[flang] [llvm] [llvm][flang] Silence warning, resume -Werror builds of flang (PR #175053)

[Peter Klausler via llvm-commits]

https://github.com/klausler updated https://github.com/llvm/llvm-project/pull/175053

>From f28e541d8648979fa0598417c0e7e2f5ebd85946 Mon Sep 17 00:00:00 2001
From: Peter Klausler <pklausler at nvidia.com>
Date: Thu, 8 Jan 2026 11:20:31 -0800
Subject: [PATCH] [llvm][flang] Silence warning, resume -Werror builds of flang

Add (void) uses of two parameters to dodge a C++ compiler warning
that has broken -Werror builds of flang since 9-28-25, and restore
that option as the default for flang builds.

Also tweak the source to remove a work-around for an MSVC bug
(presumed to have been fixed) that now produces a warning in CI.
---
 flang/CMakeLists.txt                | 2 +-
 flang/lib/Evaluate/fold-real.cpp    | 8 +-------
 llvm/include/llvm/ADT/SmallVector.h | 2 ++
 3 files changed, 4 insertions(+), 8 deletions(-)

diff --git a/flang/CMakeLists.txt b/flang/CMakeLists.txt
index c01eb56d5e496..390cfe749f962 100644
--- a/flang/CMakeLists.txt
+++ b/flang/CMakeLists.txt
@@ -37,7 +37,7 @@ if (CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR AND NOT MSVC_IDE)
           `CMakeFiles'. Please delete them.")
 endif()
 
-option(FLANG_ENABLE_WERROR "Fail and stop building flang if a warning is triggered." OFF)
+option(FLANG_ENABLE_WERROR "Fail and stop building flang if a warning is triggered." ON)
 
 # Check for a standalone build and configure as appropriate from
 # there.
diff --git a/flang/lib/Evaluate/fold-real.cpp b/flang/lib/Evaluate/fold-real.cpp
index 1ff941053a82e..907d01b005a04 100644
--- a/flang/lib/Evaluate/fold-real.cpp
+++ b/flang/lib/Evaluate/fold-real.cpp
@@ -387,13 +387,7 @@ Expr<Type<TypeCategory::Real, KIND>> FoldIntrinsicFunction(
                 ScalarFunc<T, T, TBY>(
                     [&](const Scalar<T> &x, const Scalar<TBY> &y) -> Scalar<T> {
                       ValueWithRealFlags<Scalar<T>> result{
-                          x.
-// MSVC chokes on the keyword "template" here in a call to a
-// member function template.
-#ifndef _MSC_VER
-                          template
-#endif
-                          SCALE<Scalar<TBY>>(y)};
+                          x.template SCALE<Scalar<TBY>>(y)};
                       if (result.flags.test(RealFlag::Overflow)) {
                         context.Warn(common::UsageWarning::FoldingException,
                             "SCALE/IEEE_SCALB intrinsic folding overflow"_warn_en_US);
diff --git a/llvm/include/llvm/ADT/SmallVector.h b/llvm/include/llvm/ADT/SmallVector.h
index 51109d1f416f2..23d40c3e07675 100644
--- a/llvm/include/llvm/ADT/SmallVector.h
+++ b/llvm/include/llvm/ADT/SmallVector.h
@@ -211,6 +211,8 @@ class SmallVectorTemplateCommon
       this->assertSafeToReferenceAfterResize(From, 0);
       this->assertSafeToReferenceAfterResize(To - 1, 0);
     }
+    (void)From;
+    (void)To;
   }
 
   /// Check whether any part of the range will be invalidated by growing.