[flang-commits] [flang] [llvm] [mlir] [Flang][OpenMP] Remove dead restoreIP in OpenMP taskloop lowering (PR #187222)

[Sairudra More via flang-commits]

https://github.com/Saieiei updated https://github.com/llvm/llvm-project/pull/187222

>From d166eb157537bfa9d99e531ea435d50c0269f509 Mon Sep 17 00:00:00 2001
From: Saieiei <sairudra60 at gmail.com>
Date: Wed, 18 Mar 2026 04:23:39 -0500
Subject: [PATCH] [flang] Remove dead restoreIP in OpenMP taskloop lowering

This fixes an intermittent crash in OpenMP taskloop lowering.

In OMPIRBuilder::createTaskloop, the restoreIP in PostOutlineCB was immediately overwritten by the following Builder.SetInsertPoint(StaleCI) with no instructions created in between, so it was effectively dead. This patch removes that dead restore, which is the smallest change and preserves the intended IR placement.

Adds a regression test that compiles a taskloop to LLVM IR and verifies
the bounds casts and __kmpc_taskloop call are present.
---
 .../OpenMP/taskloop-bounds-cast.f90           | 33 +++++++++++++++++++
 llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp     |  2 --
 .../LLVMIR/openmp-taskloop-bounds-cast.mlir   | 27 +++++++++++++++
 3 files changed, 60 insertions(+), 2 deletions(-)
 create mode 100644 flang/test/Integration/OpenMP/taskloop-bounds-cast.f90
 create mode 100644 mlir/test/Target/LLVMIR/openmp-taskloop-bounds-cast.mlir

diff --git a/flang/test/Integration/OpenMP/taskloop-bounds-cast.f90 b/flang/test/Integration/OpenMP/taskloop-bounds-cast.f90
new file mode 100644
index 0000000000000..9397b98b9ecd6
--- /dev/null
+++ b/flang/test/Integration/OpenMP/taskloop-bounds-cast.f90
@@ -0,0 +1,33 @@
+!===----------------------------------------------------------------------===!
+! This directory can be used to add Integration tests involving multiple
+! stages of the compiler (for eg. from Fortran to LLVM IR). It should not
+! contain executable tests. We should only add tests here sparingly and only
+! if there is no other way to test. Repeat this message in each test that is
+! added to this directory and sub-directories.
+!===----------------------------------------------------------------------===!
+
+! Regression test for an intermittent crash in taskloop LLVM IR codegen.
+! A dead saveIP/restoreIP pair in OpenMPIRBuilder::createTaskloop introduced
+! stale IRBuilder/debug-location state on the restore path before an
+! immediately following SetInsertPoint override. Removing the dead restore
+! avoids that restore path entirely.
+
+! RUN: %flang_fc1 -emit-llvm -fopenmp -o - %s | FileCheck %s
+
+! Verify that the taskloop runtime call is present in the generated LLVM IR
+! and that the i64 bounds casts required by the ABI are emitted.
+
+! CHECK-LABEL: define void @test_taskloop_(
+
+! CHECK: sext i32 {{.*}} to i64
+! CHECK: call void @__kmpc_taskloop(
+
+subroutine test_taskloop(n)
+  integer, intent(in) :: n
+  integer :: i
+
+  !$omp taskloop
+  do i = 1, n
+  end do
+  !$omp end taskloop
+end subroutine test_taskloop
diff --git a/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp b/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
index 2a0a017fbb0f3..2e73c1791992f 100644
--- a/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
+++ b/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
@@ -2185,7 +2185,6 @@ OpenMPIRBuilder::InsertPointOrErrorTy OpenMPIRBuilder::createTaskloop(
     /* Create the casting for the Bounds Values that can be used when outlining
      * to replace the uses of the fakes with real values */
     BasicBlock *CodeReplBB = StaleCI->getParent();
-    IRBuilderBase::InsertPoint CurrentIp = Builder.saveIP();
     Builder.SetInsertPoint(CodeReplBB->getFirstInsertionPt());
     Value *CastedLBVal =
         Builder.CreateIntCast(LBVal, Builder.getInt64Ty(), true, "lb64");
@@ -2193,7 +2192,6 @@ OpenMPIRBuilder::InsertPointOrErrorTy OpenMPIRBuilder::createTaskloop(
         Builder.CreateIntCast(UBVal, Builder.getInt64Ty(), true, "ub64");
     Value *CastedStepVal =
         Builder.CreateIntCast(StepVal, Builder.getInt64Ty(), true, "step64");
-    Builder.restoreIP(CurrentIp);
 
     Builder.SetInsertPoint(StaleCI);
 
diff --git a/mlir/test/Target/LLVMIR/openmp-taskloop-bounds-cast.mlir b/mlir/test/Target/LLVMIR/openmp-taskloop-bounds-cast.mlir
new file mode 100644
index 0000000000000..41121705aa2c1
--- /dev/null
+++ b/mlir/test/Target/LLVMIR/openmp-taskloop-bounds-cast.mlir
@@ -0,0 +1,27 @@
+// RUN: mlir-translate -mlir-to-llvmir %s | FileCheck %s
+
+// Regression test: a dead saveIP/restoreIP pair in
+// OpenMPIRBuilder::createTaskloop PostOutlineCB could introduce stale
+// IRBuilder debug-location state and cause an intermittent crash during
+// finalize(). Removing the dead pair avoids that restore path entirely.
+// Verifies that an i32 loop is lowered correctly with a __kmpc_taskloop call.
+
+omp.private {type = private} @_QPtest_taskloop_boundsEi_private_i32 : i32
+
+llvm.func @_QPtest_taskloop_bounds() {
+  %0 = llvm.mlir.constant(1 : i64) : i64
+  %1 = llvm.alloca %0 x i32 {bindc_name = "i"} : (i64) -> !llvm.ptr
+  %lb = llvm.mlir.constant(1 : i32) : i32
+  %ub = llvm.mlir.constant(10 : i32) : i32
+  %step = llvm.mlir.constant(1 : i32) : i32
+  omp.taskloop private(@_QPtest_taskloop_boundsEi_private_i32 %1 -> %arg0 : !llvm.ptr) {
+    omp.loop_nest (%arg1) : i32 = (%lb) to (%ub) inclusive step (%step) {
+      llvm.store %arg1, %arg0 : i32, !llvm.ptr
+      omp.yield
+    }
+  }
+  llvm.return
+}
+
+// CHECK-LABEL: define void @_QPtest_taskloop_bounds(
+// CHECK:         call void @__kmpc_taskloop(