[llvm-extract] Add -keep-const-init commandline option

Summary:
This adds -keep-const-init option to llvm-extract which preserves initializers of
used global constants.

For example:

```
$ cat a.ll
@g = constant i32 0
define i32 @f() {
  %v = load i32, i32* @g
  ret i32 %v
}

$ llvm-extract --func=f a.ll -S -o -
@g = external constant i32
define i32 @f() { .. }

$ llvm-extract --func=f a.ll -keep-const-init -S -o -
@g = constant i32 0
define i32 @f() { .. }
```

This option is useful in checking whether a function that uses a constant global is optimized correctly.

Reviewers: jsji, MaskRay, david2050

Reviewed By: MaskRay

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73833

1 files changed, 5 insertions, 1 deletions

diff --git a/llvm/tools/llvm-extract/llvm-extract.cpp b/llvm/tools/llvm-extract/llvm-extract.cpp
index dddc0d9..ac70b5f 100644
--- a/llvm/tools/llvm-extract/llvm-extract.cpp
+++ b/llvm/tools/llvm-extract/llvm-extract.cpp
@@ -53,6 +53,10 @@ static cl::opt<bool> DeleteFn("delete",
                               cl::desc("Delete specified Globals from Module"),
                               cl::cat(ExtractCat));
 
+static cl::opt<bool> KeepConstInit("keep-const-init",
+                              cl::desc("Keep initializers of constants"),
+                              cl::cat(ExtractCat));
+
 static cl::opt<bool>
     Recursive("recursive", cl::desc("Recursively extract all called functions"),
               cl::cat(ExtractCat));
@@ -333,7 +337,7 @@ int main(int argc, char **argv) {
   {
     std::vector<GlobalValue *> Gvs(GVs.begin(), GVs.end());
     legacy::PassManager Extract;
-    Extract.add(createGVExtractionPass(Gvs, DeleteFn));
+    Extract.add(createGVExtractionPass(Gvs, DeleteFn, KeepConstInit));
     Extract.run(*M);
 
     // Now that we have all the GVs we want, mark the module as fully