Expose TailCallKind via the LLVM C API

[etaoins]

Summary

This exposes CallInst's tail call kind via new LLVMGetTailCallKind and LLVMSetTailCallKind functions. The motivation for this is to be able to see musttail for languages that require mandatory tail calls for correctness. Today only the weaker LLVMSetTail is exposed and there is no way to set GuaranteedTailCallOpt via the C API.

[etaoins]

Thanks for the quick review! I don't have commit access so it'd be great if someone could land this for me.

[JDevlieghere]

This test seems to be failing pretty much everywhere. Can you please have a look or should we revert it?

[CodaFi]

Y’all can revert it. I’ll resubmit the patch with updated tests tomorrow.

[JDevlieghere]

In D66061#1630825, @CodaFi wrote:

Y’all can revert it. I’ll resubmit the patch with updated tests tomorrow.

Will do. Thanks!

[Jim]

llvm/trunk/lib/IR/Core.cpp

2848 ↗

(On Diff #215284)

This switch should have default case. You can add that look like.

default: 
  llvm_unreachable("Unexpected TailCallKind");

llvm/include/llvm-c/Core.h

 
 typedef unsigned LLVMAttributeIndex;
 
+typedef enum {
+  LLVMTailCallKindNone,
+  LLVMTailCallKindTail,
+  LLVMTailCallKindMustTail,
+  LLVMTailCallKindNoTail
+} LLVMTailCallKind;
+
 /**
  * @}
  */

  */
 void LLVMSetTailCall(LLVMValueRef CallInst, LLVMBool IsTailCall);
 
+/**
+ * Obtains the kind of tail call for a call instruction.
+ *
+ * This only works on llvm::CallInst instructions.
+ *
+ * @see llvm::CallInst::getTailCallKind()
+ */
+LLVMTailCallKind LLVMGetTailCallKind(LLVMValueRef CallInst);
+
+/**
+ * Set the kind of tail call for a call instruction.
+ *
+ * This only works on llvm::CallInst instructions.
+ *
+ * @see llvm::CallInst::setTailCallKind()
+ */
+void LLVMSetTailCallKind(LLVMValueRef CallInst, LLVMTailCallKind TCK);
+
 /**
  * Return the normal destination basic block.
  *

llvm/lib/IR/Core.cpp

   unwrap<CallInst>(Call)->setTailCall(isTailCall);
 }
 
+LLVMTailCallKind LLVMGetTailCallKind(LLVMValueRef Call) {
+  switch (unwrap<CallInst>(Call)->getTailCallKind()) {
+  case CallInst::TailCallKind::TCK_None:
+    return LLVMTailCallKindNone;
+  case CallInst::TailCallKind::TCK_Tail:
+    return LLVMTailCallKindTail;
+  case CallInst::TailCallKind::TCK_MustTail:
+    return LLVMTailCallKindMustTail;
+  case CallInst::TailCallKind::TCK_NoTail:
+    return LLVMTailCallKindNoTail;
+  }
+}
+
+void LLVMSetTailCallKind(LLVMValueRef Call, LLVMTailCallKind TCK) {
+  CallInst::TailCallKind kind;
+  switch (TCK) {
+  case LLVMTailCallKindNone:
+    kind = CallInst::TailCallKind::TCK_None;
+    break;
+  case LLVMTailCallKindTail:
+    kind = CallInst::TailCallKind::TCK_Tail;
+    break;
+  case LLVMTailCallKindMustTail:
+    kind = CallInst::TailCallKind::TCK_MustTail;
+    break;
+  case LLVMTailCallKindNoTail:
+    kind = CallInst::TailCallKind::TCK_NoTail;
+    break;
+  }
+
+  unwrap<CallInst>(Call)->setTailCallKind(kind);
+}
+
 /*--.. Operations on invoke instructions (only) ............................--*/
 
 LLVMBasicBlockRef LLVMGetNormalDest(LLVMValueRef Invoke) {

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

   ret i32 %merge
 
 unwind3:                                          ; preds = %landingPad
-  %8 = tail call i32 @llvm.eh.typeid.for(i8* nonnull bitcast (%C6object9ClassInfo* @C6object9Exception__ClassInfo to i8*))
+  %8 = musttail call i32 @llvm.eh.typeid.for(i8* nonnull bitcast (%C6object9ClassInfo* @C6object9Exception__ClassInfo to i8*))
   %9 = icmp eq i32 %8, %5
   br i1 %9, label %catch, label %unwind5
 
 unwind5:                                          ; preds = %unwind3
-  %10 = tail call i32 @llvm.eh.typeid.for(i8* nonnull bitcast (%C6object9ClassInfo* @C6object9Throwable__ClassInfo to i8*))
+  %10 = notail call i32 @llvm.eh.typeid.for(i8* nonnull bitcast (%C6object9ClassInfo* @C6object9Throwable__ClassInfo to i8*))
   %11 = icmp eq i32 %10, %5
   br i1 %11, label %catch, label %unwind7
 

llvm/tools/llvm-c-test/echo.cpp

           Args.push_back(CloneValue(LLVMGetOperand(Src, i)));
         LLVMValueRef Fn = CloneValue(LLVMGetCalledValue(Src));
         Dst = LLVMBuildCall(Builder, Fn, Args.data(), ArgCount, Name);
-        LLVMSetTailCall(Dst, LLVMIsTailCall(Src));
+        LLVMSetTailCallKind(Dst, LLVMGetTailCallKind(Src));
         CloneAttrs(Src, Dst);
         break;
       }