[llvm-branch-commits] [flang] [flang][OpenMP] Provide reasons for calculated sequence length (PR #187866)
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Sat Mar 21 07:05:04 PDT 2026
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-flang-openmp
Author: Krzysztof Parzyszek (kparzysz)
<details>
<summary>Changes</summary>
If the length was limited by some factor, include the reason for what caused the reduction.
Issue: https://github.com/llvm/llvm-project/issues/185287
---
Full diff: https://github.com/llvm/llvm-project/pull/187866.diff
6 Files Affected:
- (modified) flang/include/flang/Semantics/openmp-utils.h (+5-5)
- (modified) flang/lib/Semantics/check-omp-loop.cpp (+9-7)
- (modified) flang/lib/Semantics/openmp-utils.cpp (+33-22)
- (modified) flang/test/Semantics/OpenMP/fuse1.f90 (+1)
- (modified) flang/test/Semantics/OpenMP/loop-transformation-construct02.f90 (+1)
- (modified) flang/test/Semantics/OpenMP/loop-transformation-construct04.f90 (+2)
``````````diff
diff --git a/flang/include/flang/Semantics/openmp-utils.h b/flang/include/flang/Semantics/openmp-utils.h
index de5f9cc9072a3..7c95edf81ada2 100644
--- a/flang/include/flang/Semantics/openmp-utils.h
+++ b/flang/include/flang/Semantics/openmp-utils.h
@@ -197,8 +197,8 @@ struct LoopSequence {
WithReason<int64_t> perfect;
};
- bool isNest() const { return length_ && *length_ == 1; }
- std::optional<int64_t> length() const { return length_; }
+ bool isNest() const { return length_.value == 1; }
+ const WithReason<int64_t> &length() const { return length_; }
const Depth &depth() const { return depth_; }
const std::vector<LoopSequence> &children() const { return children_; }
@@ -223,8 +223,8 @@ struct LoopSequence {
/// Precalculate length and depth.
void precalculate();
- std::optional<int64_t> calculateLength() const;
- std::optional<int64_t> getNestedLength() const;
+ WithReason<int64_t> calculateLength() const;
+ WithReason<int64_t> getNestedLength() const;
Depth calculateDepths() const;
Depth getNestedDepths() const;
@@ -241,7 +241,7 @@ struct LoopSequence {
/// the number of children because a child may result in a sequence, for
/// example a fuse with a reduced loop range. The length of that sequence
/// adds to the length of the owning LoopSequence.
- std::optional<int64_t> length_;
+ WithReason<int64_t> length_;
/// Precalculated depths. Only meaningful if the sequence is a nest.
Depth depth_;
diff --git a/flang/lib/Semantics/check-omp-loop.cpp b/flang/lib/Semantics/check-omp-loop.cpp
index 36b7b22de67ea..df9797ac8e56a 100644
--- a/flang/lib/Semantics/check-omp-loop.cpp
+++ b/flang/lib/Semantics/check-omp-loop.cpp
@@ -294,26 +294,28 @@ void OmpStructureChecker::CheckNestedConstruct(
// in it.
auto needRange{GetAffectedLoopRangeWithReason(beginSpec, version)};
- if (std::optional<int64_t> numLoops{sequence.length()}) {
- if (*numLoops == 0) {
+ if (auto haveLength{sequence.length()}) {
+ if (*haveLength.value == 0) {
context_.Say(beginSource,
"This construct should contain a DO-loop or a loop-nest-generating OpenMP construct"_err_en_US);
} else {
auto assoc{llvm::omp::getDirectiveAssociation(dir)};
- if (*numLoops > 1 && assoc == llvm::omp::Association::LoopNest) {
- context_.Say(beginSource,
+ if (*haveLength.value > 1 && assoc == llvm::omp::Association::LoopNest) {
+ auto &msg{context_.Say(beginSource,
"This construct applies to a loop nest, but has a loop sequence of "
"length %" PRId64 ""_err_en_US,
- *numLoops);
+ *haveLength.value)};
+ haveLength.reason.AttachTo(msg);
}
if (assoc == llvm::omp::Association::LoopSeq) {
if (auto requiredCount{GetRequiredCount(needRange.value)}) {
- if (*requiredCount > 0 && *numLoops < *requiredCount) {
+ if (*requiredCount > 0 && *haveLength.value < *requiredCount) {
auto &msg{context_.Say(beginSource,
"This construct requires a sequence of %" PRId64
" loops, but the loop sequence has a length of %" PRId64
""_err_en_US,
- *requiredCount, *numLoops)};
+ *requiredCount, *haveLength.value)};
+ haveLength.reason.AttachTo(msg);
needRange.reason.AttachTo(msg);
}
}
diff --git a/flang/lib/Semantics/openmp-utils.cpp b/flang/lib/Semantics/openmp-utils.cpp
index 185673444f0f0..aa3a7d364c62a 100644
--- a/flang/lib/Semantics/openmp-utils.cpp
+++ b/flang/lib/Semantics/openmp-utils.cpp
@@ -1083,24 +1083,27 @@ void LoopSequence::precalculate() {
depth_ = calculateDepths();
}
-std::optional<int64_t> LoopSequence::calculateLength() const {
+WithReason<int64_t> LoopSequence::calculateLength() const {
if (!entry_->owner) {
return getNestedLength();
}
if (parser::Unwrap<parser::DoConstruct>(entry_->owner)) {
- return 1;
+ return WithReason<int64_t>(1);
}
auto &omp{DEREF(parser::Unwrap<parser::OpenMPLoopConstruct>(*entry_->owner))};
const parser::OmpDirectiveSpecification &beginSpec{omp.BeginDir()};
llvm::omp::Directive dir{beginSpec.DirId()};
if (!IsLoopTransforming(dir)) {
- return 0;
+ Reason reason;
+ reason.Say(beginSpec.DirName().source,
+ "This construct does not result in a loop nest or a loop sequence"_because_en_US);
+ return {0, std::move(reason)};
}
// TODO: Handle split, apply.
if (IsFullUnroll(omp)) {
- return std::nullopt;
+ return {};
}
auto nestedLength{getNestedLength()};
@@ -1116,24 +1119,33 @@ std::optional<int64_t> LoopSequence::calculateLength() const {
// !$omp do ! error: this should contain a loop (superfluous)
// !$omp fuse ! error: this should contain a loop
// !$omp end fuse
- if (!nestedLength || *nestedLength == 0) {
- return std::nullopt;
+ if (!nestedLength.value || *nestedLength.value == 0) {
+ return {};
}
auto *clause{
parser::omp::FindClause(beginSpec, llvm::omp::Clause::OMPC_looprange)};
if (!clause) {
- return 1;
+ Reason reason;
+ reason.Say(beginSpec.DirName().source,
+ "%s clause was not specified, all loops in the sequence are fused"_because_en_US,
+ GetUpperName(llvm::omp::Clause::OMPC_looprange, version_));
+ return {1, std::move(reason)};
}
auto *loopRange{parser::Unwrap<parser::OmpLooprangeClause>(*clause)};
std::optional<int64_t> count{GetIntValue(std::get<1>(loopRange->t))};
if (!count || *count <= 0) {
- return std::nullopt;
+ return {};
}
- if (*count <= *nestedLength) {
- return 1 + *nestedLength - *count;
+ if (*count <= *nestedLength.value) {
+ int64_t result{1 + *nestedLength.value - *count};
+ Reason reason;
+ reason.Say(beginSpec.DirName().source,
+ "Out of %" PRId64 " loops, %" PRId64 " were fused"_because_en_US,
+ *nestedLength.value, *count);
+ return {result, std::move(reason)};
}
- return std::nullopt;
+ return {};
}
if (dir == llvm::omp::Directive::OMPD_nothing) {
@@ -1141,16 +1153,16 @@ std::optional<int64_t> LoopSequence::calculateLength() const {
}
// For every other loop construct return 1.
- return 1;
+ return {1, Reason()};
}
-std::optional<int64_t> LoopSequence::getNestedLength() const {
- int64_t sum{0};
+WithReason<int64_t> LoopSequence::getNestedLength() const {
+ WithReason<int64_t> sum(0);
for (auto &seq : children_) {
- if (auto len{seq.length()}) {
- sum += *len;
+ if (const auto &len{seq.length()}) {
+ sum = sum + len;
} else {
- return std::nullopt;
+ return {};
}
}
return sum;
@@ -1160,7 +1172,7 @@ LoopSequence::Depth LoopSequence::calculateDepths() const {
// Get the length of the nested sequence. The invalidIC_ and opaqueIC_
// members do not count canonical loop nests, but there can only be one
// for depth to make sense.
- std::optional<int64_t> length{getNestedLength()};
+ WithReason<int64_t> nestedLength{getNestedLength()};
// Get the depths of the code nested in this sequence (e.g. contained in
// entry_), and use it as the basis for the depths of entry_->owner.
auto [semaDepth, perfDepth]{getNestedDepths()};
@@ -1184,7 +1196,7 @@ LoopSequence::Depth LoopSequence::calculateDepths() const {
source, "This code prevents perfect nesting"_because_en_US);
}
}
- if (length.value_or(0) != 1) {
+ if (nestedLength.value.value_or(0) != 1) {
// This may simply be the bottom of the loop nest. Only emit messages
// if the depths are reset back to 0.
if (entry_->owner) {
@@ -1229,13 +1241,12 @@ LoopSequence::Depth LoopSequence::calculateDepths() const {
beginSpec, llvm::omp::Clause::OMPC_depth)}) {
auto &expr{parser::UnwrapRef<parser::Expr>(clause->u)};
auto value{GetIntValue(expr)};
- auto nestedLength{getNestedLength()};
// The result is a perfect nest only if all loop in the sequence
// are fused.
- if (value && nestedLength) {
+ if (value && nestedLength.value) {
auto range{GetAffectedLoopRangeWithReason(beginSpec, version_)};
if (auto required{GetRequiredCount(range.value)}) {
- if (*required == -1 || *required == *nestedLength) {
+ if (*required == -1 || *required == *nestedLength.value) {
return Depth{value, value};
}
Reason reason(std::move(range.reason));
diff --git a/flang/test/Semantics/OpenMP/fuse1.f90 b/flang/test/Semantics/OpenMP/fuse1.f90
index 4dab01ca3ec26..a7dd7e190c16a 100644
--- a/flang/test/Semantics/OpenMP/fuse1.f90
+++ b/flang/test/Semantics/OpenMP/fuse1.f90
@@ -10,6 +10,7 @@ subroutine f
!ERROR: This construct requires a sequence of 2 loops, but the loop sequence has a length of 1
!BECAUSE: LOOPRANGE clause was specified with a count of 2 starting at loop 1
!$omp fuse looprange(1, 2)
+ !BECAUSE: LOOPRANGE clause was not specified, all loops in the sequence are fused
!$omp fuse
do i = 1, 10
end do
diff --git a/flang/test/Semantics/OpenMP/loop-transformation-construct02.f90 b/flang/test/Semantics/OpenMP/loop-transformation-construct02.f90
index 25247c3896cae..d0169c4b721bf 100644
--- a/flang/test/Semantics/OpenMP/loop-transformation-construct02.f90
+++ b/flang/test/Semantics/OpenMP/loop-transformation-construct02.f90
@@ -82,6 +82,7 @@ subroutine loop_transformation_construct6
!ERROR: This construct applies to a loop nest, but has a loop sequence of length 2
!$omp do
+ !BECAUSE: Out of 2 loops, 1 were fused
!$omp fuse looprange(1,1)
!$omp unroll partial(2)
do x = 1, i
diff --git a/flang/test/Semantics/OpenMP/loop-transformation-construct04.f90 b/flang/test/Semantics/OpenMP/loop-transformation-construct04.f90
index 158b030906e07..c23acc2c4c266 100644
--- a/flang/test/Semantics/OpenMP/loop-transformation-construct04.f90
+++ b/flang/test/Semantics/OpenMP/loop-transformation-construct04.f90
@@ -10,6 +10,7 @@ subroutine loop_transformation_construct3
!ERROR: This construct applies to a loop nest, but has a loop sequence of length 2
!$omp do
+ !BECAUSE: Out of 3 loops, 2 were fused
!$omp fuse looprange(1,2)
do x = 1, i
v(x) = x * 2
@@ -32,6 +33,7 @@ subroutine loop_transformation_construct4
!ERROR: This construct applies to a loop nest, but has a loop sequence of length 2
!$omp tile sizes(2)
+ !BECAUSE: Out of 3 loops, 2 were fused
!$omp fuse looprange(1,2)
do x = 1, i
v(x) = x * 2
``````````
</details>
https://github.com/llvm/llvm-project/pull/187866
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