[llvm] [LLVM][C API] Support Value extraction from a MetadataAsValue. (PR #105501)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-ir

Author: Tim Besard (maleadt)

<details>
<summary>Changes</summary>

It is already possible to extract the Metadata node contained in a MetadataAsValue using the C API:

```julia
julia> md = MDString("foo")
!"foo"

julia> mav = Value(LLVM.API.LLVMMetadataAsValue(context(), md));

julia> typeof(Metadata(LLVM.API.LLVMValueAsMetadata(mav)))
MDString

julia> Metadata(LLVM.API.LLVMValueAsMetadata(mav)) == md
true
```

However, `LLVMMetadataAsValue` currently does not support getting the value from a `ValueAsMetadata`:

```julia
julia> val = PointerNull(LLVM.PointerType(LLVM.Int8Type()))
i8* null

julia> vam = Metadata(LLVM.API.LLVMValueAsMetadata(val));

julia> typeof(Value(LLVM.API.LLVMMetadataAsValue(context(), vam)))
LLVM.MetadataAsValue

julia> Value(LLVM.API.LLVMMetadataAsValue(context(), vam)) == val
false
```

This PR makes `LLVMValueAsMetadata` behave like `LLVMMetadataAsValue`, returning the contained data when possible.
We've been carrying this patch for a while in LLVM.jl.

---
Full diff: https://github.com/llvm/llvm-project/pull/105501.diff


4 Files Affected:

- (modified) llvm/lib/IR/Core.cpp (+6-2) 
- (added) llvm/test/Bindings/llvm-c/vam_mav_extract.ll (+2) 
- (modified) llvm/tools/llvm-c-test/llvm-c-test.h (+1) 
- (modified) llvm/tools/llvm-c-test/main.c (+4) 
- (modified) llvm/tools/llvm-c-test/metadata.c (+19-1) 


``````````diff
diff --git a/llvm/lib/IR/Core.cpp b/llvm/lib/IR/Core.cpp
index 7665385025bd91..f4708bc18b3f8b 100644
--- a/llvm/lib/IR/Core.cpp
+++ b/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) {
diff --git a/llvm/test/Bindings/llvm-c/vam_mav_extract.ll b/llvm/test/Bindings/llvm-c/vam_mav_extract.ll
new file mode 100644
index 00000000000000..31640c460ceab7
--- /dev/null
+++ b/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
diff --git a/llvm/tools/llvm-c-test/llvm-c-test.h b/llvm/tools/llvm-c-test/llvm-c-test.h
index 1da6596cd5a8f2..44790e6a3bc8b5 100644
--- a/llvm/tools/llvm-c-test/llvm-c-test.h
+++ b/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);
diff --git a/llvm/tools/llvm-c-test/main.c b/llvm/tools/llvm-c-test/main.c
index 8be9ea06fc68da..5a1f792fb941a3 100644
--- a/llvm/tools/llvm-c-test/main.c
+++ b/llvm/tools/llvm-c-test/main.c
@@ -56,6 +56,8 @@ 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 +103,8 @@ 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")) {
diff --git a/llvm/tools/llvm-c-test/metadata.c b/llvm/tools/llvm-c-test/metadata.c
index 4fe8c00c57481b..a08ebacb49696e 100644
--- a/llvm/tools/llvm-c-test/metadata.c
+++ b/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;
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/105501