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[Flang][OpenMP] Remove dead restoreIP in OpenMP taskloop lowering (#187222)

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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.
This commit is contained in:
Sairudra More 2026-03-25 10:23:52 +05:30 committed by GitHub
parent b16e012603
commit 665c2e91e2
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GPG Key ID: B5690EEEBB952194
3 changed files with 60 additions and 2 deletions
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33
flang/test/Integration/OpenMP/taskloop-bounds-cast.f90 Normal file
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@ -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

2
llvm/lib/Frontend/OpenMP/OMPIRBuilder.cpp
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@ -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);

27
mlir/test/Target/LLVMIR/openmp-taskloop-bounds-cast.mlir Normal file
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@ -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(