[Flang] Add FIR and LLVM lowering support for prefetch directive

* Add PrefetchOp in FirOps
* Handle PrefetchOp in FIR Lowering and also pass required
default values
* Handle PrefetchOp in CodeGen.cpp
* Add required tests

Author: Thirumalai-Shaktivel

flang/include/flang/Optimizer/Dialect/FIROps.td

@@ -351,6 +351,36 @@ def fir_StoreOp : fir_Op<"store", [FirAliasTagOpInterface,
   }];
 }
 
+def fir_PrefetchOp : fir_Op<"prefetch", []> {
+  let summary = "prefetch a memory reference";
+
+  let description = [{
+    The prefetch is a hint to the code generator that the memory reference will
+    be used in the near future. The prefetch is not guaranteed to be executed.
+
+    ```
+      %a = ... -> !fir.ref<i32>
+      fir.prefetch %a {cacheType = 1 : i32, localityHint = 3 : i32, rw = 0 : i32} : !fir.ref<i32>
+      // ...
+      fir.load %a : !fir.ref<i32> // use the prefetched value
+    ```
+  }];
+
+  /// `memref' is the address to be prefetched
+  /// `rw'          : rw specifier >
+  ///                  read is 0, write is 1
+  /// `localityHint': temporal locality specifier >
+  ///                  value ranging from 0 - no locality to 3 - extremely local
+  /// `cacheType'   : cache type specifier >
+  ///                  instruction cache is 0, data cache is 1
+  let arguments = (ins AnyReferenceLike:$memref,
+      ConfinedAttr<I32Attr, [IntMinValue<0>, IntMaxValue<1>]>:$rw,
+      ConfinedAttr<I32Attr, [IntMinValue<0>, IntMaxValue<3>]>:$localityHint,
+      ConfinedAttr<I32Attr, [IntMinValue<0>, IntMaxValue<1>]>:$cacheType);
+
+  let assemblyFormat = "$memref attr-dict `:` type(operands)";
+}
+
 def fir_CopyOp : fir_Op<"copy", [DeclareOpInterfaceMethods<MemoryEffectsOpInterface>]> {
   let summary = "copy constant size memory";
 

flang/lib/Lower/Bridge.cpp

@@ -3276,7 +3276,24 @@ class FirConverter : public Fortran::lower::AbstractConverter {
               attachInliningDirectiveToStmt(dir, &eval);
             },
             [&](const Fortran::parser::CompilerDirective::Prefetch &prefetch) {
-              TODO(getCurrentLocation(), "!$dir prefetch");
+              for (const auto &p : prefetch.v) {
+                Fortran::evaluate::ExpressionAnalyzer ea{
+                    bridge.getSemanticsContext()};
+                Fortran::lower::SomeExpr expr{*ea.Analyze(
+                    std::get<Fortran::parser::DataRef>(p.value().u))};
+                Fortran::lower::StatementContext stmtCtx;
+                mlir::Value memRef{Fortran::lower::convertExprToHLFIR(
+                                       genLocation(dir.source), *this, expr,
+                                       localSymbols, stmtCtx)
+                                       .getBase()};
+
+                // TODO: Don't use default value, instead get the following
+                //       info from the directive
+                uint32_t isWrite{0}, localityHint{3}, isData{1};
+                builder->create<fir::PrefetchOp>(genLocation(dir.source),
+                                                 memRef, isWrite, localityHint,
+                                                 isData);
+              }
             },
             [&](const auto &) {}},
         dir.u);

flang/lib/Optimizer/CodeGen/CodeGen.cpp

@@ -3346,6 +3346,25 @@ struct GlobalOpConversion : public fir::FIROpConversion<fir::GlobalOp> {
   }
 };
 
+/// `fir.prefetch` --> `llvm.prefetch`
+struct PrefetchOpConversion : public fir::FIROpConversion<fir::PrefetchOp> {
+  using FIROpConversion::FIROpConversion;
+
+  llvm::LogicalResult
+  matchAndRewrite(fir::PrefetchOp prefetch, OpAdaptor adaptor,
+                  mlir::ConversionPatternRewriter &rewriter) const override {
+    llvm::errs() << "prefetch\n";
+    mlir::IntegerAttr rw = prefetch.getRwAttr();
+    mlir::IntegerAttr localityHint = prefetch.getLocalityHintAttr();
+    mlir::IntegerAttr cacheType = prefetch.getCacheTypeAttr();
+    mlir::LLVM::Prefetch::create(rewriter, prefetch.getLoc(),
+                                 adaptor.getOperands().front(), rw,
+                                 localityHint, cacheType);
+    rewriter.eraseOp(prefetch);
+    return mlir::success();
+  }
+};
+
 /// `fir.load` --> `llvm.load`
 struct LoadOpConversion : public fir::FIROpConversion<fir::LoadOp> {
   using FIROpConversion::FIROpConversion;
@@ -4423,14 +4442,15 @@ void fir::populateFIRToLLVMConversionPatterns(
       FirEndOpConversion, FreeMemOpConversion, GlobalLenOpConversion,
       GlobalOpConversion, InsertOnRangeOpConversion, IsPresentOpConversion,
       LenParamIndexOpConversion, LoadOpConversion, MulcOpConversion,
-      NegcOpConversion, NoReassocOpConversion, SelectCaseOpConversion,
-      SelectOpConversion, SelectRankOpConversion, SelectTypeOpConversion,
-      ShapeOpConversion, ShapeShiftOpConversion, ShiftOpConversion,
-      SliceOpConversion, StoreOpConversion, StringLitOpConversion,
-      SubcOpConversion, TypeDescOpConversion, TypeInfoOpConversion,
-      UnboxCharOpConversion, UnboxProcOpConversion, UndefOpConversion,
-      UnreachableOpConversion, XArrayCoorOpConversion, XEmboxOpConversion,
-      XReboxOpConversion, ZeroOpConversion>(converter, options);
+      NegcOpConversion, NoReassocOpConversion, PrefetchOpConversion,
+      SelectCaseOpConversion, SelectOpConversion, SelectRankOpConversion,
+      SelectTypeOpConversion, ShapeOpConversion, ShapeShiftOpConversion,
+      ShiftOpConversion, SliceOpConversion, StoreOpConversion,
+      StringLitOpConversion, SubcOpConversion, TypeDescOpConversion,
+      TypeInfoOpConversion, UnboxCharOpConversion, UnboxProcOpConversion,
+      UndefOpConversion, UnreachableOpConversion, XArrayCoorOpConversion,
+      XEmboxOpConversion, XReboxOpConversion, ZeroOpConversion>(converter,
+                                                                options);
 
   // Patterns that are populated without a type converter do not trigger
   // target materializations for the operands of the root op.

flang/test/Integration/prefetch.f90

@@ -0,0 +1,39 @@
+!===----------------------------------------------------------------------===!
+! This directory can be used to add Integration tests involving multiple
+! stages of the compiler (for eg. from Fortran to LLVM IR). It should not
+! contain executable tests. We should only add tests here sparingly and only
+! if there is no other way to test. Repeat this message in each test that is
+! added to this directory and sub-directories.
+!===----------------------------------------------------------------------===!
+
+! RUN: %flang_fc1 -emit-llvm -o - %s | FileCheck %s --check-prefixes=LLVM
+
+!===============================================================================
+! Test lowering of prefetch directive
+!===============================================================================
+
+subroutine test_prefetch_01()
+    ! LLVM: {{.*}} = alloca i32, i64 1, align 4
+    ! LLVM: %[[L_J:.*]] = alloca i32, i64 1, align 4
+    ! LLVM: %[[L_I:.*]] = alloca i32, i64 1, align 4
+    ! LLVM: %[[L_A:.*]] = alloca [256 x i32], i64 1, align 4
+
+    integer :: i, j
+    integer :: a(256)
+
+    a = 23
+    ! LLVM: call void @llvm.prefetch.p0(ptr %6, i32 0, i32 3, i32 1)
+    !dir$ prefetch a
+    i = sum(a)
+    ! LLVM: %[[L_LOAD:.*]] = load i32, ptr %5, align 4
+    ! LLVM: %[[L_ADD:.*]] = add nsw i32 %[[L_LOAD]], 64
+    ! LLVM: %[[L_GEP:.*]] = getelementptr i32, ptr %[[L_A]], i64 {{.*}}
+
+    ! LLVM: call void @llvm.prefetch.p0(ptr %[[L_GEP]], i32 0, i32 3, i32 1)
+    ! LLVM: call void @llvm.prefetch.p0(ptr %[[L_J]], i32 0, i32 3, i32 1)
+
+    do i = 1, (256 - 64)
+      !dir$ prefetch a(i+64), j
+      a(i) = a(i-32) + a(i+32) + j
+    end do
+end subroutine test_prefetch_01

flang/test/Lower/HLFIR/prefetch.f90

@@ -0,0 +1,63 @@
+! Test lowering of prefetch directive
+! RUN: %flang_fc1 -emit-hlfir -o - %s | FileCheck %s --check-prefixes=HLFIR
+
+module test_prefetch_mod
+  implicit none
+  type :: t
+    integer :: a(256, 256)
+  end type t
+end module test_prefetch_mod
+
+subroutine test_prefetch_01()
+  ! HLFIR: %[[H_A:.*]]:2 = hlfir.declare {{.*}} {uniq_name = "_QFtest_prefetch_01Ea"} : (!fir.ref<!fir.array<256xi32>>, !fir.shape<1>) -> (!fir.ref<!fir.array<256xi32>>, !fir.ref<!fir.array<256xi32>>)
+  ! HLFIR: %[[H_I:.*]]:2 = hlfir.declare {{.*}} {uniq_name = "_QFtest_prefetch_01Ei"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+  ! HLFIR: %[[H_J:.*]]:2 = hlfir.declare {{.*}} {uniq_name = "_QFtest_prefetch_01Ej"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+
+  integer :: i, j
+  integer :: a(256)
+
+  a = 23
+
+  ! HLFIR: fir.prefetch %[[H_A]]#0 {cacheType = 1 : i32, localityHint = 3 : i32, rw = 0 : i32} : !fir.ref<!fir.array<256xi32>>
+  !dir$ prefetch a
+  i = sum(a)
+
+  ! HLFIR: %[[H_LOAD:.*]] = fir.load %[[H_I]]#0 : !fir.ref<i32>
+  ! HLFIR: %[[H_C64:.*]] = arith.constant 64 : i32
+  ! HLFIR: %[[H_ADD:.*]] = arith.addi %[[H_LOAD]], %[[H_C64]] overflow<nsw> : i32
+  ! HLFIR: %[[H_CON:.*]] = fir.convert %[[H_ADD]] : (i32) -> i64
+  ! HLFIR: %[[H_DESIG:.*]] = hlfir.designate %[[H_A]]#0 (%[[H_CON]])  : (!fir.ref<!fir.array<256xi32>>, i64) -> !fir.ref<i32>
+
+  ! HLFIR: fir.prefetch %[[H_DESIG]] {cacheType = 1 : i32, localityHint = 3 : i32, rw = 0 : i32} : !fir.ref<i32>
+  ! HLFIR: fir.prefetch %[[H_J]]#0 {cacheType = 1 : i32, localityHint = 3 : i32, rw = 0 : i32} : !fir.ref<i32>
+
+  do i = 1, (256 - 64)
+    !dir$ prefetch a(i+64), j
+    a(i) = a(i-32) + a(i+32) + j
+  end do
+end subroutine test_prefetch_01
+
+subroutine test_prefetch_02(t1)
+  use test_prefetch_mod
+  ! HLFIR: %[[H_A:.*]]:2 = hlfir.declare {{.*}} {fortran_attrs = #fir.var_attrs<allocatable>, uniq_name = "_QFtest_prefetch_02Ea"}
+  ! HLFIR: %[[H_ARG0:.*]]:2 = hlfir.declare {{.*}} dummy_scope {{.*}} {fortran_attrs = #fir.var_attrs<intent_inout>, uniq_name = "_QFtest_prefetch_02Et1"}
+  type(t), intent(inout) :: t1
+  integer, allocatable :: a(:, :)
+
+  ! HLFIR: %[[H_DESIG_01:.*]] = hlfir.designate %[[H_ARG0]]#0{"a"}   shape {{.*}}
+  ! HLFIR: fir.prefetch %[[H_DESIG_01]] {cacheType = 1 : i32, localityHint = 3 : i32, rw = 0 : i32} : !fir.ref<!fir.array<256x256xi32>>
+  !dir$ prefetch t1%a
+  a = t1%a ** 2
+
+  do i = 1, 256
+    ! HLFIR: fir.prefetch %[[H_A]]#0 {cacheType = 1 : i32, localityHint = 3 : i32, rw = 0 : i32} : !fir.ref<!fir.box<!fir.heap<!fir.array<?x?xi32>>>>
+    !dir$ prefetch a
+    a(i, :) = a(i, :) + i
+    do j = 1, 256
+      ! HLFIR: %[[H_DESIG_02:.*]] = hlfir.designate %[[H_ARG0]]#0{"a"} {{.*}}
+      ! HLFIR: fir.prefetch %[[H_DESIG_02]] {cacheType = 1 : i32, localityHint = 3 : i32, rw = 0 : i32} : !fir.ref<i32>
+      !dir$ prefetch t1%a(i, j)
+      t1%a(i, j) = (a(i, j) + i*j) / t1%a(i, j)
+    end do
+  end do
+end subroutine test_prefetch_02