llvm-c: Add LLVMDeleteInstruction to fix a test issue

[nhaehnle]

Summary

Not deleting the loose instruction with metadata associated to it causes
an assertion when the LLVMContext is destroyed. This was previously
hidden by the fact that llvm-c-test does not call LLVMShutdown. The
planned removal of ManagedStatic exposed this issue.

llvm/docs/ReleaseNotes.rst

* The following functions for creating constant expressions have been removed,
   * ``LLVMConstInsertValue``
   * ``LLVMConstUDiv``
   * ``LLVMConstExactUDiv``
   * ``LLVMConstSDiv``
   * ``LLVMConstExactSDiv``
   * ``LLVMConstURem``
   * ``LLVMConstSRem``
 
+* Add ``LLVMDeleteInstruction`` function which allows deleting instructions that
+  are not inserted into a basic block.
+
 Changes to the Go bindings
 --------------------------
 
 
 Changes to the FastISel infrastructure
 --------------------------------------
 
 * ...

llvm/include/llvm-c/Core.h

  * Obtain the instruction that occurred before this one.
  *
  * If the instruction is the first instruction in a basic block, NULL
  * will be returned.
  */
 LLVMValueRef LLVMGetPreviousInstruction(LLVMValueRef Inst);
 
 /**
- * Remove and delete an instruction.
+ * Remove an instruction.
  *
  * The instruction specified is removed from its containing building
  * block but is kept alive.
  *
  * @see llvm::Instruction::removeFromParent()
  */
 void LLVMInstructionRemoveFromParent(LLVMValueRef Inst);
 
 /**
  * Remove and delete an instruction.
  *
  * The instruction specified is removed from its containing building
  * block and then deleted.
  *
  * @see llvm::Instruction::eraseFromParent()
  */
 void LLVMInstructionEraseFromParent(LLVMValueRef Inst);
 
 /**
+ * Delete an instruction.
+ *
+ * The instruction specified is deleted. It must have previously been
+ * removed from its containing building block.
+ *
+ * @see llvm::Value::deleteValue()
+ */
+void LLVMDeleteInstruction(LLVMValueRef Inst);
+
+/**
  * Obtain the code opcode for an individual instruction.
  *
  * @see llvm::Instruction::getOpCode()
  */
 LLVMOpcode LLVMGetInstructionOpcode(LLVMValueRef Inst);
 
 /**
  * Obtain the predicate of an instruction.

llvm/lib/IR/Core.cpp

 void LLVMInstructionRemoveFromParent(LLVMValueRef Inst) {
   unwrap<Instruction>(Inst)->removeFromParent();
 }
 
 void LLVMInstructionEraseFromParent(LLVMValueRef Inst) {
   unwrap<Instruction>(Inst)->eraseFromParent();
 }
 
+void LLVMDeleteInstruction(LLVMValueRef Inst) {
+  unwrap<Instruction>(Inst)->deleteValue();
+}
+
 LLVMIntPredicate LLVMGetICmpPredicate(LLVMValueRef Inst) {
   if (ICmpInst *I = dyn_cast<ICmpInst>(unwrap(Inst)))
     return (LLVMIntPredicate)I->getPredicate();
   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(unwrap(Inst)))
     if (CE->getOpcode() == Instruction::ICmp)
       return (LLVMIntPredicate)CE->getPredicate();
   return (LLVMIntPredicate)0;
 }

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

int llvm_add_named_metadata_operand(void) {
   return 0;
 }
 
 int llvm_set_metadata(void) {
   LLVMBuilderRef b = LLVMCreateBuilder();
   LLVMValueRef values[] = { LLVMConstInt(LLVMInt32Type(), 0, 0) };
 
   // This used to trigger an assertion
-  LLVMSetMetadata(
-      LLVMBuildRetVoid(b),
-      LLVMGetMDKindID("kind", 4),
-      LLVMMDNode(values, 1));
+  LLVMValueRef ret = LLVMBuildRetVoid(b);
+  LLVMSetMetadata(ret, LLVMGetMDKindID("kind", 4), LLVMMDNode(values, 1));
 
   LLVMDisposeBuilder(b);
+  LLVMDeleteInstruction(ret);
 
   return 0;
 }