[LLVM-C] Allow LLVMGetVolatile to work with any kind of Instruction (llvm#163060)

Allow LLVMGetVolatile() to work with any kind of Instruction, rather
than only memory instructions that accept a volatile flag. For
instructions that can never be volatile, the function now return false
instead of asserting. This matches the behavior of
`Instruction::isVolatile()` in the C++ API.

Author: AMS21

llvm/docs/ReleaseNotes.md

@@ -147,6 +147,7 @@ Changes to the C API
 --------------------
 
 * Add `LLVMGetOrInsertFunction` to get or insert a function, replacing the combination of `LLVMGetNamedFunction` and `LLVMAddFunction`.
+* Allow `LLVMGetVolatile` to work with any kind of Instruction.
 
 Changes to the CodeGen infrastructure
 -------------------------------------

llvm/include/llvm-c/Core.h

@@ -4757,7 +4757,7 @@ LLVM_C_ABI LLVMValueRef LLVMBuildGlobalString(LLVMBuilderRef B, const char *Str,
 LLVM_C_ABI LLVMValueRef LLVMBuildGlobalStringPtr(LLVMBuilderRef B,
                                                  const char *Str,
                                                  const char *Name);
-LLVM_C_ABI LLVMBool LLVMGetVolatile(LLVMValueRef MemoryAccessInst);
+LLVM_C_ABI LLVMBool LLVMGetVolatile(LLVMValueRef Inst);
 LLVM_C_ABI void LLVMSetVolatile(LLVMValueRef MemoryAccessInst,
                                 LLVMBool IsVolatile);
 LLVM_C_ABI LLVMBool LLVMGetWeak(LLVMValueRef CmpXchgInst);

llvm/lib/IR/Core.cpp

@@ -4098,15 +4098,8 @@ LLVMValueRef LLVMBuildGlobalStringPtr(LLVMBuilderRef B, const char *Str,
   return wrap(unwrap(B)->CreateGlobalString(Str, Name));
 }
 
-LLVMBool LLVMGetVolatile(LLVMValueRef MemAccessInst) {
-  Value *P = unwrap(MemAccessInst);
-  if (LoadInst *LI = dyn_cast<LoadInst>(P))
-    return LI->isVolatile();
-  if (StoreInst *SI = dyn_cast<StoreInst>(P))
-    return SI->isVolatile();
-  if (AtomicRMWInst *AI = dyn_cast<AtomicRMWInst>(P))
-    return AI->isVolatile();
-  return cast<AtomicCmpXchgInst>(P)->isVolatile();
+LLVMBool LLVMGetVolatile(LLVMValueRef Inst) {
+  return cast<Instruction>(unwrap(Inst))->isVolatile();
 }
 
 void LLVMSetVolatile(LLVMValueRef MemAccessInst, LLVMBool isVolatile) {