[flang][openacc] Add lowering for max operator

[clementval]

Summary

Add support for the max operator in the reduction
clause.

Depdns on D151671

[razvanlupusoru]

Thank you. The comments I left for "min" apply here also:
https://reviews.llvm.org/D151671

Otherwise, great work!

[jeanPerier]

flang/lib/Lower/OpenACC.cpp

615

I advise using fir::genMax() (https://reviews.llvm.org/D151671).

[clementval]

Use genMax

[jeanPerier]

Patch application issues, but the code looks good

[clementval]

Rebase

[clementval]

clang-format

flang/lib/Lower/OpenACC.cpp

getReductionOperator(const Fortran::parser::AccReductionOperator &op) {
   llvm_unreachable("unexpected reduction operator");
 }
 
 static mlir::Value genReductionInitValue(fir::FirOpBuilder &builder,
                                          mlir::Location loc, mlir::Type ty,
                                          mlir::acc::ReductionOperator op) {
   if (op != mlir::acc::ReductionOperator::AccAdd &&
       op != mlir::acc::ReductionOperator::AccMul &&
-      op != mlir::acc::ReductionOperator::AccMin)
+      op != mlir::acc::ReductionOperator::AccMin &&
+      op != mlir::acc::ReductionOperator::AccMax)
     TODO(loc, "reduction operator");
 
   // min -> largest
   if (op == mlir::acc::ReductionOperator::AccMin) {
     if (ty.isIntOrIndex()) {
       unsigned bits = ty.getIntOrFloatBitWidth();
       return builder.create<mlir::arith::ConstantOp>(
           loc, ty,
           builder.getIntegerAttr(
               ty, llvm::APInt::getSignedMaxValue(bits).getSExtValue()));
     }
     if (auto floatTy = mlir::dyn_cast_or_null<mlir::FloatType>(ty)) {
       const llvm::fltSemantics &sem = floatTy.getFloatSemantics();
       return builder.create<mlir::arith::ConstantOp>(
           loc, ty,
           builder.getFloatAttr(
               ty, llvm::APFloat::getLargest(sem, /*negative=*/false)));
     }
+    // max -> least
+  } else if (op == mlir::acc::ReductionOperator::AccMax) {
+    if (ty.isIntOrIndex())
+      return builder.create<mlir::arith::ConstantOp>(
+          loc, ty,
+          builder.getIntegerAttr(
+              ty, llvm::APInt::getSignedMinValue(ty.getIntOrFloatBitWidth())
+                      .getSExtValue()));
+    if (auto floatTy = mlir::dyn_cast_or_null<mlir::FloatType>(ty))
+      return builder.create<mlir::arith::ConstantOp>(
+          loc, ty,
+          builder.getFloatAttr(
+              ty, llvm::APFloat::getSmallest(floatTy.getFloatSemantics(),
+                                             /*negative=*/true)));
   } else {
     // 0 for +, ior, ieor
     // 1 for *
     int64_t initValue = op == mlir::acc::ReductionOperator::AccMul ? 1 : 0;
     if (ty.isIntOrIndex())
       return builder.create<mlir::arith::ConstantOp>(
           loc, ty, builder.getIntegerAttr(ty, initValue));
     if (mlir::isa<mlir::FloatType>(ty))
       return builder.create<mlir::arith::ConstantOp>(
           loc, ty, builder.getFloatAttr(ty, initValue));
   }
+
   TODO(loc, "reduction type");
 }
 
 static mlir::Value genCombiner(fir::FirOpBuilder &builder, mlir::Location loc,
                                mlir::acc::ReductionOperator op, mlir::Type ty,
                                mlir::Value value1, mlir::Value value2) {
   if (op == mlir::acc::ReductionOperator::AccAdd) {
     if (ty.isIntOrIndex())
if (op == mlir::acc::ReductionOperator::AccMul) {
     if (mlir::isa<mlir::FloatType>(ty))
       return builder.create<mlir::arith::MulFOp>(loc, value1, value2);
     TODO(loc, "reduction mul type");
   }
 
   if (op == mlir::acc::ReductionOperator::AccMin)
     return fir::genMin(builder, loc, {value1, value2});
 
+  if (op == mlir::acc::ReductionOperator::AccMax)
+    return fir::genMax(builder, loc, {value1, value2});
+
   TODO(loc, "reduction operator");
 }
 
 mlir::acc::ReductionRecipeOp Fortran::lower::createOrGetReductionRecipe(
     fir::FirOpBuilder &builder, llvm::StringRef recipeName, mlir::Location loc,
     mlir::Type ty, mlir::acc::ReductionOperator op) {
   mlir::ModuleOp mod =
       builder.getBlock()->getParent()->getParentOfType<mlir::ModuleOp>();
   if (auto recipe = mod.lookupSymbol<mlir::acc::ReductionRecipeOp>(recipeName))
     return recipe;
 
   auto crtPos = builder.saveInsertionPoint();
   mlir::OpBuilder modBuilder(mod.getBodyRegion());
   auto recipe =
       modBuilder.create<mlir::acc::ReductionRecipeOp>(loc, recipeName, ty, op);

flang/test/Lower/OpenACC/acc-reduction.f90

 ! This test checks lowering of OpenACC reduction clause.
 
 ! RUN: bbc -fopenacc -emit-fir %s -o - | FileCheck %s
 
+! CHECK-LABEL: acc.reduction.recipe @reduction_max_f32 : f32 reduction_operator <max> init {
+! CHECK: ^bb0(%{{.*}}: f32):
+! CHECK:   %[[INIT:.*]] = arith.constant -1.401300e-45 : f32
+! CHECK:   acc.yield %[[INIT]] : f32
+! CHECK: } combiner {
+! CHECK: ^bb0(%[[ARG0:.*]]: f32, %[[ARG1:.*]]: f32):
+! CHECK:   %[[CMP:.*]] = arith.cmpf ogt, %[[ARG0]], %[[ARG1]] : f32
+! CHECK:   %[[SELECT:.*]] = arith.select %[[CMP]], %[[ARG0]], %[[ARG1]] : f32
+! CHECK:   acc.yield %[[SELECT]] : f32
+! CHECK: }
+
+! CHECK-LABEL: acc.reduction.recipe @reduction_max_i32 : i32 reduction_operator <max> init {
+! CHECK: ^bb0(%arg0: i32):
+! CHECK:   %[[INIT:.*]] = arith.constant -2147483648 : i32
+! CHECK:   acc.yield %[[INIT]] : i32
+! CHECK: } combiner {
+! CHECK: ^bb0(%[[ARG0:.*]]: i32, %[[ARG1:.*]]: i32):
+! CHECK:   %[[CMP:.*]] = arith.cmpi sgt, %[[ARG0]], %[[ARG1]] : i32
+! CHECK:   %[[SELECT:.*]] = arith.select %[[CMP]], %[[ARG0]], %[[ARG1]] : i32
+! CHECK:   acc.yield %[[SELECT]] : i32
+! CHECK: }
+
 ! CHECK-LABEL: acc.reduction.recipe @reduction_min_f32 : f32 reduction_operator <min> init {
 ! CHECK: ^bb0(%{{.*}}: f32):
 ! CHECK:   %[[INIT:.*]] = arith.constant 3.40282347E+38 : f32
 ! CHECK:   acc.yield %[[INIT]] : f32
 ! CHECK: } combiner {
 ! CHECK: ^bb0(%[[ARG0:.*]]: f32, %[[ARG1:.*]]: f32):
 ! CHECK:   %[[CMP:.*]] = arith.cmpf olt, %[[ARG0]], %[[ARG1]] : f32
 ! CHECK:   %[[SELECT:.*]] = arith.select %[[CMP]], %[[ARG0]], %[[ARG1]] : f32
subroutine acc_reduction_min_float(a, b)
   do i = 1, 100
     b = min(b, a(i))
   end do
 end subroutine
 
 ! CHECK-LABEL: func.func @_QPacc_reduction_min_float(
 ! CHECK-SAME:  %{{.*}}: !fir.ref<!fir.array<100xf32>> {fir.bindc_name = "a"}, %[[B:.*]]: !fir.ref<f32> {fir.bindc_name = "b"})
 ! CHECK:       acc.loop reduction(@reduction_min_f32 -> %[[B]] : !fir.ref<f32>)
+
+subroutine acc_reduction_max_int(a, b)
+  integer :: a(100)
+  integer :: i, b
+
+  !$acc loop reduction(max:b)
+  do i = 1, 100
+    b = max(b, a(i))
+  end do
+end subroutine
+
+! CHECK-LABEL: func.func @_QPacc_reduction_max_int(
+! CHECK-SAME:  %{{.*}}: !fir.ref<!fir.array<100xi32>> {fir.bindc_name = "a"}, %[[B:.*]]: !fir.ref<i32> {fir.bindc_name = "b"})
+! CHECK:       acc.loop reduction(@reduction_max_i32 -> %[[B]] : !fir.ref<i32>)
+
+subroutine acc_reduction_max_float(a, b)
+  real :: a(100), b
+  integer :: i
+
+  !$acc loop reduction(max:b)
+  do i = 1, 100
+    b = max(b, a(i))
+  end do
+end subroutine
+
+! CHECK-LABEL: func.func @_QPacc_reduction_max_float(
+! CHECK-SAME:  %{{.*}}: !fir.ref<!fir.array<100xf32>> {fir.bindc_name = "a"}, %[[B:.*]]: !fir.ref<f32> {fir.bindc_name = "b"})
+! CHECK:       acc.loop reduction(@reduction_max_f32 -> %[[B]] : !fir.ref<f32>)