diff --git a/INSTALL.md b/INSTALL.md
index bcc47e02b..4db678aab 100644
--- a/INSTALL.md
+++ b/INSTALL.md
@@ -15,8 +15,8 @@ NEW or CHANGED dependencies since the last major release are **bold**.
 * Build system: [CMake](https://cmake.org/) 3.12 or newer (tested through 3.21)
 
 * A suitable C++11 compiler to build OSL itself, which may be any of:
-   - GCC 4.8.5 or newer (tested through gcc 11)
-   - Clang 3.4 or newer (tested through clang 12)
+   - GCC 4.8.5 or newer (tested through gcc 11.2)
+   - Clang 3.4 or newer (tested through clang 13)
    - Microsoft Visual Studio 2015 or newer
    - Intel C++ compiler icc version 13 (?) or newer
 
@@ -43,8 +43,8 @@ NEW or CHANGED dependencies since the last major release are **bold**.
     DYLD_LIBRARY_PATH on OS X) and then OSL's build scripts will be able
     to find it.
 
-* **[LLVM](http://www.llvm.org) 7, 8, 9, 10, 11, or 12**, including
-  clang libraries.
+* **[LLVM](http://www.llvm.org) 7, 8, 9, 10, 11, 12, or 13**, including clang
+  libraries.
 
   Note that LLVM 10+ is not compatible with C++11, and requires C++14 or
   later. If you *must* build OSL with C++11, you need to use an LLVM that
@@ -52,8 +52,11 @@ NEW or CHANGED dependencies since the last major release are **bold**.
 
 * [Boost](https://www.boost.org) 1.55 or newer (tested through boost 1.76)
 * [Ilmbase or Imath](http://openexr.com/downloads.html) 2.0 or newer (tested through 3.1)
-* [Flex](https://github.com/westes/flex) and
-  [GNU Bison](https://www.gnu.org/software/bison/)
+* [Flex](https://github.com/westes/flex) 2.5.35 or newer and
+  [GNU Bison](https://www.gnu.org/software/bison/) 2.7 or newer.
+  Note that on some MacOS/xcode releases, the system-installed Bison is too
+  old, and it's better to install a newer Bison (via Homebrew is one way to
+  do this easily).
 * [PugiXML](http://pugixml.org/)
 * (optional) [Partio](https://www.disneyanimation.com/technology/partio.html)
   If it is not found at build time, the OSL `pointcloud` functions will not
diff --git a/src/include/OSL/llvm_util.h b/src/include/OSL/llvm_util.h
index 20aa11a60..cb1e44e38 100644
--- a/src/include/OSL/llvm_util.h
+++ b/src/include/OSL/llvm_util.h
@@ -577,6 +577,9 @@ class OSLEXECPUBLIC LLVM_Util {
                     llvm::Value *src, int srcalign, int len);
 
     /// Dereference a pointer:  return *ptr
+    /// type is the type of the thing being pointed to.
+    llvm::Value *op_load (llvm::Type* type, llvm::Value *ptr);
+    // Blind pointer version that's deprecated as of LLVM13:
     llvm::Value *op_load (llvm::Value *ptr);
 
     /// Store to a dereferenced pointer:   *ptr = val
@@ -589,17 +592,25 @@ class OSLEXECPUBLIC LLVM_Util {
 
     /// Generate a GEP (get element pointer) where the element index is an
     /// llvm::Value, which can be generated from either a constant or a
-    /// runtime-computed integer element index.
+    /// runtime-computed integer element index. `type` is the type of the data
+    /// we're retrieving.
+    llvm::Value *GEP (llvm::Type* type, llvm::Value *ptr, llvm::Value *elem);
+    // Blind pointer version that's deprecated as of LLVM13:
     llvm::Value *GEP (llvm::Value *ptr, llvm::Value *elem);
 
     /// Generate a GEP (get element pointer) with an integer element
-    /// offset.
+    /// offset. `type` is the type of the data we're retrieving.
+    llvm::Value *GEP (llvm::Type* type, llvm::Value *ptr, int elem);
+    // Blind pointer version that's deprecated as of LLVM13:
     llvm::Value *GEP (llvm::Value *ptr, int elem);
 
     /// Generate a GEP (get element pointer) with two integer element
     /// offsets.  This is just a special (and common) case of GEP where
     /// we have a 2-level hierarchy and we have fixed element indices
-    /// that are known at compile time.
+    /// that are known at compile time.  `type` is the type of the data we're
+    /// retrieving.
+    llvm::Value *GEP (llvm::Type* type, llvm::Value *ptr, int elem1, int elem2);
+    // Blind pointer version that's deprecated as of LLVM13:
     llvm::Value *GEP (llvm::Value *ptr, int elem1, int elem2);
 
     // Arithmetic ops.  It auto-detects the type (int vs float).
diff --git a/src/liboslexec/llvm_util.cpp b/src/liboslexec/llvm_util.cpp
index f06c53de3..45e0b3e46 100644
--- a/src/liboslexec/llvm_util.cpp
+++ b/src/liboslexec/llvm_util.cpp
@@ -2591,10 +2591,18 @@ LLVM_Util::op_memcpy (llvm::Value *dst, int dstalign,
 
 
 
+llvm::Value *
+LLVM_Util::op_load (llvm::Type* type, llvm::Value* ptr)
+{
+    return builder().CreateLoad (type, ptr);
+}
+
+
+
 llvm::Value *
 LLVM_Util::op_load (llvm::Value *ptr)
 {
-    return builder().CreateLoad (ptr);
+    return op_load(ptr->getType()->getPointerElementType(), ptr);
 }
 
 
@@ -2607,10 +2615,27 @@ LLVM_Util::op_store (llvm::Value *val, llvm::Value *ptr)
 
 
 
+llvm::Value *
+LLVM_Util::GEP (llvm::Type* type, llvm::Value* ptr, llvm::Value* elem)
+{
+    return builder().CreateGEP(type, ptr, elem);
+}
+
+
+
 llvm::Value *
 LLVM_Util::GEP (llvm::Value *ptr, llvm::Value *elem)
 {
-    return builder().CreateGEP (ptr, elem);
+    return GEP(ptr->getType()->getScalarType()->getPointerElementType(), ptr,
+               elem);
+}
+
+
+
+llvm::Value *
+LLVM_Util::GEP (llvm::Type* type, llvm::Value* ptr, int elem)
+{
+    return builder().CreateConstGEP1_32(type, ptr, elem);
 }
 
 
@@ -2618,7 +2643,16 @@ LLVM_Util::GEP (llvm::Value *ptr, llvm::Value *elem)
 llvm::Value *
 LLVM_Util::GEP (llvm::Value *ptr, int elem)
 {
-    return builder().CreateConstGEP1_32 (ptr, elem);
+    return GEP(ptr->getType()->getScalarType()->getPointerElementType(), ptr,
+               elem);
+}
+
+
+
+llvm::Value *
+LLVM_Util::GEP(llvm::Type* type, llvm::Value* ptr, int elem1, int elem2)
+{
+    return builder().CreateConstGEP2_32 (type, ptr, elem1, elem2);
 }
 
 
@@ -2626,7 +2660,8 @@ LLVM_Util::GEP (llvm::Value *ptr, int elem)
 llvm::Value *
 LLVM_Util::GEP (llvm::Value *ptr, int elem1, int elem2)
 {
-    return builder().CreateConstGEP2_32 (nullptr, ptr, elem1, elem2);
+    return GEP(ptr->getType()->getScalarType()->getPointerElementType(), ptr,
+               elem1, elem2);
 }
 
 
diff --git a/src/liboslexec/runtimeoptimize.cpp b/src/liboslexec/runtimeoptimize.cpp
index 3aafb0896..76edfae6b 100644
--- a/src/liboslexec/runtimeoptimize.cpp
+++ b/src/liboslexec/runtimeoptimize.cpp
@@ -2301,7 +2301,6 @@ RuntimeOptimizer::optimize_instance ()
     // passes, but we have a hard cutoff just to be sure we don't
     // ever get into an infinite loop from an unforseen cycle where we
     // end up inadvertently transforming A => B => A => etc.
-    int totalchanged = 0;
     int reallydone = 0;   // Force a few passes after we think we're done
     int npasses = shadingsys().opt_passes();
     for (m_pass = 0;  m_pass < npasses;  ++m_pass) {
@@ -2362,7 +2361,6 @@ RuntimeOptimizer::optimize_instance ()
         // If nothing changed, we're done optimizing.  But wait, it may be
         // that after re-tracking variable lifetimes, we can notice new
         // optimizations!  So force another pass, then we're really done.
-        totalchanged += changed;
         if (changed < 1) {
             if (++reallydone > 3)
                 break;