[flang-commits] [flang] [Flang] Add FIR and LLVM lowering support for prefetch directive (PR #167272)
Thirumalai Shaktivel via flang-commits
flang-commits at lists.llvm.org
Sun Nov 9 22:23:06 PST 2025
https://github.com/Thirumalai-Shaktivel created https://github.com/llvm/llvm-project/pull/167272
Implementation details:
* Add PrefetchOp in FirOps
* Handle PrefetchOp in FIR Lowering and also pass required default values
* Handle PrefetchOp in CodeGen.cpp
* Add required tests
>From 79adc2b620b6cbecff043a581412eeab3ca4a255 Mon Sep 17 00:00:00 2001
From: Thirumalai-Shaktivel <thirumalaishaktivel at gmail.com>
Date: Mon, 10 Nov 2025 06:11:37 +0000
Subject: [PATCH] [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
---
.../include/flang/Optimizer/Dialect/FIROps.td | 30 +++++++++
flang/lib/Lower/Bridge.cpp | 19 +++++-
flang/lib/Optimizer/CodeGen/CodeGen.cpp | 36 ++++++++---
flang/test/Integration/prefetch.f90 | 39 ++++++++++++
flang/test/Lower/HLFIR/prefetch.f90 | 63 +++++++++++++++++++
5 files changed, 178 insertions(+), 9 deletions(-)
create mode 100644 flang/test/Integration/prefetch.f90
create mode 100644 flang/test/Lower/HLFIR/prefetch.f90
diff --git a/flang/include/flang/Optimizer/Dialect/FIROps.td b/flang/include/flang/Optimizer/Dialect/FIROps.td
index bae52d63fda45..84d7ed29292ae 100644
--- a/flang/include/flang/Optimizer/Dialect/FIROps.td
+++ b/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 = "$memref attr-dict `:` type(operands)";
+}
+
def fir_CopyOp : fir_Op<"copy", [DeclareOpInterfaceMethods<MemoryEffectsOpInterface>]> {
let summary = "copy constant size memory";
diff --git a/flang/lib/Lower/Bridge.cpp b/flang/lib/Lower/Bridge.cpp
index 5779bcd5d293c..9d8e765e8adea 100644
--- a/flang/lib/Lower/Bridge.cpp
+++ b/flang/lib/Lower/Bridge.cpp
@@ -3276,7 +3276,24 @@ class FirConverter : public Fortran::lower::AbstractConverter {
attachInliningDirectiveToStmt(dir, &eval);
},
[&](const Fortran::parser::CompilerDirective::Prefetch &prefetch) {
- TODO(getCurrentLocation(), "!$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);
diff --git a/flang/lib/Optimizer/CodeGen/CodeGen.cpp b/flang/lib/Optimizer/CodeGen/CodeGen.cpp
index ca4aefb653d2a..69734a2ae443d 100644
--- a/flang/lib/Optimizer/CodeGen/CodeGen.cpp
+++ b/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.
diff --git a/flang/test/Integration/prefetch.f90 b/flang/test/Integration/prefetch.f90
new file mode 100644
index 0000000000000..1f7f6d091cfaa
--- /dev/null
+++ b/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
diff --git a/flang/test/Lower/HLFIR/prefetch.f90 b/flang/test/Lower/HLFIR/prefetch.f90
new file mode 100644
index 0000000000000..3fe0a1a18c4c3
--- /dev/null
+++ b/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
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