diff --git a/README.md b/README.md
index 480a22f..fe7f986 100644
--- a/README.md
+++ b/README.md
@@ -64,7 +64,7 @@ To install, simply do (making sure to include those `...`)
 go get github.com/SRI-CSL/gllvm/cmd/...
 ```
 This should install four binaries: `gclang`, `gclang++`, `get-bc`, and `gsanity-check`
-in the `$GOPATH/bin` directory.  
+in the `$GOPATH/bin` directory.
 
 ## Usage
 
@@ -236,6 +236,14 @@ environment variables. For more details of what's under the `gllvm` hood, try
 gsanity-check -e
 ```
 
+## Customizing the BitCode Generation (e.g. LTO)
+
+In some situations it is desirable to pass certain flags to `clang` in the step that
+produces the bitcode. This can be fulfilled by setting the
+`LLVM_BITCODE_GENERATION_FLAGS` environment variable to the desired
+flags, for example `"-flto -fwhole-program-vtables"`.
+
+
 ## License
 
 `gllvm` is released under a BSD license. See the file `LICENSE` for [details.](LICENSE)
diff --git a/shared/compiler.go b/shared/compiler.go
index 856953a..d819bfd 100644
--- a/shared/compiler.go
+++ b/shared/compiler.go
@@ -241,6 +241,8 @@ func buildObjectFile(compilerExecName string, pr parserResult, srcFile string, o
 // Tries to build the specified source file to bitcode
 func buildBitcodeFile(compilerExecName string, pr parserResult, srcFile string, bcFile string) (success bool) {
 	args := pr.CompileArgs[:]
+	//iam: 03/24/2020 extend with the LLVM_BITCODE_GENERATION_FLAGS if any.
+	args = append(args, LLVMbcGen...)
 	args = append(args, "-emit-llvm", "-c", srcFile, "-o", bcFile)
 	success, err := execCmd(compilerExecName, args, "")
 	if !success {
diff --git a/shared/constants.go b/shared/constants.go
index 38061e4..4c83e69 100644
--- a/shared/constants.go
+++ b/shared/constants.go
@@ -48,9 +48,13 @@ package shared
 //  1.2.4 June  21 2019   Random fixes (basically the same as wllvm 1.2.7)
 //
 //  1.2.5 October 23 2019  Fixes for issues #30 and #31. Plus a new branch where I can futz hygenically.
+//
+//  1.2.6 March 24 2020 Added the support for the LLVM_BITCODE_GENERATION_FLAGS environment variable.
+//                      See https://github.com/travitch/whole-program-llvm/issues/96 for details.
+//
 
-const gllvmVersion = "1.2.5"
-const gllvmReleaseDate = "October 23 2019"
+const gllvmVersion = "1.2.6"
+const gllvmReleaseDate = "March 24 2020"
 
 const osDARWIN = "darwin"
 const osLINUX = "linux"
diff --git a/shared/environment.go b/shared/environment.go
index 538ac04..6e044c6 100644
--- a/shared/environment.go
+++ b/shared/environment.go
@@ -35,6 +35,7 @@ package shared
 
 import (
 	"os"
+	"strings"
 )
 
 const (
@@ -82,6 +83,9 @@ var LLVMObjcopy string
 //LLVMLd is the path to the ld executable used to attach the bitcode on OSX.
 var LLVMLd string
 
+//LLVMbcGen is the list of args to pass to clang during the bitcode generation step.
+var LLVMbcGen []string
+
 const (
 	envpath    = "LLVM_COMPILER_PATH"
 	envcc      = "LLVM_CC_NAME"
@@ -95,14 +99,17 @@ const (
 	envld      = "GLLVM_LD"      //iam: we are deviating from wllvm here.
 	envobjcopy = "GLLVM_OBJCOPY" //iam: we are deviating from wllvm here.
 	//wllvm uses a BINUTILS_TARGET_PREFIX, which seems less general.
+	//iam: 03/24/2020 new feature to pass things like "-flto -fwhole-program-vtables"
+	// to clang during the bitcode generation step
+	envbcgen   = "LLVM_BITCODE_GENERATION_FLAGS"
 )
 
 func init() {
 	FetchEnvironment()
 }
 
-func printEnvironment() {
-	vars := []string{envpath, envcc, envcxx, envar, envlnk, envcfg, envbc, envlvl, envfile, envobjcopy, envld}
+func PrintEnvironment() {
+	vars := []string{envpath, envcc, envcxx, envar, envlnk, envcfg, envbc, envlvl, envfile, envobjcopy, envld, envbcgen}
 
 	informUser("\nLiving in this environment:\n\n")
 	for _, v := range vars {
@@ -116,7 +123,23 @@ func printEnvironment() {
 
 }
 
-// used in testing
+// also used in testing
+func ResetEnvironment() {
+	LLVMToolChainBinDir = ""
+	LLVMCCName =  ""
+	LLVMCXXName =  ""
+	LLVMARName =  ""
+	LLVMLINKName =  ""
+	LLVMConfigureOnly =  ""
+	LLVMBitcodeStorePath = ""
+	LLVMLoggingLevel = ""
+	LLVMLoggingFile = ""
+	LLVMObjcopy = ""
+	LLVMLd =  ""
+	LLVMbcGen = []string{}
+}
+
+// also used in testing
 func FetchEnvironment() {
 	LLVMToolChainBinDir = os.Getenv(envpath)
 	LLVMCCName = os.Getenv(envcc)
@@ -132,4 +155,7 @@ func FetchEnvironment() {
 
 	LLVMObjcopy = os.Getenv(envobjcopy)
 	LLVMLd = os.Getenv(envld)
+
+	LLVMbcGen = strings.Fields(os.Getenv(envbcgen))
+
 }
diff --git a/shared/sanity.go b/shared/sanity.go
index 4e79398..3e8b10b 100644
--- a/shared/sanity.go
+++ b/shared/sanity.go
@@ -108,7 +108,7 @@ func SanityCheck() {
 	informUser("\nVersion info: gsanity-check version %v\nReleased: %v\n", gllvmVersion, gllvmReleaseDate)
 
 	if sa.Environment {
-		printEnvironment()
+		PrintEnvironment()
 	}
 
 	checkLogging()
diff --git a/tests/env_and_arg_test.go b/tests/env_and_arg_test.go
index db0daca..204732b 100644
--- a/tests/env_and_arg_test.go
+++ b/tests/env_and_arg_test.go
@@ -41,6 +41,13 @@ func Test_env_and_args(t *testing.T) {
 
 	args := []string{"get-bc", "-v", "../data/hello"}
 
+	if verbose {
+		shared.PrintEnvironment()
+	}
+
+
+	shared.ResetEnvironment()
+
 	ea := shared.ParseSwitches(args)
 	if !ea.Verbose {
 		t.Errorf("ParseSwitches: -v flag not working\n")
@@ -52,6 +59,7 @@ func Test_env_and_args(t *testing.T) {
 		t.Errorf("ParseSwitches: InputFile incorrect: %v\n", ea.InputFile)
 	}
 
+	//iam: this test assumes LLVMToolChainBinDir = ""
 	checkExecutables(t, ea, "llvm-link", "llvm-ar", "ar", "clang", "clang++")
 
 	os.Setenv("LLVM_COMPILER_PATH", "/the_future_is_here")
@@ -81,5 +89,4 @@ func Test_env_and_args(t *testing.T) {
 		"ar",
 		"/the_future_is_here/clang-666",
 		"/the_future_is_here/clang++-666")
-
 }