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[flang] Better IS_CONTIGUOUS folding for substrings (llvm#115970)
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At present, the compiler doesn't analyze substring references for
contiguity. But there are cases where substrings can be known to be
contiguous (scalar base, empty substring, or complete substring) or can
be known to be discontiguous, and references to the intrinsic function
IS_CONTIGUOUS in those cases may appear in constant expressions.

Fixes llvm#115675.
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@klausler @akshayrdeodhar
klausler authored and akshayrdeodhar committed Nov 18, 2024
1 parent 4493d74 commit 55b95e7
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Showing 6 changed files with 77 additions and 11 deletions.
53 changes: 52 additions & 1 deletion flang/lib/Evaluate/check-expression.cpp
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Original file line number Diff line number Diff line change
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:)
}
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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Original file line number Diff line number Diff line change
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
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4 changes: 2 additions & 2 deletions flang/test/Lower/HLFIR/maxloc.f90
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Original file line number Diff line number Diff line change
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
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4 changes: 2 additions & 2 deletions flang/test/Lower/HLFIR/maxval.f90
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Original file line number Diff line number Diff line change
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
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4 changes: 2 additions & 2 deletions flang/test/Lower/HLFIR/minloc.f90
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Original file line number Diff line number Diff line change
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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Original file line number Diff line number Diff line change
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
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