[LLVM][C API] Support Value extraction from a MetadataAsValue.

It is already possible to extract the underlying Metadata
from a ValueAsMetadata.

Author: maleadt

llvm/lib/IR/Core.cpp

@@ -1328,8 +1328,12 @@ LLVMValueRef LLVMMDNode(LLVMValueRef *Vals, unsigned Count) {
   return LLVMMDNodeInContext(LLVMGetGlobalContext(), Vals, Count);
 }
 
-LLVMValueRef LLVMMetadataAsValue(LLVMContextRef C, LLVMMetadataRef MD) {
-  return wrap(MetadataAsValue::get(*unwrap(C), unwrap(MD)));
+LLVMValueRef LLVMMetadataAsValue(LLVMContextRef C, LLVMMetadataRef Metadata) {
+  auto *MD = unwrap(Metadata);
+  if (auto *VAM = dyn_cast<ValueAsMetadata>(MD))
+    return wrap(VAM->getValue());
+  else
+    return wrap(MetadataAsValue::get(*unwrap(C), MD));
 }
 
 LLVMMetadataRef LLVMValueAsMetadata(LLVMValueRef Val) {

llvm/test/Bindings/llvm-c/vam_mav_extract.ll

@@ -0,0 +1,2 @@
+; RUN: llvm-c-test --vam-mav-extract < /dev/null
+; This used to trigger an assertion

llvm/tools/llvm-c-test/llvm-c-test.h

@@ -45,6 +45,7 @@ int llvm_add_named_metadata_operand(void);
 int llvm_set_metadata(void);
 int llvm_replace_md_operand(void);
 int llvm_is_a_value_as_metadata(void);
+int llvm_vam_mav_extract(void);
 
 // object.c
 int llvm_object_list_sections(void);

llvm/tools/llvm-c-test/main.c

@@ -56,6 +56,9 @@ static void print_usage(void) {
   fprintf(stderr, "  * --is-a-value-as-metadata\n");
   fprintf(stderr,
           "    Run test for checking if LLVMValueRef is a ValueAsMetadata\n");
+  fprintf(stderr, "  * --vam-mav-extract\n");
+  fprintf(stderr, "    Run test for extracting data from ValueAsMetadata and "
+                  "MetadataAsValue\n");
   fprintf(stderr, "  * --echo\n");
   fprintf(stderr, "    Read bitcode file from stdin - print it back out\n\n");
   fprintf(stderr, "  * --test-diagnostic-handler\n");
@@ -101,6 +104,8 @@ int main(int argc, char **argv) {
     return llvm_replace_md_operand();
   } else if (argc == 2 && !strcmp(argv[1], "--is-a-value-as-metadata")) {
     return llvm_is_a_value_as_metadata();
+  } else if (argc == 2 && !strcmp(argv[1], "--vam-mav-extract")) {
+    return llvm_vam_mav_extract();
   } else if (argc == 2 && !strcmp(argv[1], "--test-function-attributes")) {
     return llvm_test_function_attributes();
   } else if (argc == 2 && !strcmp(argv[1], "--test-callsite-attributes")) {

llvm/tools/llvm-c-test/metadata.c

@@ -80,7 +80,7 @@ int llvm_is_a_value_as_metadata(void) {
   LLVMContextRef Context = LLVMGetModuleContext(M);
 
   {
-    LLVMValueRef Int = LLVMConstInt(LLVMInt32Type(), 0, 0);
+    LLVMValueRef Int = LLVMConstInt(LLVMInt32TypeInContext(Context), 0, 0);
     LLVMValueRef NodeMD = LLVMMDNode(&Int, 1);
     assert(LLVMIsAValueAsMetadata(NodeMD) == NodeMD);
     (void)NodeMD;
@@ -98,3 +98,21 @@ int llvm_is_a_value_as_metadata(void) {
 
   return 0;
 }
+
+int llvm_vam_mav_extract(void) {
+  LLVMModuleRef M = LLVMModuleCreateWithName("Mod");
+  LLVMContextRef Context = LLVMGetModuleContext(M);
+
+  LLVMValueRef Val = LLVMConstInt(LLVMInt32TypeInContext(Context), 0, 0);
+  LLVMMetadataRef MD = LLVMMDStringInContext2(Context, "foo", 3);
+
+  // construction
+  LLVMValueRef MAV = LLVMMetadataAsValue(Context, MD);
+  LLVMMetadataRef VAM = LLVMValueAsMetadata(Val);
+
+  // extraction
+  assert(LLVMMetadataAsValue(Context, VAM) == Val);
+  assert(LLVMValueAsMetadata(MAV) == MD);
+
+  return 0;
+}