[mlir][arith] Add overflow flags support to arith ops (#78376)

Add overflow flags support to the following ops:
* `arith.addi`
* `arith.subi`
* `arith.muli`

Example of new syntax:
```
%res = arith.addi %arg1, %arg2 overflow<nsw> : i64
```
Similar to existing LLVM dialect syntax
```
%res = llvm.add %arg1, %arg2 overflow<nsw> : i64
```

Tablegen canonicalization patterns updated to always drop flags, proper
support with tests will be added later.

Updated LLVMIR translation as part of this commit as it currenly written
in a way that it will crash when new attributes added to arith ops
otherwise.

Also lower `arith` overflow flags to corresponding SPIR-V op decorations

Discussion

https://discourse.llvm.org/t/rfc-integer-overflow-flags-support-in-arith-dialect/76025

This effectively rolls forward #77211, #77700 and #77714 while adding a
test to ensure the Python usage is not broken. More follow up needed but
unrelated to the core change here. The changes here are minimal and just
correspond to "textual namespacing" ODS side, no C++ or Python changes
were needed.

---------

---------

Co-authored-by: Ivan Butygin <ivan.butygin@gmail.com>, Yi Wu <yi.wu2@arm.com>

mlir/include/mlir/Conversion/ArithCommon/AttrToLLVMConverter.h

@@ -18,14 +18,24 @@
 
 namespace mlir {
 namespace arith {
-// Map arithmetic fastmath enum values to LLVMIR enum values.
+/// Maps arithmetic fastmath enum values to LLVM enum values.
 LLVM::FastmathFlags
 convertArithFastMathFlagsToLLVM(arith::FastMathFlags arithFMF);
 
-// Create an LLVM fastmath attribute from a given arithmetic fastmath attribute.
+/// Creates an LLVM fastmath attribute from a given arithmetic fastmath
+/// attribute.
 LLVM::FastmathFlagsAttr
 convertArithFastMathAttrToLLVM(arith::FastMathFlagsAttr fmfAttr);
 
+/// Maps arithmetic overflow enum values to LLVM enum values.
+LLVM::IntegerOverflowFlags
+convertArithOverflowFlagsToLLVM(arith::IntegerOverflowFlags arithFlags);
+
+/// Creates an LLVM overflow attribute from a given arithmetic overflow
+/// attribute.
+LLVM::IntegerOverflowFlagsAttr
+convertArithOverflowAttrToLLVM(arith::IntegerOverflowFlagsAttr flagsAttr);
+
 // Attribute converter that populates a NamedAttrList by removing the fastmath
 // attribute from the source operation attributes, and replacing it with an
 // equivalent LLVM fastmath attribute.
@@ -36,19 +46,46 @@ class AttrConvertFastMathToLLVM {
     // Copy the source attributes.
     convertedAttr = NamedAttrList{srcOp->getAttrs()};
     // Get the name of the arith fastmath attribute.
-    llvm::StringRef arithFMFAttrName = SourceOp::getFastMathAttrName();
+    StringRef arithFMFAttrName = SourceOp::getFastMathAttrName();
     // Remove the source fastmath attribute.
-    auto arithFMFAttr = dyn_cast_or_null<arith::FastMathFlagsAttr>(
+    auto arithFMFAttr = dyn_cast_if_present<arith::FastMathFlagsAttr>(
         convertedAttr.erase(arithFMFAttrName));
     if (arithFMFAttr) {
-      llvm::StringRef targetAttrName = TargetOp::getFastmathAttrName();
+      StringRef targetAttrName = TargetOp::getFastmathAttrName();
       convertedAttr.set(targetAttrName,
                         convertArithFastMathAttrToLLVM(arithFMFAttr));
     }
   }
 
   ArrayRef<NamedAttribute> getAttrs() const { return convertedAttr.getAttrs(); }
 
+private:
+  NamedAttrList convertedAttr;
+};
+
+// Attribute converter that populates a NamedAttrList by removing the overflow
+// attribute from the source operation attributes, and replacing it with an
+// equivalent LLVM overflow attribute.
+template <typename SourceOp, typename TargetOp>
+class AttrConvertOverflowToLLVM {
+public:
+  AttrConvertOverflowToLLVM(SourceOp srcOp) {
+    // Copy the source attributes.
+    convertedAttr = NamedAttrList{srcOp->getAttrs()};
+    // Get the name of the arith overflow attribute.
+    StringRef arithAttrName = SourceOp::getIntegerOverflowAttrName();
+    // Remove the source overflow attribute.
+    auto arithAttr = dyn_cast_if_present<arith::IntegerOverflowFlagsAttr>(
+        convertedAttr.erase(arithAttrName));
+    if (arithAttr) {
+      StringRef targetAttrName = TargetOp::getIntegerOverflowAttrName();
+      convertedAttr.set(targetAttrName,
+                        convertArithOverflowAttrToLLVM(arithAttr));
+    }
+  }
+
+  ArrayRef<NamedAttribute> getAttrs() const { return convertedAttr.getAttrs(); }
+
 private:
   NamedAttrList convertedAttr;
 };

mlir/include/mlir/Dialect/Arith/IR/ArithBase.td

@@ -133,4 +133,27 @@ def Arith_FastMathAttr :
   let assemblyFormat = "`<` $value `>`";
 }
 
+//===----------------------------------------------------------------------===//
+// Arith_IntegerOverflowFlags
+//===----------------------------------------------------------------------===//
+
+def Arith_IOFnone : I32BitEnumAttrCaseNone<"none">;
+def Arith_IOFnsw  : I32BitEnumAttrCaseBit<"nsw", 0>;
+def Arith_IOFnuw  : I32BitEnumAttrCaseBit<"nuw", 1>;
+
+def Arith_IntegerOverflowFlags : I32BitEnumAttr<
+    "IntegerOverflowFlags",
+    "Integer overflow arith flags",
+    [Arith_IOFnone, Arith_IOFnsw, Arith_IOFnuw]> {
+  let separator = ", ";
+  let cppNamespace = "::mlir::arith";
+  let genSpecializedAttr = 0;
+  let printBitEnumPrimaryGroups = 1;
+}
+
+def Arith_IntegerOverflowAttr :
+    EnumAttr<Arith_Dialect, Arith_IntegerOverflowFlags, "overflow"> {
+  let assemblyFormat = "`<` $value `>`";
+}
+
 #endif // ARITH_BASE

mlir/include/mlir/Dialect/Arith/IR/ArithOps.td

@@ -137,6 +137,20 @@ class Arith_CompareOpOfAnyRank<string mnemonic, list<Trait> traits = []> :
   let results = (outs BoolLikeOfAnyRank:$result);
 }
 
+class Arith_IntBinaryOpWithOverflowFlags<string mnemonic, list<Trait> traits = []> :
+    Arith_BinaryOp<mnemonic, traits #
+      [Pure, DeclareOpInterfaceMethods<InferIntRangeInterface>,
+       DeclareOpInterfaceMethods<ArithIntegerOverflowFlagsInterface>]>,
+    Arguments<(ins SignlessIntegerLike:$lhs, SignlessIntegerLike:$rhs,
+      DefaultValuedAttr<
+        Arith_IntegerOverflowAttr,
+        "::mlir::arith::IntegerOverflowFlags::none">:$overflowFlags)>,
+    Results<(outs SignlessIntegerLike:$result)> {
+
+  let assemblyFormat = [{ $lhs `,` $rhs (`overflow` `` $overflowFlags^)?
+                          attr-dict `:` type($result) }];
+}
+
 //===----------------------------------------------------------------------===//
 // ConstantOp
 //===----------------------------------------------------------------------===//
@@ -192,7 +206,7 @@ def Arith_ConstantOp : Op<Arith_Dialect, "constant",
 // AddIOp
 //===----------------------------------------------------------------------===//
 
-def Arith_AddIOp : Arith_TotalIntBinaryOp<"addi", [Commutative]> {
+def Arith_AddIOp : Arith_IntBinaryOpWithOverflowFlags<"addi", [Commutative]> {
   let summary = "integer addition operation";
   let description = [{
     Performs N-bit addition on the operands. The operands are interpreted as 
@@ -203,16 +217,23 @@ def Arith_AddIOp : Arith_TotalIntBinaryOp<"addi", [Commutative]> {
 
     The `addi` operation takes two operands and returns one result, each of
     these is required to be the same type. This type may be an integer scalar type, 
-    a vector whose element type is integer, or a tensor of integers. It has no 
-    standard attributes.
+    a vector whose element type is integer, or a tensor of integers.
+
+    This op supports `nuw`/`nsw` overflow flags which stands stand for
+    "No Unsigned Wrap" and "No Signed Wrap", respectively. If the `nuw` and/or
+    `nsw` flags are present, and an unsigned/signed overflow occurs
+    (respectively), the result is poison.
 
     Example:
 
     ```mlir
     // Scalar addition.
     %a = arith.addi %b, %c : i64
 
-    // SIMD vector element-wise addition, e.g. for Intel SSE.
+    // Scalar addition with overflow flags.
+    %a = arith.addi %b, %c overflow<nsw, nuw> : i64
+
+    // SIMD vector element-wise addition.
     %f = arith.addi %g, %h : vector<4xi32>
 
     // Tensor element-wise addition.
@@ -278,21 +299,41 @@ def Arith_AddUIExtendedOp : Arith_Op<"addui_extended", [Pure, Commutative,
 // SubIOp
 //===----------------------------------------------------------------------===//
 
-def Arith_SubIOp : Arith_TotalIntBinaryOp<"subi"> {
+def Arith_SubIOp : Arith_IntBinaryOpWithOverflowFlags<"subi"> {
   let summary = [{
     Integer subtraction operation.
   }];
   let description = [{
-    Performs N-bit subtraction on the operands. The operands are interpreted as unsigned 
-    bitvectors. The result is represented by a bitvector containing the mathematical 
-    value of the subtraction modulo 2^n, where `n` is the bitwidth. Because `arith` 
-    integers use a two's complement representation, this operation is applicable on 
+    Performs N-bit subtraction on the operands. The operands are interpreted as unsigned
+    bitvectors. The result is represented by a bitvector containing the mathematical
+    value of the subtraction modulo 2^n, where `n` is the bitwidth. Because `arith`
+    integers use a two's complement representation, this operation is applicable on
     both signed and unsigned integer operands.
 
     The `subi` operation takes two operands and returns one result, each of
-    these is required to be the same type. This type may be an integer scalar type, 
-    a vector whose element type is integer, or a tensor of integers. It has no 
-    standard attributes.
+    these is required to be the same type. This type may be an integer scalar type,
+    a vector whose element type is integer, or a tensor of integers.
+
+    This op supports `nuw`/`nsw` overflow flags which stands stand for
+    "No Unsigned Wrap" and "No Signed Wrap", respectively. If the `nuw` and/or
+    `nsw` flags are present, and an unsigned/signed overflow occurs
+    (respectively), the result is poison.
+
+    Example:
+
+    ```mlir
+    // Scalar subtraction.
+    %a = arith.subi %b, %c : i64
+
+    // Scalar subtraction with overflow flags.
+    %a = arith.subi %b, %c overflow<nsw, nuw> : i64
+
+    // SIMD vector element-wise subtraction.
+    %f = arith.subi %g, %h : vector<4xi32>
+
+    // Tensor element-wise subtraction.
+    %x = arith.subi %y, %z : tensor<4x?xi8>
+    ```
   }];
   let hasFolder = 1;
   let hasCanonicalizer = 1;
@@ -302,21 +343,41 @@ def Arith_SubIOp : Arith_TotalIntBinaryOp<"subi"> {
 // MulIOp
 //===----------------------------------------------------------------------===//
 
-def Arith_MulIOp : Arith_TotalIntBinaryOp<"muli", [Commutative]> {
+def Arith_MulIOp : Arith_IntBinaryOpWithOverflowFlags<"muli", [Commutative]> {
   let summary = [{
     Integer multiplication operation.
   }];
   let description = [{
-    Performs N-bit multiplication on the operands. The operands are interpreted as 
-    unsigned bitvectors. The result is represented by a bitvector containing the 
-    mathematical value of the multiplication modulo 2^n, where `n` is the bitwidth. 
-    Because `arith` integers use a two's complement representation, this operation is 
+    Performs N-bit multiplication on the operands. The operands are interpreted as
+    unsigned bitvectors. The result is represented by a bitvector containing the
+    mathematical value of the multiplication modulo 2^n, where `n` is the bitwidth.
+    Because `arith` integers use a two's complement representation, this operation is
     applicable on both signed and unsigned integer operands.
 
     The `muli` operation takes two operands and returns one result, each of
-    these is required to be the same type. This type may be an integer scalar type, 
-    a vector whose element type is integer, or a tensor of integers. It has no 
-    standard attributes.    
+    these is required to be the same type. This type may be an integer scalar type,
+    a vector whose element type is integer, or a tensor of integers.
+
+    This op supports `nuw`/`nsw` overflow flags which stands stand for
+    "No Unsigned Wrap" and "No Signed Wrap", respectively. If the `nuw` and/or
+    `nsw` flags are present, and an unsigned/signed overflow occurs
+    (respectively), the result is poison.
+
+    Example:
+
+    ```mlir
+    // Scalar multiplication.
+    %a = arith.muli %b, %c : i64
+
+    // Scalar multiplication with overflow flags.
+    %a = arith.muli %b, %c overflow<nsw, nuw> : i64
+
+    // SIMD vector element-wise multiplication.
+    %f = arith.muli %g, %h : vector<4xi32>
+
+    // Tensor element-wise multiplication.
+    %x = arith.muli %y, %z : tensor<4x?xi8>
+    ```
   }];
   let hasFolder = 1;
   let hasCanonicalizer = 1;

mlir/include/mlir/Dialect/Arith/IR/ArithOpsInterfaces.td

@@ -49,4 +49,61 @@ def ArithFastMathInterface : OpInterface<"ArithFastMathInterface"> {
   ];
 }
 
+def ArithIntegerOverflowFlagsInterface : OpInterface<"ArithIntegerOverflowFlagsInterface"> {
+  let description = [{
+    Access to op integer overflow flags.
+  }];
+
+  let cppNamespace = "::mlir::arith";
+
+  let methods = [
+    InterfaceMethod<
+      /*desc=*/        "Returns an IntegerOverflowFlagsAttr attribute for the operation",
+      /*returnType=*/  "IntegerOverflowFlagsAttr",
+      /*methodName=*/  "getOverflowAttr",
+      /*args=*/        (ins),
+      /*methodBody=*/  [{}],
+      /*defaultImpl=*/ [{
+        auto op = cast<ConcreteOp>(this->getOperation());
+        return op.getOverflowFlagsAttr();
+      }]
+      >,
+    InterfaceMethod<
+      /*desc=*/        "Returns whether the operation has the No Unsigned Wrap keyword",
+      /*returnType=*/  "bool",
+      /*methodName=*/  "hasNoUnsignedWrap",
+      /*args=*/        (ins),
+      /*methodBody=*/  [{}],
+      /*defaultImpl=*/ [{
+        auto op = cast<ConcreteOp>(this->getOperation());
+        IntegerOverflowFlags flags = op.getOverflowFlagsAttr().getValue();
+        return bitEnumContainsAll(flags, IntegerOverflowFlags::nuw);
+      }]
+      >,
+    InterfaceMethod<
+      /*desc=*/        "Returns whether the operation has the No Signed Wrap keyword",
+      /*returnType=*/  "bool",
+      /*methodName=*/  "hasNoSignedWrap",
+      /*args=*/        (ins),
+      /*methodBody=*/  [{}],
+      /*defaultImpl=*/ [{
+        auto op = cast<ConcreteOp>(this->getOperation());
+        IntegerOverflowFlags flags = op.getOverflowFlagsAttr().getValue();
+        return bitEnumContainsAll(flags, IntegerOverflowFlags::nsw);
+      }]
+      >,
+    StaticInterfaceMethod<
+      /*desc=*/        [{Returns the name of the IntegerOverflowFlagsAttr attribute
+                         for the operation}],
+      /*returnType=*/  "StringRef",
+      /*methodName=*/  "getIntegerOverflowAttrName",
+      /*args=*/        (ins),
+      /*methodBody=*/  [{}],
+      /*defaultImpl=*/ [{
+        return "overflowFlags";
+      }]
+      >
+  ];
+}
+
 #endif // ARITH_OPS_INTERFACES

mlir/include/mlir/Dialect/LLVMIR/LLVMInterfaces.td

@@ -92,7 +92,7 @@ def IntegerOverflowFlagsInterface : OpInterface<"IntegerOverflowFlagsInterface">
       }]
       >,
     StaticInterfaceMethod<
-      /*desc=*/        [{Returns the name of the IntegerOveflowFlagsAttr attribute
+      /*desc=*/        [{Returns the name of the IntegerOverflowFlagsAttr attribute
                          for the operation}],
       /*returnType=*/  "StringRef",
       /*methodName=*/  "getIntegerOverflowAttrName",

mlir/lib/Conversion/ArithCommon/AttrToLLVMConverter.cpp

@@ -10,7 +10,6 @@
 
 using namespace mlir;
 
-// Map arithmetic fastmath enum values to LLVMIR enum values.
 LLVM::FastmathFlags
 mlir::arith::convertArithFastMathFlagsToLLVM(arith::FastMathFlags arithFMF) {
   LLVM::FastmathFlags llvmFMF{};
@@ -22,17 +21,37 @@ mlir::arith::convertArithFastMathFlagsToLLVM(arith::FastMathFlags arithFMF) {
       {arith::FastMathFlags::contract, LLVM::FastmathFlags::contract},
       {arith::FastMathFlags::afn, LLVM::FastmathFlags::afn},
       {arith::FastMathFlags::reassoc, LLVM::FastmathFlags::reassoc}};
-  for (auto fmfMap : flags) {
-    if (bitEnumContainsAny(arithFMF, fmfMap.first))
-      llvmFMF = llvmFMF | fmfMap.second;
+  for (auto [arithFlag, llvmFlag] : flags) {
+    if (bitEnumContainsAny(arithFMF, arithFlag))
+      llvmFMF = llvmFMF | llvmFlag;
   }
   return llvmFMF;
 }
 
-// Create an LLVM fastmath attribute from a given arithmetic fastmath attribute.
 LLVM::FastmathFlagsAttr
 mlir::arith::convertArithFastMathAttrToLLVM(arith::FastMathFlagsAttr fmfAttr) {
   arith::FastMathFlags arithFMF = fmfAttr.getValue();
   return LLVM::FastmathFlagsAttr::get(
       fmfAttr.getContext(), convertArithFastMathFlagsToLLVM(arithFMF));
 }
+
+LLVM::IntegerOverflowFlags mlir::arith::convertArithOverflowFlagsToLLVM(
+    arith::IntegerOverflowFlags arithFlags) {
+  LLVM::IntegerOverflowFlags llvmFlags{};
+  const std::pair<arith::IntegerOverflowFlags, LLVM::IntegerOverflowFlags>
+      flags[] = {
+          {arith::IntegerOverflowFlags::nsw, LLVM::IntegerOverflowFlags::nsw},
+          {arith::IntegerOverflowFlags::nuw, LLVM::IntegerOverflowFlags::nuw}};
+  for (auto [arithFlag, llvmFlag] : flags) {
+    if (bitEnumContainsAny(arithFlags, arithFlag))
+      llvmFlags = llvmFlags | llvmFlag;
+  }
+  return llvmFlags;
+}
+
+LLVM::IntegerOverflowFlagsAttr mlir::arith::convertArithOverflowAttrToLLVM(
+    arith::IntegerOverflowFlagsAttr flagsAttr) {
+  arith::IntegerOverflowFlags arithFlags = flagsAttr.getValue();
+  return LLVM::IntegerOverflowFlagsAttr::get(
+      flagsAttr.getContext(), convertArithOverflowFlagsToLLVM(arithFlags));
+}