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[flang] Better IS_CONTIGUOUS folding for substrings #115970

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Nov 14, 2024
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[flang] Better IS_CONTIGUOUS folding for substrings #115970

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53 changes: 52 additions & 1 deletion flang/lib/Evaluate/check-expression.cpp
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Expand Up @@ -908,7 +908,58 @@ class IsContiguousHelper
Result operator()(const ComplexPart &x) const {
return x.complex().Rank() == 0;
}
Result operator()(const Substring &) const { return std::nullopt; }
Result operator()(const Substring &x) const {
if (x.Rank() == 0) {
return true; // scalar substring always contiguous
}
// Substrings with rank must have DataRefs as their parents
const DataRef &parentDataRef{DEREF(x.GetParentIf<DataRef>())};
std::optional<std::int64_t> len;
if (auto lenExpr{parentDataRef.LEN()}) {
len = ToInt64(Fold(context_, std::move(*lenExpr)));
if (len) {
if (*len <= 0) {
return true; // empty substrings
} else if (*len == 1) {
// Substrings can't be incomplete; is base array contiguous?
return (*this)(parentDataRef);
}
}
}
std::optional<std::int64_t> upper;
bool upperIsLen{false};
if (auto upperExpr{x.upper()}) {
upper = ToInt64(Fold(context_, common::Clone(*upperExpr)));
if (upper) {
if (*upper < 1) {
return true; // substring(n:0) empty
}
upperIsLen = len && *upper >= *len;
} else if (const auto *inquiry{
UnwrapConvertedExpr<DescriptorInquiry>(*upperExpr)};
inquiry && inquiry->field() == DescriptorInquiry::Field::Len) {
upperIsLen =
&parentDataRef.GetLastSymbol() == &inquiry->base().GetLastSymbol();
}
} else {
upperIsLen = true; // substring(n:)
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@jeanPerier jeanPerier Nov 14, 2024

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It seems that some previous folding step may already have expended the absent upper into the length, blurring the information here for cases where the length is not a compile time constant:

subroutine test(charr)
  character(*) :: charr(5)
  print *, is_contiguous(charr(:)(1:))
end subroutine

Folds to is_contiguous(charr(::1_8)(1_8:int(charr%len,kind=8))) while it could be folded to true.

However, folding this may not be required by the standard, so this may be fine.

I do not find the standard very clear regarding the appearance of IS_CONTIGUOUS in constant expressions. As I understand it, it falls into the 10.1.12 (6) case since IS_CONTIGUOUS is an inquiry function. I am not sure how to read "a variable whose properties inquired about are not assumed, deferred, or defined by an expression that is not a constant expression" when the "property" is the contiguity.

}
if (auto lower{ToInt64(Fold(context_, x.lower()))}) {
if (*lower == 1 && upperIsLen) {
// known complete substring; is base contiguous?
return (*this)(parentDataRef);
} else if (upper) {
if (*upper < *lower) {
return true; // empty substring(3:2)
} else if (*lower > 1) {
return false; // known incomplete substring
} else if (len && *upper < *len) {
return false; // known incomplete substring
}
}
}
return std::nullopt; // contiguity not known
}

Result operator()(const ProcedureRef &x) const {
if (auto chars{characteristics::Procedure::Characterize(
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19 changes: 17 additions & 2 deletions flang/test/Evaluate/folding09.f90
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Expand Up @@ -5,7 +5,7 @@ module m
real, target :: hosted(2)
integer, parameter :: cst(2,2) = reshape([1, 2, 3, 4], shape(cst))
integer, parameter :: empty_cst(2,0) = reshape([1], shape(empty_cst))
integer :: n
integer :: n, m
logical, parameter :: test_param1 = is_contiguous(cst(:,1))
logical, parameter :: test_param2 = is_contiguous(cst(1,:))
logical, parameter :: test_param3 = is_contiguous(cst(:,n))
Expand All @@ -16,11 +16,15 @@ function f()
real, pointer, contiguous :: f(:)
f => hosted
end function
subroutine test(arr1, arr2, arr3, mat, alloc)
subroutine test(arr1, arr2, arr3, mat, alloc, alch)
real, intent(in) :: arr1(:), arr2(10), mat(10, 10)
real, intent(in), contiguous :: arr3(:)
real, allocatable :: alloc(:)
real :: scalar
character(5) charr(5)
character(1) char1(5)
character(0) char0(5)
character(*) alch(5)
integer(kind=merge(1,-1, is_contiguous(0))) t01
integer(kind=merge(1,-1, is_contiguous(scalar))) t02
integer(kind=merge(1,-1, is_contiguous(scalar + scalar))) t03
Expand All @@ -35,6 +39,17 @@ subroutine test(arr1, arr2, arr3, mat, alloc)
integer(kind=merge(1,-1, .not. is_contiguous(arr3(1:10:2)))) t12
integer(kind=merge(1,-1, is_contiguous(f()))) t13
integer(kind=merge(1,-1, is_contiguous(alloc))) t14
integer(kind=merge(1,-1, is_contiguous(charr(:)(:)))) t15
integer(kind=merge(1,-1, is_contiguous(charr(1)(2:3)))) t16
integer(kind=merge(1,-1, is_contiguous(charr(:)(1:)))) t17
integer(kind=merge(1,-1, is_contiguous(charr(:)(3:2)))) t18
integer(kind=merge(1,-1, is_contiguous(charr(:)(1:5)))) t19
integer(kind=merge(1,-1, .not. is_contiguous(charr(:)(1:4)))) t20
integer(kind=merge(1,-1, is_contiguous(char1(:)(n:m)))) t21
integer(kind=merge(1,-1, .not. is_contiguous(char1(1:5:2)(n:m)))) t22
integer(kind=merge(1,-1, is_contiguous(char0(:)(n:m)))) t23
integer(kind=merge(1,-1, is_contiguous(char0(1:5:2)(n:m)))) t24
integer(kind=merge(1,-1, is_contiguous(alch(:)(:)))) t25
associate (x => arr2)
block
integer(kind=merge(1,-1,is_contiguous(x))) n
Expand Down
4 changes: 2 additions & 2 deletions flang/test/Lower/HLFIR/maxloc.f90
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Expand Up @@ -341,8 +341,8 @@ end subroutine test_unknown_char_len_result
! CHECK-DAG: %[[C1_7:.*]] = arith.constant 1 : index
! CHECK-DAG: %[[C3_8:.*]] = arith.constant 3 : index
! CHECK-DAG: %[[C3_9:.*]] = arith.constant 3 : index
! CHECK-DAG: %[[ARRAY_BOX:.*]] = hlfir.designate %[[ARRAY]]#0 (%[[C1]]:%[[C3_0]]:%[[C1_3]], %[[C1]]:%[[C3_1]]:%[[C1_5]]) substr %[[C1_7]], %[[C3_8]] shape %[[SHAPE]] typeparams %[[C3_9]]
! CHECK: %[[EXPR:.*]] = hlfir.maxloc %[[ARRAY_BOX]] {fastmath = #arith.fastmath<contract>} : (!fir.box<!fir.array<3x3x!fir.char<1,3>>>) -> !hlfir.expr<2xi32>
! CHECK-DAG: %[[ARRAY_REF:.*]] = hlfir.designate %[[ARRAY]]#0 (%[[C1]]:%[[C3_0]]:%[[C1_3]], %[[C1]]:%[[C3_1]]:%[[C1_5]]) substr %[[C1_7]], %[[C3_8]] shape %[[SHAPE]] typeparams %[[C3_9]] : (!fir.ref<!fir.array<3x3x!fir.char<1,3>>>, index, index, index, index, index, index, index, index, !fir.shape<2>, index) -> !fir.ref<!fir.array<3x3x!fir.char<1,3>>>
! CHECK: %[[EXPR:.*]] = hlfir.maxloc %[[ARRAY_REF]] {fastmath = #arith.fastmath<contract>} : (!fir.ref<!fir.array<3x3x!fir.char<1,3>>>) -> !hlfir.expr<2xi32>
! CHECK-NEXT: hlfir.assign %[[EXPR]] to %[[RES]]#0 : !hlfir.expr<2xi32>, !fir.ref<!fir.array<2xi32>>
! CHECK-NEXT: hlfir.destroy %[[EXPR]]
! CHECK-NEXT: return
Expand Down
4 changes: 2 additions & 2 deletions flang/test/Lower/HLFIR/maxval.f90
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Expand Up @@ -254,8 +254,8 @@ end subroutine test_unknown_char_len_result
! CHECK-DAG: %[[C1_7:.*]] = arith.constant 1 : index
! CHECK-DAG: %[[C3_8:.*]] = arith.constant 3 : index
! CHECK-DAG: %[[C3_9:.*]] = arith.constant 3 : index
! CHECK-DAG: %[[ARRAY_BOX:.*]] = hlfir.designate %[[ARRAY]]#0 (%[[C1]]:%[[C3_0]]:%[[C1_3]], %[[C1]]:%[[C3_1]]:%[[C1_5]]) substr %[[C1_7]], %[[C3_8]] shape %[[SHAPE]] typeparams %[[C3_9]]
! CHECK: %[[EXPR:.*]] = hlfir.maxval %[[ARRAY_BOX]] {fastmath = #arith.fastmath<contract>} : (!fir.box<!fir.array<3x3x!fir.char<1,3>>>) -> !hlfir.expr<!fir.char<1,3>>
! CHECK-DAG: %[[ARRAY_REF:.*]] = hlfir.designate %[[ARRAY]]#0 (%[[C1]]:%[[C3_0]]:%[[C1_3]], %[[C1]]:%[[C3_1]]:%[[C1_5]]) substr %[[C1_7]], %[[C3_8]] shape %[[SHAPE]] typeparams %[[C3_9]] : (!fir.ref<!fir.array<3x3x!fir.char<1,3>>>, index, index, index, index, index, index, index, index, !fir.shape<2>, index) -> !fir.ref<!fir.array<3x3x!fir.char<1,3>>>
! CHECK: %[[EXPR:.*]] = hlfir.maxval %[[ARRAY_REF]] {fastmath = #arith.fastmath<contract>} : (!fir.ref<!fir.array<3x3x!fir.char<1,3>>>) -> !hlfir.expr<!fir.char<1,3>>
! CHECK-NEXT: hlfir.assign %[[EXPR]] to %[[RES]]#0 : !hlfir.expr<!fir.char<1,3>>, !fir.ref<!fir.char<1,3>>
! CHECK-NEXT: hlfir.destroy %[[EXPR]]
! CHECK-NEXT: return
Expand Down
4 changes: 2 additions & 2 deletions flang/test/Lower/HLFIR/minloc.f90
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Expand Up @@ -341,8 +341,8 @@ end subroutine test_unknown_char_len_result
! CHECK-DAG: %[[C1_7:.*]] = arith.constant 1 : index
! CHECK-DAG: %[[C3_8:.*]] = arith.constant 3 : index
! CHECK-DAG: %[[C3_9:.*]] = arith.constant 3 : index
! CHECK-DAG: %[[ARRAY_BOX:.*]] = hlfir.designate %[[ARRAY]]#0 (%[[C1]]:%[[C3_0]]:%[[C1_3]], %[[C1]]:%[[C3_1]]:%[[C1_5]]) substr %[[C1_7]], %[[C3_8]] shape %[[SHAPE]] typeparams %[[C3_9]]
! CHECK: %[[EXPR:.*]] = hlfir.minloc %[[ARRAY_BOX]] {fastmath = #arith.fastmath<contract>} : (!fir.box<!fir.array<3x3x!fir.char<1,3>>>) -> !hlfir.expr<2xi32>
! CHECK-DAG: %[[ARRAY_REF:.*]] = hlfir.designate %[[ARRAY]]#0 (%[[C1]]:%[[C3_0]]:%[[C1_3]], %[[C1]]:%[[C3_1]]:%[[C1_5]]) substr %[[C1_7]], %[[C3_8]] shape %[[SHAPE]] typeparams %[[C3_9]] : (!fir.ref<!fir.array<3x3x!fir.char<1,3>>>, index, index, index, index, index, index, index, index, !fir.shape<2>, index) -> !fir.ref<!fir.array<3x3x!fir.char<1,3>>>
! CHECK: %[[EXPR:.*]] = hlfir.minloc %[[ARRAY_REF]] {fastmath = #arith.fastmath<contract>} : (!fir.ref<!fir.array<3x3x!fir.char<1,3>>>) -> !hlfir.expr<2xi32>
! CHECK-NEXT: hlfir.assign %[[EXPR]] to %[[RES]]#0 : !hlfir.expr<2xi32>, !fir.ref<!fir.array<2xi32>>
! CHECK-NEXT: hlfir.destroy %[[EXPR]]
! CHECK-NEXT: return
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4 changes: 2 additions & 2 deletions flang/test/Lower/HLFIR/minval.f90
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Expand Up @@ -254,8 +254,8 @@ end subroutine test_unknown_char_len_result
! CHECK-DAG: %[[C1_7:.*]] = arith.constant 1 : index
! CHECK-DAG: %[[C3_8:.*]] = arith.constant 3 : index
! CHECK-DAG: %[[C3_9:.*]] = arith.constant 3 : index
! CHECK-DAG: %[[ARRAY_BOX:.*]] = hlfir.designate %[[ARRAY]]#0 (%[[C1]]:%[[C3_0]]:%[[C1_3]], %[[C1]]:%[[C3_1]]:%[[C1_5]]) substr %[[C1_7]], %[[C3_8]] shape %[[SHAPE]] typeparams %[[C3_9]]
! CHECK: %[[EXPR:.*]] = hlfir.minval %[[ARRAY_BOX]] {fastmath = #arith.fastmath<contract>} : (!fir.box<!fir.array<3x3x!fir.char<1,3>>>) -> !hlfir.expr<!fir.char<1,3>>
! CHECK-DAG: %[[ARRAY_REF:.*]] = hlfir.designate %[[ARRAY]]#0 (%[[C1]]:%[[C3_0]]:%[[C1_3]], %[[C1]]:%[[C3_1]]:%[[C1_5]]) substr %[[C1_7]], %[[C3_8]] shape %[[SHAPE]] typeparams %[[C3_9]] : (!fir.ref<!fir.array<3x3x!fir.char<1,3>>>, index, index, index, index, index, index, index, index, !fir.shape<2>, index) -> !fir.ref<!fir.array<3x3x!fir.char<1,3>>>
! CHECK: %[[EXPR:.*]] = hlfir.minval %[[ARRAY_REF]] {fastmath = #arith.fastmath<contract>} : (!fir.ref<!fir.array<3x3x!fir.char<1,3>>>) -> !hlfir.expr<!fir.char<1,3>>
! CHECK-NEXT: hlfir.assign %[[EXPR]] to %[[RES]]#0 : !hlfir.expr<!fir.char<1,3>>, !fir.ref<!fir.char<1,3>>
! CHECK-NEXT: hlfir.destroy %[[EXPR]]
! CHECK-NEXT: return
Expand Down
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