Index: clang/lib/Basic/Targets/AVR.cpp
===================================================================
--- clang/lib/Basic/Targets/AVR.cpp
+++ clang/lib/Basic/Targets/AVR.cpp
@@ -377,7 +377,9 @@
                                      MacroBuilder &Builder) const {
   Builder.defineMacro("AVR");
   Builder.defineMacro("__AVR");
+  Builder.defineMacro("__avr");
   Builder.defineMacro("__AVR__");
+  Builder.defineMacro("__avr__");
   Builder.defineMacro("__ELF__");
 
   if (!this->CPU.empty()) {
Index: compiler-rt/cmake/Modules/CompilerRTUtils.cmake
===================================================================
--- compiler-rt/cmake/Modules/CompilerRTUtils.cmake
+++ compiler-rt/cmake/Modules/CompilerRTUtils.cmake
@@ -168,6 +168,7 @@
   check_symbol_exists(__wasm32__ "" __WEBASSEMBLY32)
   check_symbol_exists(__wasm64__ "" __WEBASSEMBLY64)
   check_symbol_exists(__ve__ "" __VE)
+  check_symbol_exists(__avr__ "" __AVR)
   if(__ARM)
     add_default_target_arch(arm)
   elseif(__AARCH64)
@@ -212,6 +213,8 @@
     add_default_target_arch(wasm64)
   elseif(__VE)
     add_default_target_arch(ve)
+  elseif(__AVR)
+    add_default_target_arch(avr)
   endif()
 endmacro()
 
Index: compiler-rt/cmake/base-config-ix.cmake
===================================================================
--- compiler-rt/cmake/base-config-ix.cmake
+++ compiler-rt/cmake/base-config-ix.cmake
@@ -248,6 +248,8 @@
       test_target_arch(wasm64 "" "--target=wasm64-unknown-unknown")
     elseif("${COMPILER_RT_DEFAULT_TARGET_ARCH}" MATCHES "ve")
       test_target_arch(ve "__ve__" "--target=ve-unknown-none")
+    elseif("${COMPILER_RT_DEFAULT_TARGET_ARCH}" MATCHES "avr")
+      test_target_arch(avr "__avr__" "--target=avr")
     endif()
     set(COMPILER_RT_OS_SUFFIX "")
   endif()
Index: compiler-rt/cmake/builtin-config-ix.cmake
===================================================================
--- compiler-rt/cmake/builtin-config-ix.cmake
+++ compiler-rt/cmake/builtin-config-ix.cmake
@@ -52,6 +52,7 @@
 set(WASM32 wasm32)
 set(WASM64 wasm64)
 set(VE ve)
+set(AVR avr)
 
 if(APPLE)
   set(ARM64 arm64 arm64e)
@@ -63,7 +64,7 @@
   ${X86} ${X86_64} ${ARM32} ${ARM64}
   ${HEXAGON} ${MIPS32} ${MIPS64} ${PPC32} ${PPC64}
   ${RISCV32} ${RISCV64} ${SPARC} ${SPARCV9}
-  ${WASM32} ${WASM64} ${VE})
+  ${WASM32} ${WASM64} ${VE} ${AVR})
 
 include(CompilerRTUtils)
 include(CompilerRTDarwinUtils)
Index: compiler-rt/cmake/config-ix.cmake
===================================================================
--- compiler-rt/cmake/config-ix.cmake
+++ compiler-rt/cmake/config-ix.cmake
@@ -203,8 +203,10 @@
 
 # Detect whether the current target platform is 32-bit or 64-bit, and setup
 # the correct commandline flags needed to attempt to target 32-bit and 64-bit.
+# AVR and MSP430 are omitted since they have 16-bit pointers.
 if (NOT CMAKE_SIZEOF_VOID_P EQUAL 4 AND
-    NOT CMAKE_SIZEOF_VOID_P EQUAL 8)
+    NOT CMAKE_SIZEOF_VOID_P EQUAL 8 AND
+    NOT ${arch} MATCHES "avr|msp430")
   message(FATAL_ERROR "Please use architecture with 4 or 8 byte pointers.")
 endif()
 
Index: compiler-rt/lib/builtins/CMakeLists.txt
===================================================================
--- compiler-rt/lib/builtins/CMakeLists.txt
+++ compiler-rt/lib/builtins/CMakeLists.txt
@@ -668,6 +668,11 @@
   ${GENERIC_TF_SOURCES}
   ${GENERIC_SOURCES})
 
+set(avr_SOURCES
+  ${GENERIC_TF_SOURCES}
+  ${GENERIC_SOURCES}
+)
+
 add_custom_target(builtins)
 set_target_properties(builtins PROPERTIES FOLDER "Compiler-RT Misc")