diff --git a/Makefile b/Makefile
index 097da238..10d51bd5 100644
--- a/Makefile
+++ b/Makefile
@@ -109,14 +109,13 @@ else
     BUILD_VERSION:=$(GIT_REVISION)
 endif
 
-CXX=g++
-CPP=cpp
+CXX=clang++
 OPT=-O2
 CXXFLAGS=$(OPT) $(LLVM_CXXFLAGS) -I. -Iobjs/ -I$(CLANG_INCLUDE)  \
 	$(LLVM_VERSION_DEF) \
 	-Wall \
 	-DBUILD_DATE="\"$(BUILD_DATE)\"" -DBUILD_VERSION="\"$(BUILD_VERSION)\"" \
-	-Wno-sign-compare
+	-Wno-sign-compare -Wno-unused-function
 ifneq ($(LLVM_VERSION),LLVM_3_1)
 	CXXFLAGS+=-Werror
 endif
@@ -202,9 +201,14 @@ ispc: print_llvm_src dirs $(OBJS)
 	@$(CXX) $(OPT) $(LDFLAGS) -o $@ $(OBJS) $(ISPC_LIBS)
 
 # Use clang as a default compiler, instead of gcc
+# This is default now.
 clang: ispc
 clang: CXX=clang++
 
+# Use gcc as a default compiler, instead of gcc
+gcc: ispc
+gcc: CXX=clang++
+
 # Build ispc with address sanitizer instrumentation using clang compiler
 # Note that this is not portable build
 asan: clang
diff --git a/cbackend.cpp b/cbackend.cpp
index 7d4b4cfc..481ca3fd 100644
--- a/cbackend.cpp
+++ b/cbackend.cpp
@@ -3066,7 +3066,7 @@ void CWriter::visitReturnInst(llvm::ReturnInst &I) {
   // Don't output a void return if this is the last basic block in the function
   if (I.getNumOperands() == 0 &&
       &*--I.getParent()->getParent()->end() == I.getParent() &&
-      !I.getParent()->size() == 1) {
+      (!I.getParent()->size()) == 1) {
     return;
   }
 
diff --git a/examples/aobench_instrumented/Makefile b/examples/aobench_instrumented/Makefile
index 9921cf3e..d0b27cbf 100644
--- a/examples/aobench_instrumented/Makefile
+++ b/examples/aobench_instrumented/Makefile
@@ -1,5 +1,5 @@
 
-CXX=g++ -m64
+CXX=clang++ -m64
 CXXFLAGS=-Iobjs/ -g3 -Wall
 ISPC=ispc
 ISPCFLAGS=-O2 --instrument --arch=x86-64 --target=sse2
diff --git a/examples/common.mk b/examples/common.mk
index 367d3eb3..db7b8eee 100644
--- a/examples/common.mk
+++ b/examples/common.mk
@@ -3,14 +3,14 @@ TASK_CXX=../tasksys.cpp
 TASK_LIB=-lpthread
 TASK_OBJ=objs/tasksys.o
 
-CXX=g++
-CXXFLAGS=-Iobjs/ -O2
-CC=gcc
-CCFLAGS=-Iobjs/ -O2
+CXX=clang++
+CXXFLAGS+=-Iobjs/ -O2
+CC=clang
+CCFLAGS+=-Iobjs/ -O2
 
 LIBS=-lm $(TASK_LIB) -lstdc++
 ISPC=ispc
-ISPC_FLAGS=-O2
+ISPC_FLAGS+=-O2
 ISPC_HEADER=objs/$(ISPC_SRC:.ispc=_ispc.h)
 
 ARCH:=$(shell uname -m | sed -e s/x86_64/x86/ -e s/i686/x86/ -e s/arm.*/arm/ -e s/sa110/arm/)
diff --git a/examples/simple/Makefile b/examples/simple/Makefile
index 80f09193..dce7942b 100644
--- a/examples/simple/Makefile
+++ b/examples/simple/Makefile
@@ -1,5 +1,5 @@
 
-CXX=g++ -m64
+CXX=clang++ -m64
 CXXFLAGS=-Iobjs/ -O3 -Wall
 ISPC=ispc
 ISPCFLAGS=-O2 --arch=x86-64 --target=sse2
diff --git a/fail_db.txt b/fail_db.txt
index 886a4534..a9bf0031 100644
--- a/fail_db.txt
+++ b/fail_db.txt
@@ -891,3 +891,72 @@
 .\tests\uint64-min-1.ispc runfail     x86     avx1-i64x4 Windows LLVM 3.3         cl -O2 *
 .\tests\uint64-min.ispc runfail     x86     avx1-i64x4 Windows LLVM 3.3         cl -O2 *
 .\tests\reduce-min-uint64.ispc runfail     x86     avx1-i64x4 Windows LLVM 3.4         cl -O2 *
+./tests/atomics-13.ispc compfail     x86     sse4-i16x8   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/atomics-13.ispc compfail  x86-64     sse4-i16x8   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/funcptr-null-4.ispc runfail     x86     sse4-i8x16   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/funcptr-null-5.ispc runfail     x86     sse4-i8x16   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/funcptr-null-6.ispc runfail     x86     sse4-i8x16   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/atomics-13.ispc compfail     x86     sse4-i8x16   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/funcptr-null-4.ispc runfail  x86-64     sse4-i8x16   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/funcptr-null-5.ispc runfail  x86-64     sse4-i8x16   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/funcptr-null-6.ispc runfail  x86-64     sse4-i8x16   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/atomics-13.ispc compfail  x86-64     sse4-i8x16   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/ptr-assign-lhs-math-1.ispc compfail  x86-64      generic-4   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/short-vec-8.ispc compfail  x86-64      generic-4   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/test-141.ispc runfail  x86-64     generic-16   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/test-143.ispc runfail  x86-64     generic-16   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/ptr-assign-lhs-math-1.ispc compfail  x86-64     generic-16   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/avg-down-int8.ispc compfail     x86  avx1.1-i32x16   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/avg-up-int8.ispc compfail     x86  avx1.1-i32x16   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/avg-down-int8.ispc compfail  x86-64  avx1.1-i32x16   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/avg-up-int8.ispc compfail  x86-64  avx1.1-i32x16   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/test-141.ispc runfail     x86    avx2-i32x16   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/test-141.ispc runfail  x86-64    avx2-i32x16   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/reduce-equal-4.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.3 clang++3.3 -O2 *
+./tests/funcptr-null-4.ispc runfail     x86     sse4-i8x16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/funcptr-null-5.ispc runfail     x86     sse4-i8x16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/funcptr-null-6.ispc runfail     x86     sse4-i8x16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/funcptr-null-4.ispc runfail  x86-64     sse4-i8x16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/funcptr-null-5.ispc runfail  x86-64     sse4-i8x16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/funcptr-null-6.ispc runfail  x86-64     sse4-i8x16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/avg-down-int8.ispc compfail     x86    avx1-i32x16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/avg-up-int8.ispc compfail     x86    avx1-i32x16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/avg-down-int8.ispc compfail  x86-64    avx1-i32x16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/avg-up-int8.ispc compfail  x86-64    avx1-i32x16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/ptr-assign-lhs-math-1.ispc compfail  x86-64      generic-4   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/short-vec-8.ispc compfail  x86-64      generic-4   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/test-141.ispc runfail  x86-64     generic-16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/test-143.ispc runfail  x86-64     generic-16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/ptr-assign-lhs-math-1.ispc compfail  x86-64     generic-16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/avg-down-int8.ispc compfail     x86  avx1.1-i32x16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/avg-up-int8.ispc compfail     x86  avx1.1-i32x16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/avg-down-int8.ispc compfail  x86-64  avx1.1-i32x16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/avg-up-int8.ispc compfail  x86-64  avx1.1-i32x16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/atomics-varyingptr-2.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/atomics-varyingptr-3.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/atomics-varyingptr-4.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/local-atomics-11.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/local-atomics-12.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/local-atomics-13.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/local-atomics-4.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/local-atomics-5.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/local-atomics-6.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/local-atomics-7.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/local-atomics-8.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/local-atomics-swap.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/local-atomics-varyingptr-2.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/local-atomics-varyingptr-3.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/local-atomics-varyingptr-4.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/memset-varying.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/reduce-equal-1.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/reduce-equal-12.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/reduce-equal-13.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/reduce-equal-2.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/reduce-equal-3.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/reduce-equal-4.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/reduce-equal-5.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/reduce-equal-6.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/reduce-equal-7.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/reduce-equal.ispc compfail  x86-64     avx2-i32x8   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/test-141.ispc runfail     x86    avx2-i32x16   Linux LLVM 3.4 clang++3.3 -O2 *
+./tests/test-141.ispc runfail  x86-64    avx2-i32x16   Linux LLVM 3.4 clang++3.3 -O2 *
diff --git a/perf.py b/perf.py
index 0d4926e0..2b5c6edd 100755
--- a/perf.py
+++ b/perf.py
@@ -326,8 +326,8 @@ def perf(options1, args):
     ref_compiler_exists = False
     if is_windows == False:
         ispc_test = "ispc"
-        ref_compiler = "g++"
-        refc_compiler = "gcc"
+        ref_compiler = "clang++"
+        refc_compiler = "clang"
         if options.compiler != "":
             if options.compiler == "clang" or options.compiler == "clang++":
                 ref_compiler = "clang++"
@@ -335,6 +335,9 @@ def perf(options1, args):
             if options.compiler == "icc" or options.compiler == "icpc":
                 ref_compiler = "icpc"
                 refc_compiler = "icc"
+            if options.compiler == "gcc" or options.compiler == "g++":
+                ref_compiler = "g++"
+                refc_compiler = "gcc"
     else:
         ispc_test = "ispc.exe"
         ref_compiler = "cl.exe"
diff --git a/run_tests.py b/run_tests.py
index bf1b4a2b..803410b8 100755
--- a/run_tests.py
+++ b/run_tests.py
@@ -446,7 +446,7 @@ def verify():
     f = open(test_states, 'r')
     f_lines = f.readlines()
     f.close()
-    check = [["g++", "clang", "cl"],["-O0", "-O2"],["x86","x86-64"],
+    check = [["g++", "clang++", "cl"],["-O0", "-O2"],["x86","x86-64"],
              ["Linux","Windows","Mac"],["LLVM 3.1","LLVM 3.2","LLVM 3.3","LLVM head"],
              ["sse2-i32x4", "sse2-i32x8", "sse4-i32x4", "sse4-i32x8", "sse4-i16x8",
               "sse4-i8x16", "avx1-i32x8", "avx1-i32x16", "avx1-i64x4", "avx1.1-i32x8", "avx1.1-i32x16",
@@ -550,7 +550,7 @@ def run_tests(options1, args, print_version):
         if is_windows:
             options.compiler_exe = "cl.exe"
         else:
-            options.compiler_exe = "g++"
+            options.compiler_exe = "clang++"
  
     # checks the required compiler otherwise prints an error message
     PATH_dir = string.split(os.getenv("PATH"), os.pathsep)