[flang-commits] [flang] de3ff7e - [flang][FIR][Mem2Reg] Do not emit potentially wrong debug info (#194837)

[via flang-commits]

Author: Ivan R. Ivanov
Date: 2026-04-29T17:47:24Z
New Revision: de3ff7e2ac27c579844e912854bc5679e5d1f99b

URL: https://github.com/llvm/llvm-project/commit/de3ff7e2ac27c579844e912854bc5679e5d1f99b
DIFF: https://github.com/llvm/llvm-project/commit/de3ff7e2ac27c579844e912854bc5679e5d1f99b.diff

LOG: [flang][FIR][Mem2Reg] Do not emit potentially wrong debug info (#194837)

When mem2reg replaces values, it can potentially replace a value that is
stored before a fir.declare comes in scope, when the fir.declare was
inlined from another routine. When we emit a declare_value op for such a
variable, it can potentially break dominance with regards to the
fir.dummy_scope op.

Do not emit fir.declare_value op in such cases to prevent compiler
crashes.

Added: 
    

Modified: 
    flang/lib/Optimizer/Dialect/FIROps.cpp
    flang/test/Fir/mem2reg.mlir

Removed: 
    


################################################################################
diff  --git a/flang/lib/Optimizer/Dialect/FIROps.cpp b/flang/lib/Optimizer/Dialect/FIROps.cpp
index b412bc66718ac..8b730aba92d2b 100644
--- a/flang/lib/Optimizer/Dialect/FIROps.cpp
+++ b/flang/lib/Optimizer/Dialect/FIROps.cpp
@@ -5646,8 +5646,13 @@ void fir::DeclareOp::visitReplacedValues(
     llvm::ArrayRef<std::pair<mlir::Operation *, mlir::Value>> definitions,
     mlir::OpBuilder &builder) {
   for (auto [op, value] : definitions) {
+    // Do not emit DeclareValue when we have a dummy scope as this can
+    // potentially result in us generating it where the DummyScope does not
+    // dominate it. This can happen after inlining.
+    if (getDummyScope())
+      continue;
     builder.setInsertionPointAfter(op);
-    fir::DeclareValueOp::create(builder, getLoc(), value, getDummyScope(),
+    fir::DeclareValueOp::create(builder, getLoc(), value, nullptr,
                                 getUniqNameAttr(), getFortranAttrsAttr(),
                                 getDataAttrAttr(), getDummyArgNoAttr());
   }

diff  --git a/flang/test/Fir/mem2reg.mlir b/flang/test/Fir/mem2reg.mlir
index 5109c2ac3001b..41f894a2f9473 100644
--- a/flang/test/Fir/mem2reg.mlir
+++ b/flang/test/Fir/mem2reg.mlir
@@ -215,3 +215,21 @@ func.func @loop_conditional_update(%arg0: i32, %cdt: i1) -> i32 {
   %result = fir.load %declare : !fir.ref<i32>
   return %result : i32
 }
+
+// -----
+
+// Make sure we do not generate fir.declare_value for a replaced value
+// fir.declare with dummy_scope. This can result in the declare_value being
+// inserted before the dummy_scope it uses as would be the case here.
+
+// CHECK-LABEL: func.func @dummy_scope(
+// CHECK-NOT: fir.declare_value
+func.func @dummy_scope(%arg : i32) {
+  %alloca = fir.alloca i32 {adapt.valuebyref}
+  fir.store %arg to %alloca : !fir.ref<i32>
+  %scope = fir.dummy_scope : !fir.dscope
+  %declare = fir.declare %alloca dummy_scope %scope arg 1 {fortran_attrs = #fir.var_attrs<intent_in>, uniq_name = "foo"} : (!fir.ref<i32>, !fir.dscope) -> !fir.ref<i32>
+  %result = fir.load %declare : !fir.ref<i32>
+  fir.call @use(%result) : (i32) -> ()
+  return
+}