[flang][Alias Analysis] not all block arguments are dummy arguments (#92156)

Arguments to openmp regions should not be tagged as dummy arguments.
This is particularly unsafe because these openmp blocks will eventually
be inlined into the calling function, where they will trivially alias
with other values inside of the calling function.

This is probably a theoretical issue because the calls to openmp runtime
function calls would act as barriers, preventing optimizations that are
too aggressive. But a lot more thought would need to go into a bet like
that.

This came out of discussion on
#92036

Author: tblah

flang/lib/Optimizer/Analysis/AliasAnalysis.cpp

@@ -33,7 +33,11 @@ static bool isDummyArgument(mlir::Value v) {
   if (!blockArg)
     return false;
 
-  return blockArg.getOwner()->isEntryBlock();
+  mlir::Block *owner = blockArg.getOwner();
+  if (!owner->isEntryBlock() ||
+      !mlir::isa<mlir::FunctionOpInterface>(owner->getParentOp()))
+    return false;
+  return true;
 }
 
 /// Temporary function to skip through all the no op operations

flang/lib/Optimizer/Transforms/AddAliasTags.cpp

@@ -105,6 +105,7 @@ static std::string getFuncArgName(mlir::Value arg) {
          "arg is a function argument");
   mlir::FunctionOpInterface func = mlir::dyn_cast<mlir::FunctionOpInterface>(
       blockArg.getOwner()->getParentOp());
+  assert(func && "This is not a function argument");
   mlir::StringAttr attr = func.getArgAttrOfType<mlir::StringAttr>(
       blockArg.getArgNumber(), "fir.bindc_name");
   if (!attr)

flang/test/Transforms/tbaa.fir

@@ -173,3 +173,40 @@
 // CHECK:           fir.store %[[VAL_8]] to %[[VAL_12]] : !fir.ref<i32>
 // CHECK:           return
 // CHECK:         }
+
+// -----
+
+// Make sure we don't mistake other block arguments as dummy arguments:
+
+omp.declare_reduction @add_reduction_i32 : i32 init {
+^bb0(%arg0: i32):
+  %c0_i32 = arith.constant 0 : i32
+  omp.yield(%c0_i32 : i32)
+} combiner {
+^bb0(%arg0: i32, %arg1: i32):
+  %0 = arith.addi %arg0, %arg1 : i32
+  omp.yield(%0 : i32)
+}
+
+func.func @_QQmain() attributes {fir.bindc_name = "reduce"} {
+  %c10_i32 = arith.constant 10 : i32
+  %c6_i32 = arith.constant 6 : i32
+  %c-1_i32 = arith.constant -1 : i32
+  %0 = fir.address_of(@_QFEi) : !fir.ref<i32>
+  %1 = fir.declare %0 {uniq_name = "_QFEi"} : (!fir.ref<i32>) -> !fir.ref<i32>
+  omp.parallel reduction(@add_reduction_i32 %1 -> %arg0 : !fir.ref<i32>) {
+// CHECK: omp.parallel reduction({{.*}}) {
+    %8 = fir.declare %arg0 {uniq_name = "_QFEi"} : (!fir.ref<i32>) -> !fir.ref<i32>
+// CHECK-NEXT: %[[DECL:.*]] = fir.declare
+    fir.store %c-1_i32 to %8 : !fir.ref<i32>
+// CHECK-NOT: fir.store %{{.*}} to %[[DECL]] {tbaa = %{{.*}}} : !fir.ref<i32>
+// CHECK:     fir.store %{{.*}} to %[[DECL]] : !fir.ref<i32>
+    omp.terminator
+  }
+  return
+}
+
+fir.global internal @_QFEi : i32 {
+  %c0_i32 = arith.constant 0 : i32
+  fir.has_value %c0_i32 : i32
+}