From 665c2e91e29ddfc2a60746d7d2e6bc60fe5d3e08 Mon Sep 17 00:00:00 2001
From: Sairudra More <sairudra60@gmail.com>
Date: Wed, 25 Mar 2026 10:23:52 +0530
Subject: [PATCH] [Flang][OpenMP] Remove dead restoreIP in OpenMP taskloop
 lowering (#187222)

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 000000000000..9397b98b9ecd
--- /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 d14959379526..9193bf5a0c85 100644
--- a/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
+++ b/llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
@@ -2190,7 +2190,6 @@ 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");
@@ -2198,7 +2197,6 @@ 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 000000000000..41121705aa2c
--- /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(