[Flang]Fix for changed code at the end of AllocaIP. (#92430)

Some of the OpenMP code can change the instruction pointed at by the
insertion point. This leads to an assert in the compiler about
BB->getParent() and IP->getParent() not matching.

The fix is to rebuild the insertionpoint from the block, rather than use
builder.restoreIP.

Also, move some of the alloca generation, rather than skipping back and
forth between insert points (and ensure all the allocas are done before
their users are created).

A simple test, mainly to ensure the minimal reproducer doesn't fail to
compile in the future is also added.

3 files changed, 32 insertions, 17 deletions

diff --git a/mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp b/mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp
index b7b2f8c..cbfc649 100644
--- a/mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp
+++ b/mlir/lib/Target/LLVMIR/Dialect/OpenMP/OpenMPToLLVMIRTranslation.cpp
@@ -770,7 +770,7 @@ static void allocByValReductionVars(
     DenseMap<Value, llvm::Value *> &reductionVariableMap,
     llvm::ArrayRef<bool> isByRefs) {
   llvm::IRBuilderBase::InsertPointGuard guard(builder);
-  builder.restoreIP(allocaIP);
+  builder.SetInsertPoint(allocaIP.getBlock()->getTerminator());
   auto args =
       loop.getRegion().getArguments().take_back(loop.getNumReductionVars());
 
@@ -780,7 +780,7 @@ static void allocByValReductionVars(
     llvm::Value *var = builder.CreateAlloca(
         moduleTranslation.convertType(reductionDecls[i].getType()));
     moduleTranslation.mapValue(args[i], var);
-    privateReductionVariables.push_back(var);
+    privateReductionVariables[i] = var;
     reductionVariableMap.try_emplace(loop.getReductionVars()[i], var);
   }
 }
@@ -911,7 +911,8 @@ convertOmpWsloop(Operation &opInst, llvm::IRBuilderBase &builder,
   llvm::OpenMPIRBuilder::InsertPointTy allocaIP =
       findAllocaInsertPoint(builder, moduleTranslation);
 
-  SmallVector<llvm::Value *> privateReductionVariables;
+  SmallVector<llvm::Value *> privateReductionVariables(
+      wsloopOp.getNumReductionVars());
   DenseMap<Value, llvm::Value *> reductionVariableMap;
   allocByValReductionVars(wsloopOp, builder, moduleTranslation, allocaIP,
                           reductionDecls, privateReductionVariables,
@@ -942,7 +943,7 @@ convertOmpWsloop(Operation &opInst, llvm::IRBuilderBase &builder,
       // ptr
       builder.CreateStore(phis[0], var);
 
-      privateReductionVariables.push_back(var);
+      privateReductionVariables[i] = var;
       moduleTranslation.mapValue(reductionArgs[i], phis[0]);
       reductionVariableMap.try_emplace(wsloopOp.getReductionVars()[i], phis[0]);
     } else {
@@ -1140,7 +1141,8 @@ convertOmpParallel(omp::ParallelOp opInst, llvm::IRBuilderBase &builder,
   // Collect reduction declarations
   SmallVector<omp::DeclareReductionOp> reductionDecls;
   collectReductionDecls(opInst, reductionDecls);
-  SmallVector<llvm::Value *> privateReductionVariables;
+  SmallVector<llvm::Value *> privateReductionVariables(
+      opInst.getNumReductionVars());
 
   auto bodyGenCB = [&](InsertPointTy allocaIP, InsertPointTy codeGenIP) {
     // Allocate reduction vars
@@ -1154,6 +1156,21 @@ convertOmpParallel(omp::ParallelOp opInst, llvm::IRBuilderBase &builder,
     MutableArrayRef<BlockArgument> reductionArgs =
         opInst.getRegion().getArguments().take_back(
             opInst.getNumReductionVars());
+
+    llvm::BasicBlock *initBlock = splitBB(builder, true, "omp.reduction.init");
+    allocaIP =
+        InsertPointTy(allocaIP.getBlock(),
+                      allocaIP.getBlock()->getTerminator()->getIterator());
+    SmallVector<llvm::Value *> byRefVars(opInst.getNumReductionVars());
+    for (unsigned i = 0; i < opInst.getNumReductionVars(); ++i) {
+      if (isByRef[i]) {
+        // Allocate reduction variable (which is a pointer to the real reduciton
+        // variable allocated in the inlined region)
+        byRefVars[i] = builder.CreateAlloca(
+            moduleTranslation.convertType(reductionDecls[i].getType()));
+      }
+    }
+
     for (unsigned i = 0; i < opInst.getNumReductionVars(); ++i) {
       SmallVector<llvm::Value *> phis;
 
@@ -1166,18 +1183,14 @@ convertOmpParallel(omp::ParallelOp opInst, llvm::IRBuilderBase &builder,
       assert(phis.size() == 1 &&
              "expected one value to be yielded from the "
              "reduction neutral element declaration region");
-      builder.restoreIP(allocaIP);
+      builder.SetInsertPoint(initBlock->getTerminator());
 
       if (isByRef[i]) {
-        // Allocate reduction variable (which is a pointer to the real reduciton
-        // variable allocated in the inlined region)
-        llvm::Value *var = builder.CreateAlloca(
-            moduleTranslation.convertType(reductionDecls[i].getType()));
         // Store the result of the inlined region to the allocated reduction var
         // ptr
-        builder.CreateStore(phis[0], var);
+        builder.CreateStore(phis[0], byRefVars[i]);
 
-        privateReductionVariables.push_back(var);
+        privateReductionVariables[i] = byRefVars[i];
         moduleTranslation.mapValue(reductionArgs[i], phis[0]);
         reductionVariableMap.try_emplace(opInst.getReductionVars()[i], phis[0]);
       } else {
diff --git a/mlir/test/Target/LLVMIR/openmp-parallel-reduction-cleanup.mlir b/mlir/test/Target/LLVMIR/openmp-parallel-reduction-cleanup.mlir
index 84a487c..8afa89f 100644
--- a/mlir/test/Target/LLVMIR/openmp-parallel-reduction-cleanup.mlir
+++ b/mlir/test/Target/LLVMIR/openmp-parallel-reduction-cleanup.mlir
@@ -55,11 +55,11 @@
 
 // Private reduction variable and its initialization.
 // CHECK: %tid.addr.local = alloca i32
-// CHECK: %[[MALLOC_I:.+]] = call ptr @malloc(i64 4)
 // CHECK: %[[PRIV_PTR_I:.+]] = alloca ptr
+// CHECK: %[[PRIV_PTR_J:.+]] = alloca ptr
+// CHECK: %[[MALLOC_I:.+]] = call ptr @malloc(i64 4)
 // CHECK: store ptr %[[MALLOC_I]], ptr %[[PRIV_PTR_I]]
 // CHECK: %[[MALLOC_J:.+]] = call ptr @malloc(i64 4)
-// CHECK: %[[PRIV_PTR_J:.+]] = alloca ptr
 // CHECK: store ptr %[[MALLOC_J]], ptr %[[PRIV_PTR_J]]
 
 // Call to the reduction function.
diff --git a/mlir/test/Target/LLVMIR/openmp-reduction-init-arg.mlir b/mlir/test/Target/LLVMIR/openmp-reduction-init-arg.mlir
index f4b77cb..361905f 100644
--- a/mlir/test/Target/LLVMIR/openmp-reduction-init-arg.mlir
+++ b/mlir/test/Target/LLVMIR/openmp-reduction-init-arg.mlir
@@ -59,13 +59,15 @@ module {
 // CHECK:         %[[VAL_17:.*]] = load i32, ptr %[[VAL_18:.*]], align 4
 // CHECK:         store i32 %[[VAL_17]], ptr %[[VAL_16]], align 4
 // CHECK:         %[[VAL_19:.*]] = load i32, ptr %[[VAL_16]], align 4
-// CHECK:         %[[VAL_20:.*]] = load { ptr, i64, i32, i8, i8, i8, i8, [1 x [3 x i64]] }, ptr %[[VAL_13]], align 8
 // CHECK:         %[[VAL_21:.*]] = alloca ptr, align 8
+// CHECK:         %[[VAL_23:.*]] = alloca ptr, align 8
+// CHECK:         %[[VAL_20:.*]] = load { ptr, i64, i32, i8, i8, i8, i8, [1 x [3 x i64]] }, ptr %[[VAL_13]], align 8
+// CHECK:         %[[VAL_24:.*]] = alloca [2 x ptr], align 8
+// CHECK:         br label %[[INIT_LABEL:.*]]
+// CHECK: [[INIT_LABEL]]:
 // CHECK:         store ptr %[[VAL_13]], ptr %[[VAL_21]], align 8
 // CHECK:         %[[VAL_22:.*]] = load { ptr, i64, i32, i8, i8, i8, i8, [1 x [3 x i64]] }, ptr %[[VAL_15]], align 8
-// CHECK:         %[[VAL_23:.*]] = alloca ptr, align 8
 // CHECK:         store ptr %[[VAL_15]], ptr %[[VAL_23]], align 8
-// CHECK:         %[[VAL_24:.*]] = alloca [2 x ptr], align 8
 // CHECK:         br label %[[VAL_25:.*]]
 // CHECK:       omp.par.region:                                   ; preds = %[[VAL_26:.*]]
 // CHECK:         br label %[[VAL_27:.*]]