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

[Sairudra More via flang-commits]

https://github.com/Saieiei created https://github.com/llvm/llvm-project/pull/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.

>From 447ae0de678878cba83401bebfd9d94760e00e8d 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.
---
 .../Lower/OpenMP/taskloop-bounds-cast.f90     | 26 +++++++++++++++++++
 llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp     |  2 --
 2 files changed, 26 insertions(+), 2 deletions(-)
 create mode 100644 flang/test/Lower/OpenMP/taskloop-bounds-cast.f90

diff --git a/flang/test/Lower/OpenMP/taskloop-bounds-cast.f90 b/flang/test/Lower/OpenMP/taskloop-bounds-cast.f90
new file mode 100644
index 0000000000000..9a09188bfaa2f
--- /dev/null
+++ b/flang/test/Lower/OpenMP/taskloop-bounds-cast.f90
@@ -0,0 +1,26 @@
+! Test that taskloop LLVM IR codegen does not crash when generating the
+! bounds casts in the PostOutlineCB.  This is a regression test for a
+! use-after-free triggered by a dead saveIP/restoreIP pair in
+! OpenMPIRBuilder::createTaskloop that manipulated the IRBuilder state
+! unnecessarily before an immediately following SetInsertPoint override.
+
+! RUN: %flang_fc1 -emit-llvm -fopenmp -o /dev/null %s
+! 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);