[flang-commits] [flang] [Flang] Fix perfect loop nest detection (PR #161554)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-flang-fir-hlfir

Author: Michael Kruse (Meinersbur)

<details>
<summary>Changes</summary>

PR #<!-- -->160283 uses `Unwrap` to detect a `continue` statement, but it applied it on the loop body itelf which sometimes finds a trailing continue statement, but not always. Apply  `Unwrap` on the last body statement instead, where the `continue` is expected.

Fixes #<!-- -->161529

---
Full diff: https://github.com/llvm/llvm-project/pull/161554.diff


4 Files Affected:

- (modified) flang/lib/Semantics/resolve-directives.cpp (+8-5) 
- (added) flang/test/Lower/OpenMP/wsloop-collapse-continue.f90 (+19) 
- (modified) flang/test/Semantics/OpenMP/do08.f90 (-1) 
- (modified) flang/test/Semantics/OpenMP/do13.f90 (-1) 


``````````diff
diff --git a/flang/lib/Semantics/resolve-directives.cpp b/flang/lib/Semantics/resolve-directives.cpp
index bd7b8ac552fab..d32fa3eedae21 100644
--- a/flang/lib/Semantics/resolve-directives.cpp
+++ b/flang/lib/Semantics/resolve-directives.cpp
@@ -2303,14 +2303,17 @@ void OmpAttributeVisitor::CheckPerfectNestAndRectangularLoop(
     }
 
     auto checkPerfectNest = [&, this]() {
-      auto blockSize = block.size();
-      if (blockSize <= 1)
+      if (block.empty())
         return;
+      auto last = block.end();
+      --last;
 
-      if (parser::Unwrap<parser::ContinueStmt>(x))
-        blockSize -= 1;
+      // A trailing CONTINUE or CYCLE does not belong to the loop body
+      if (parser::Unwrap<parser::ContinueStmt>(*last))
+        --last;
 
-      if (blockSize <= 1)
+      // In a perfectly nested loop, the nested loop must be the only statement
+      if (last == block.begin())
         return;
 
       // Non-perfectly nested loop
diff --git a/flang/test/Lower/OpenMP/wsloop-collapse-continue.f90 b/flang/test/Lower/OpenMP/wsloop-collapse-continue.f90
new file mode 100644
index 0000000000000..fea7a8b335d63
--- /dev/null
+++ b/flang/test/Lower/OpenMP/wsloop-collapse-continue.f90
@@ -0,0 +1,19 @@
+! RUN: bbc -fopenmp -emit-hlfir %s -o - | FileCheck %s
+
+program wsloop_collapse_continue
+  integer i, j
+
+! CHECK: omp.wsloop {{.*}} {
+! CHECK: omp.loop_nest ({{.*}}) : i32 = ({{.*}}) to ({{.*}}) inclusive step ({{.*}}) collapse(2) {
+  !$omp do collapse(2)
+  do 50 i = 1, 42
+     do 51 j = 1, 84
+! CHECK: fir.call @_FortranAioOutputInteger32(
+        print *, i
+! CHECK: fir.call @_FortranAioOutputInteger32(
+        print *, j
+     51 continue
+  50 continue
+  !$omp end do
+
+end program wsloop_collapse_continue
diff --git a/flang/test/Semantics/OpenMP/do08.f90 b/flang/test/Semantics/OpenMP/do08.f90
index bb3c1d0cd3855..5143dff0dd315 100644
--- a/flang/test/Semantics/OpenMP/do08.f90
+++ b/flang/test/Semantics/OpenMP/do08.f90
@@ -61,7 +61,6 @@ program omp
   !$omp end do
 
 
-  !ERROR: Canonical loop nest must be perfectly nested.
   !ERROR: The value of the parameter in the COLLAPSE or ORDERED clause must not be larger than the number of nested loops following the construct.
   !$omp do collapse(3)
   do 60 i=2,200,2
diff --git a/flang/test/Semantics/OpenMP/do13.f90 b/flang/test/Semantics/OpenMP/do13.f90
index 8f7844f4136f9..6e9d1dddade4c 100644
--- a/flang/test/Semantics/OpenMP/do13.f90
+++ b/flang/test/Semantics/OpenMP/do13.f90
@@ -59,7 +59,6 @@ program omp
   !$omp end do
 
 
-  !ERROR: Canonical loop nest must be perfectly nested.
   !ERROR: The value of the parameter in the COLLAPSE or ORDERED clause must not be larger than the number of nested loops following the construct.
   !$omp do collapse(3)
   do 60 i=1,10

``````````

</details>


https://github.com/llvm/llvm-project/pull/161554