAST]]
+  llvm.br ^bb3
+// CHECK: ^[[BB3]](%[[BLOCK_ARG:.*]]: i64)
+^bb3:
+  %2 = llvm.load %1 {alignment = 4 : i64} : !llvm.ptr -> f64
+  // CHECK: %[[BITCAST:.*]] = llvm.bitcast %[[BLOCK_ARG]] : i64 to f64
+  // CHECK: llvm.return %[[BITCAST]]
+  llvm.return %2 : f64
+}
+
+// -----
+
+// Verifies that stores with smaller bitsize inputs are not replaced. A trivial
+// implementation will be incorrect due to endianness considerations.
+
+// CHECK-LABEL: @stores_with_different_type_sizes
+llvm.func @stores_with_different_type_sizes(%arg0: i64, %arg1: f32, %cond: i1) -> f64 {
+  %0 = llvm.mlir.constant(1 : i32) : i32
+  // CHECK: llvm.alloca
+  %1 = llvm.alloca %0 x i64 {alignment = 4 : i64} : (i32) -> !llvm.ptr
+  llvm.cond_br %cond, ^bb1, ^bb2
+^bb1:
+  llvm.store %arg0, %1 {alignment = 4 : i64} : i64, !llvm.ptr
+  llvm.br ^bb3
+^bb2:
+  llvm.store %arg1, %1 {alignment = 4 : i64} : f32, !llvm.ptr
+  llvm.br ^bb3
+^bb3:
+  %2 = llvm.load %1 {alignment = 4 : i64} : !llvm.ptr -> f64
+  llvm.return %2 : f64
+}
+
+// -----
+
+// CHECK-LABEL: @load_smaller_int
+llvm.func @load_smaller_int() -> i16 {
+  %0 = llvm.mlir.constant(1 : i32) : i32
+  // CHECK: llvm.alloca
+  %1 = llvm.alloca %0 x i32 {alignment = 4 : i64} : (i32) -> !llvm.ptr
+  %2 = llvm.load %1 {alignment = 4 : i64} : !llvm.ptr -> i16
+  llvm.return %2 : i16
+}
+
+// -----
+
+// CHECK-LABEL: @load_different_type_smaller
+llvm.func @load_different_type_smaller() -> f32 {
+  %0 = llvm.mlir.constant(1 : i32) : i32
+  // CHECK: llvm.alloca
+  %1 = llvm.alloca %0 x i64 {alignment = 8 : i64} : (i32) -> !llvm.ptr
+  %2 = llvm.load %1 {alignment = 4 : i64} : !llvm.ptr -> f32
+  llvm.return %2 : f32
+}
+
+// -----
+
+// This alloca is too small for the load, still, mem2reg should not touch it.
+
+// CHECK-LABEL: @impossible_load
+llvm.func @impossible_load() -> f64 {
+  %0 = llvm.mlir.constant(1 : i32) : i32
+  // CHECK: llvm.alloca
+  %1 = llvm.alloca %0 x i32 {alignment = 4 : i64} : (i32) -> !llvm.ptr
+  %2 = llvm.load %1 {alignment = 4 : i64} : !llvm.ptr -> f64
+  llvm.return %2 : f64
+}
+
+// -----
+
+// Verifies that mem2reg does not introduce address space casts of pointers
+// with different bitsize.
+
+module attributes { dlti.dl_spec = #dlti.dl_spec<
+  #dlti.dl_entry<!llvm.ptr<1>, dense<[32, 64, 64]> : vector<3xi64>>,
+  #dlti.dl_entry<!llvm.ptr<2>, dense<[64, 64, 64]> : vector<3xi64>>
+>} {
+
+  // CHECK-LABEL: @load_ptr_addrspace_cast_different_size
+  llvm.func @load_ptr_addrspace_cast_different_size() -> !llvm.ptr<2> {
+    %0 = llvm.mlir.constant(1 : i32) : i32
+    // CHECK: llvm.alloca
+    %1 = llvm.alloca %0 x !llvm.ptr<1> {alignment = 4 : i64} : (i32) -> !llvm.ptr
+    %2 = llvm.load %1 {alignment = 4 : i64} : !llvm.ptr -> !llvm.ptr<2>
+    llvm.return %2 : !llvm.ptr<2>
+  }
+}