-*- Mode: diff -*-
diff --git a/core/fpdfdoc/cpdf_metadata.cpp b/core/fpdfdoc/cpdf_metadata.cpp
index 323de4ffc..f11a0b0ad 100644
--- a/core/fpdfdoc/cpdf_metadata.cpp
+++ b/core/fpdfdoc/cpdf_metadata.cpp
@@ -74,7 +74,7 @@ std::vector<UnsupportedFeature> CPDF_Metadata::CheckForSharedForm() const {
   CFX_XMLParser parser(stream);
   std::unique_ptr<CFX_XMLDocument> doc = parser.Parse();
   if (!doc)
-    return {};
+    return std::vector<UnsupportedFeature>();
 
   std::vector<UnsupportedFeature> unsupported;
   CheckForSharedFormInternal(doc->GetRoot(), &unsupported);
diff --git a/third_party/base/span.h b/third_party/base/span.h
index ec9f9903f..1c17ad091 100644
--- a/third_party/base/span.h
+++ b/third_party/base/span.h
@@ -208,7 +208,7 @@ class span {
   // Conversions from spans of compatible types: this allows a span<T> to be
   // seamlessly used as a span<const T>, but not the other way around.
   template <typename U, typename = internal::EnableIfLegalSpanConversion<U, T>>
-  constexpr span(const span<U>& other) : span(other.data(), other.size()) {}
+  span(const span<U>& other) : span(other.data(), other.size()) {}
   span& operator=(const span& other) noexcept {
     if (this != &other) {
       ReleaseEmptySpan();
diff --git a/third_party/base/span.h b/third_party/base/span.h
index 0fb627ba8..dda1fc8bc 100644
--- a/third_party/base/span.h
+++ b/third_party/base/span.h
@@ -204,7 +204,7 @@ class span {
   // size()|.
   template <typename Container,
             typename = internal::EnableIfSpanCompatibleContainer<Container, T>>
-  constexpr span(Container& container)
+  span(Container& container)
       : span(container.data(), container.size()) {}
   template <
       typename Container,
diff --git a/core/fxcodec/jpx/cjpx_decoder.cpp b/core/fxcodec/jpx/cjpx_decoder.cpp
index d8875786c..bc019ebe1 100644
--- a/core/fxcodec/jpx/cjpx_decoder.cpp
+++ b/core/fxcodec/jpx/cjpx_decoder.cpp
@@ -73,7 +73,7 @@ absl::optional<OpjImageRgbData> alloc_rgb(size_t size) {
   if (!data.b)
     return absl::nullopt;
 
-  return data;
+  return std::move(data);
 }
 
 void sycc_to_rgb(int offset,
diff --git a/core/fxge/cfx_font.cpp b/core/fxge/cfx_font.cpp
index 8b3a72700..ea1db23f4 100644
--- a/core/fxge/cfx_font.cpp
+++ b/core/fxge/cfx_font.cpp
@@ -47,25 +47,9 @@ struct OUTLINE_PARAMS {
 // TODO(crbug.com/pdfium/1400): When FT_Done_MM_Var() is more likely to be
 // available to all users in the future, remove FreeMMVar() and use
 // FT_Done_MM_Var() directly.
-//
-// Use weak symbols to check if FT_Done_MM_Var() is available at runtime.
-#if !BUILDFLAG(IS_WIN)
-extern "C" __attribute__((weak)) decltype(FT_Done_MM_Var) FT_Done_MM_Var;
-#endif
 
 void FreeMMVar(FXFT_FaceRec* rec, FXFT_MM_VarPtr variation_desc) {
-#if BUILDFLAG(IS_WIN)
-  // Assume `use_system_freetype` GN var is never set on Windows.
-  constexpr bool has_ft_done_mm_var_func = true;
-#else
-  static const bool has_ft_done_mm_var_func = !!FT_Done_MM_Var;
-#endif
-  if (has_ft_done_mm_var_func) {
-    FT_Done_MM_Var(CFX_GEModule::Get()->GetFontMgr()->GetFTLibrary(),
-                   variation_desc);
-  } else {
     FXFT_Free(rec, variation_desc);
-  }
 }
 
 FX_RECT FXRectFromFTPos(FT_Pos left, FT_Pos top, FT_Pos right, FT_Pos bottom) {
diff --git a/third_party/base/numerics/safe_conversions_impl.h b/third_party/base/numerics/safe_conversions_impl.h
index 4d8a7b7d9..d14c6dc06 100644
--- a/third_party/base/numerics/safe_conversions_impl.h
+++ b/third_party/base/numerics/safe_conversions_impl.h
@@ -88,7 +88,7 @@ constexpr typename std::make_unsigned<T>::type SafeUnsignedAbs(T value) {
 
 // TODO(jschuh): Switch to std::is_constant_evaluated() once C++20 is supported.
 // Alternately, the usage could be restructured for "consteval if" in C++23.
-#define IsConstantEvaluated() (__builtin_is_constant_evaluated())
+#define IsConstantEvaluated() (false)
 
 // TODO(jschuh): Debug builds don't reliably propagate constants, so we restrict
 // some accelerated runtime paths to release builds until this can be forced
--- pdfium/core/fpdfapi/font/cpdf_cidfont.cpp.orig	2022-05-20 09:25:52.066728467 +0000
+++ pdfium/core/fpdfapi/font/cpdf_cidfont.cpp	2022-05-20 09:25:56.146736531 +0000
@@ -738,7 +738,7 @@
         uint32_t maccode = CharCodeFromUnicodeForFreetypeEncoding(
             FT_ENCODING_APPLE_ROMAN, name_unicode);
         index = maccode ? FT_Get_Char_Index(face, maccode)
-                        : FT_Get_Name_Index(face, name);
+                        : FT_Get_Name_Index(face, const_cast<char*>(name));
       }
       if (index == 0 || index == 0xffff)
         return charcode ? static_cast<int>(charcode) : -1;
--- pdfium/core/fpdfapi/font/cpdf_type1font.cpp.orig	2022-05-20 09:26:59.090862058 +0000
+++ pdfium/core/fpdfapi/font/cpdf_type1font.cpp	2022-05-20 09:27:33.810932435 +0000
@@ -260,7 +260,7 @@
                                           static_cast<uint32_t>(charcode));
       if (name) {
         m_Encoding.SetUnicode(charcode, UnicodeFromAdobeName(name));
-        m_GlyphIndex[charcode] = FT_Get_Name_Index(m_Font.GetFaceRec(), name);
+        m_GlyphIndex[charcode] = FT_Get_Name_Index(m_Font.GetFaceRec(), const_cast<char*>(name));
       } else {
         m_GlyphIndex[charcode] = FT_Get_Char_Index(
             m_Font.GetFaceRec(), static_cast<uint32_t>(charcode));
@@ -291,7 +291,7 @@
       continue;
 
     m_Encoding.SetUnicode(charcode, UnicodeFromAdobeName(name));
-    m_GlyphIndex[charcode] = FT_Get_Name_Index(m_Font.GetFaceRec(), name);
+    m_GlyphIndex[charcode] = FT_Get_Name_Index(m_Font.GetFaceRec(), const_cast<char*>(name));
     if (m_GlyphIndex[charcode] != 0)
       continue;
 
--- pdfium/core/fpdfapi/font/cpdf_truetypefont.cpp.orig	2022-05-20 09:26:12.066767996 +0000
+++ pdfium/core/fpdfapi/font/cpdf_truetypefont.cpp	2022-05-20 09:26:46.690836923 +0000
@@ -90,7 +90,7 @@
               FT_ENCODING_APPLE_ROMAN,
               m_Encoding.UnicodeFromCharCode(charcode));
           if (!maccode) {
-            m_GlyphIndex[charcode] = FT_Get_Name_Index(face, name);
+            m_GlyphIndex[charcode] = FT_Get_Name_Index(face, const_cast<char*>(name));
           } else {
             m_GlyphIndex[charcode] = FT_Get_Char_Index(face, maccode);
           }
@@ -104,7 +104,7 @@
         m_GlyphIndex[charcode] = FT_Get_Char_Index(face, 32);
         continue;
       }
-      m_GlyphIndex[charcode] = FT_Get_Name_Index(face, name);
+      m_GlyphIndex[charcode] = FT_Get_Name_Index(face, const_cast<char*>(name));
       if (m_GlyphIndex[charcode] != 0 || !bToUnicode)
         continue;
 
diff --git a/third_party/libopenjpeg/openjpeg.c b/third_party/libopenjpeg/openjpeg.c
index 29d3ee528..d5c7a1bc9 100644
--- a/third_party/libopenjpeg/openjpeg.c
+++ b/third_party/libopenjpeg/openjpeg.c
@@ -433,7 +433,7 @@ OPJ_BOOL OPJ_CALLCONV opj_setup_decoder(opj_codec_t *p_codec,
     return OPJ_FALSE;
 }
 
-OPJ_API OPJ_BOOL OPJ_CALLCONV opj_decoder_set_strict_mode(opj_codec_t *p_codec,
+OPJ_BOOL OPJ_CALLCONV opj_decoder_set_strict_mode(opj_codec_t *p_codec,
         OPJ_BOOL strict)
 {
     if (p_codec) {