[llvm] [flang] Blank-fill internal list-directed record when no output is emitted (PR #213205)

[via llvm-commits]

https://github.com/ejose02 updated https://github.com/llvm/llvm-project/pull/213205

>From 5436767daf1e5e7b722045adfe4a278378b1347e Mon Sep 17 00:00:00 2001
From: ejose <ejose at amd.com>
Date: Fri, 31 Jul 2026 05:15:53 +0000
Subject: [PATCH] [flang] Blank-fill internal list-directed record when no
 output is emitted

Fixes #205989

Root cause: CompleteOperation() only called AdvanceRecord() when furthestPositionInRecord > 0, so zero-byte writes skipped blank-fill.

Fix: always call AdvanceRecord() for internal list-directed output. Added test for validation.
---
 flang-rt/lib/runtime/io-stmt.cpp                   |  4 +---
 flang-rt/unittests/Runtime/NumericalFormatTest.cpp | 14 ++++++++++++++
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/flang-rt/lib/runtime/io-stmt.cpp b/flang-rt/lib/runtime/io-stmt.cpp
index 08931fc781428..56996380ffa66 100644
--- a/flang-rt/lib/runtime/io-stmt.cpp
+++ b/flang-rt/lib/runtime/io-stmt.cpp
@@ -219,9 +219,7 @@ template <Direction DIR>
 void InternalListIoStatementState<DIR>::CompleteOperation() {
   if (!this->completedOperation()) {
     if constexpr (DIR == Direction::Output) {
-      if (unit_.furthestPositionInRecord > 0) {
-        unit_.AdvanceRecord(*this);
-      }
+      unit_.AdvanceRecord(*this);
     }
     IoStatementBase::CompleteOperation();
   }
diff --git a/flang-rt/unittests/Runtime/NumericalFormatTest.cpp b/flang-rt/unittests/Runtime/NumericalFormatTest.cpp
index 6af17e99418b4..f96e5cd294de8 100644
--- a/flang-rt/unittests/Runtime/NumericalFormatTest.cpp
+++ b/flang-rt/unittests/Runtime/NumericalFormatTest.cpp
@@ -244,6 +244,20 @@ TEST(IOApiTests, ListInputComplexRegressionTest) {
       << "', but got '" << output << "'";
 }
 
+TEST(IOApiTests, InternalListBlankFillNoOutputTest) {
+  static constexpr int bufferSize{10};
+  char buffer[bufferSize];
+  std::memcpy(buffer, "abcdefghij", bufferSize);
+  auto cookie{IONAME(BeginInternalListOutput)(buffer, bufferSize)};
+  auto status{IONAME(EndIoStatement)(cookie)};
+  ASSERT_EQ(status, 0) << "EndIoStatement failed, status "
+                       << static_cast<int>(status);
+  EXPECT_TRUE(
+      CompareFormattedStrings("          ", std::string{buffer, bufferSize}))
+      << "Expected all blanks but got '" << std::string{buffer, bufferSize}
+      << "'";
+}
+
 TEST(IOApiTests, DescriptorOutputTest) {
   static constexpr int bufferSize{10};
   char buffer[bufferSize];