[flang][hlfir] allow recursive intrinsic lowering

[tblah]

Summary

We need to allow recursive application of intrinsic lowering patterns,
otherwise we cannot lower nested calls of the same intrinsic e.g.
matmul(matmul(a, b), c).

matmul(matmul(a, b), matmul(c, d)) requires hlfir.associate of hlfir
expr with more than one use (TODO).

[vzakhari]

LGTM, though, clang-format is needed.

[tblah]

Thanks for taking a look. Updating with correct formatting.

[tblah]

Reverted because it broke compilation with MSVC

flang/lib/Optimizer/HLFIR/Transforms/LowerHLFIRIntrinsics.cpp

-//===- LowerHLFIRIntrinsics.cpp - Bufferize HLFIR  ------------------------===//
+//===- LowerHLFIRIntrinsics.cpp - Transformational intrinsics to FIR ------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "flang/Optimizer/Builder/FIRBuilder.h"

 } // namespace hlfir
 
 namespace {
 
 /// Base class for passes converting transformational intrinsic operations into
 /// runtime calls
 template <class OP>
 class HlfirIntrinsicConversion : public mlir::OpRewritePattern<OP> {
-  using mlir::OpRewritePattern<OP>::OpRewritePattern;
+public:
+  explicit HlfirIntrinsicConversion(mlir::MLIRContext *ctx)
+      : mlir::OpRewritePattern<OP>{ctx} {
+    // required for cases where intrinsics are chained together e.g.
+    // matmul(matmul(a, b), c)
+    // because converting the inner operation then invalidates the
+    // outer operation: causing the pattern to apply recursively.
+    //
+    // This is safe because we always progress with each iteration. Circular
+    // applications of operations are not expressible in MLIR because we use
+    // an SSA form and one must become first. E.g.
+    // %a = hlfir.matmul %b %d
+    // %b = hlfir.matmul %a %d
+    // cannot be written.
+    mlir::OpConversionPattern<OP>::setHasBoundedRewriteRecursion(true);
+  }
 
 protected:
   struct IntrinsicArgument {
     mlir::Value val; // allowed to be null if the argument is absent
     mlir::Type desiredType;
   };
 
   /// Lower the arguments to the intrinsic: adding nesecarry boxing and

flang/test/HLFIR/matmul-lowering.fir

 // CHECK-NEXT:    %[[TMP:.*]]:2 = hlfir.declare %[[ADDR]](%[[SHIFT]]) {uniq_name = ".tmp.intrinsic_result"}
 // TODO: add shape information from original intrinsic op
 // CHECK:         %[[TRUE:.*]] = arith.constant true
 // CHECK:         %[[ASEXPR:.*]] = hlfir.as_expr %[[TMP]]#0 move %[[TRUE]] : (!fir.box<!fir.array<?x?xi32>>, i1) -> !hlfir.expr<?x?xi32>
 // CHECK:         hlfir.assign %[[ASEXPR]] to %[[RES_VAR]]#0
 // CHECK:         hlfir.destroy %[[ASEXPR]]
 // CHECK-NEXT:    return
 // CHECK-NEXT:  }
+
+// nested matmuls leading to recursive pattern application
+func.func @_QPtest(%arg0: !fir.ref<!fir.array<3x3xf32>> {fir.bindc_name = "a"}, %arg1: !fir.ref<!fir.array<3x3xf32>> {fir.bindc_name = "b"}, %arg2: !fir.ref<!fir.array<3x3xf32>> {fir.bindc_name = "c"}, %arg3: !fir.ref<!fir.array<3x3xf32>> {fir.bindc_name = "out"}) {
+  %c3 = arith.constant 3 : index
+  %c3_0 = arith.constant 3 : index
+  %0 = fir.shape %c3, %c3_0 : (index, index) -> !fir.shape<2>
+  %1:2 = hlfir.declare %arg0(%0) {uniq_name = "_QFtestEa"} : (!fir.ref<!fir.array<3x3xf32>>, !fir.shape<2>) -> (!fir.ref<!fir.array<3x3xf32>>, !fir.ref<!fir.array<3x3xf32>>)
+  %c3_1 = arith.constant 3 : index
+  %c3_2 = arith.constant 3 : index
+  %2 = fir.shape %c3_1, %c3_2 : (index, index) -> !fir.shape<2>
+  %3:2 = hlfir.declare %arg1(%2) {uniq_name = "_QFtestEb"} : (!fir.ref<!fir.array<3x3xf32>>, !fir.shape<2>) -> (!fir.ref<!fir.array<3x3xf32>>, !fir.ref<!fir.array<3x3xf32>>)
+  %c3_3 = arith.constant 3 : index
+  %c3_4 = arith.constant 3 : index
+  %4 = fir.shape %c3_3, %c3_4 : (index, index) -> !fir.shape<2>
+  %5:2 = hlfir.declare %arg2(%4) {uniq_name = "_QFtestEc"} : (!fir.ref<!fir.array<3x3xf32>>, !fir.shape<2>) -> (!fir.ref<!fir.array<3x3xf32>>, !fir.ref<!fir.array<3x3xf32>>)
+  %c3_5 = arith.constant 3 : index
+  %c3_6 = arith.constant 3 : index
+  %6 = fir.shape %c3_5, %c3_6 : (index, index) -> !fir.shape<2>
+  %7:2 = hlfir.declare %arg3(%6) {uniq_name = "_QFtestEout"} : (!fir.ref<!fir.array<3x3xf32>>, !fir.shape<2>) -> (!fir.ref<!fir.array<3x3xf32>>, !fir.ref<!fir.array<3x3xf32>>)
+  %8 = hlfir.matmul %1#0 %3#0 {fastmath = #arith.fastmath<contract>} : (!fir.ref<!fir.array<3x3xf32>>, !fir.ref<!fir.array<3x3xf32>>) -> !hlfir.expr<3x3xf32>
+  %9 = hlfir.matmul %8 %5#0 {fastmath = #arith.fastmath<contract>} : (!hlfir.expr<3x3xf32>, !fir.ref<!fir.array<3x3xf32>>) -> !hlfir.expr<3x3xf32>
+  hlfir.assign %9 to %7#0 : !hlfir.expr<3x3xf32>, !fir.ref<!fir.array<3x3xf32>>
+  hlfir.destroy %9 : !hlfir.expr<3x3xf32>
+  hlfir.destroy %8 : !hlfir.expr<3x3xf32>
+  return
+}
+// just check that we apply the patterns successfully. The details are checked above
+// CHECK-LABEL: func.func @_QPtest(
+// CHECK:           %arg0: !fir.ref<!fir.array<3x3xf32>> {fir.bindc_name = "a"},
+// CHECK-SAME:      %arg1: !fir.ref<!fir.array<3x3xf32>> {fir.bindc_name = "b"},
+// CHECK-SAME:      %arg2: !fir.ref<!fir.array<3x3xf32>> {fir.bindc_name = "c"},
+// CHECK-SAME:      %arg3: !fir.ref<!fir.array<3x3xf32>> {fir.bindc_name = "out"}) {
+// CHECK:         fir.call @_FortranAMatmul(
+// CHECK;         fir.call @_FortranAMatmul(%40, %41, %42, %43, %c20_i32) : (!fir.ref<!fir.box<none>>, !fir.box<none>, !fir.box<none>, !fir.ref<i8>, i32) -> none
+// CHECK:         return
+// CHECK-NEXT:  }