[flang] support fir.alloca operations inside of omp reduction ops

flang/lib/Optimizer/Builder/FIRBuilder.cpp

@@ -208,6 +208,8 @@ mlir::Block *fir::FirOpBuilder::getAllocaBlock() {
               .getParentOfType<mlir::omp::OutlineableOpenMPOpInterface>()) {
     return ompOutlineableIface.getAllocaBlock();
   }
+  if (mlir::isa<mlir::omp::ReductionDeclareOp>(getRegion().getParentOp()))
+    return &getRegion().front();
   if (auto accRecipeIface =
           getRegion().getParentOfType<mlir::acc::RecipeInterface>()) {
     return accRecipeIface.getAllocaBlock(getRegion());

flang/lib/Optimizer/CodeGen/CodeGen.cpp

@@ -410,8 +410,15 @@ class FIROpConversion : public mlir::ConvertOpToLLVMPattern<FromOp> {
       mlir::ConversionPatternRewriter &rewriter) const {
     auto thisPt = rewriter.saveInsertionPoint();
     mlir::Operation *parentOp = rewriter.getInsertionBlock()->getParentOp();
-    mlir::Block *insertBlock = getBlockForAllocaInsert(parentOp);
-    rewriter.setInsertionPointToStart(insertBlock);
+    if (mlir::isa<mlir::omp::ReductionDeclareOp>(parentOp)) {
+      // ReductionDeclareOp has multiple child regions. We want to get the first
+      // block of whichever of those regions we are currently in
+      mlir::Region *parentRegion = rewriter.getInsertionBlock()->getParent();
+      rewriter.setInsertionPointToStart(&parentRegion->front());
+    } else {
+      mlir::Block *insertBlock = getBlockForAllocaInsert(parentOp);
+      rewriter.setInsertionPointToStart(insertBlock);
+    }
     auto size = genI32Constant(loc, rewriter, 1);
     unsigned allocaAs = getAllocaAddressSpace(rewriter);
     unsigned programAs = getProgramAddressSpace(rewriter);

flang/test/Fir/omp-reduction-embox-codegen.fir

@@ -0,0 +1,36 @@
+// RUN: tco %s | FileCheck %s
+
+// the fir.embox in the init region is turned into an alloca for the box. Test
+// that CodeGen.cpp knows where to place an alloca when it is inside of an
+// omp.reduction.declare
+
+// regretably this has to be nonsense IR because we need the subsequent patches
+// to process anything useful
+
+omp.reduction.declare @test_reduction : !fir.ref<!fir.box<i32>> init {
+^bb0(%arg0: !fir.ref<!fir.box<i32>>):
+  %0 = fir.alloca !fir.box<i32>
+  %1 = fir.alloca i32
+  %2 = fir.embox %1 : (!fir.ref<i32>) -> !fir.box<i32>
+
+  // use the embox for something so it isn't removed
+  fir.store %2 to %0 : !fir.ref<!fir.box<i32>>
+
+  omp.yield(%0 : !fir.ref<!fir.box<i32>>)
+} combiner {
+^bb0(%arg0: !fir.ref<!fir.box<i32>>, %arg1: !fir.ref<!fir.box<i32>>):
+  %0 = fir.undefined !fir.ref<!fir.box<i32>>
+  omp.yield(%0 : !fir.ref<!fir.box<i32>>)
+}
+
+func.func @_QQmain() attributes {fir.bindc_name = "reduce"} {
+  %4 = fir.alloca !fir.box<i32>
+  omp.parallel byref reduction(@test_reduction %4 -> %arg0 : !fir.ref<!fir.box<i32>>) {
+    omp.terminator
+  }
+  return
+}
+
+// basically we are testing that there isn't a crash
+// CHECK-LABEL: define void @_QQmain
+// CHECK-NEXT:    alloca { ptr, i64, i32, i8, i8, i8, i8 }, i64 1, align 8