[AMDGPU][Verifier] Mark calls to entry functions as invalid in the IR verifier

For AMDGPU, calls to entry functions are invalid. Previously, due to certain
limitations, this restriction was not enforced by the IR verifier. These
limitations have now been resolved, enabling us to enforce this check.

Adding target-dependent checks directly into the IR verifier is not ideal.
However, a cleaner solution, such as a dedicated target-dependent IR verifier,
is underway (e.g., #123609). Once that
or similar code is merged, we can move this check accordingly.

Author: shiltian

llvm/include/llvm/IR/CallingConv.h

@@ -290,6 +290,27 @@ namespace CallingConv {
 
 } // end namespace CallingConv
 
+/// \return true if the calling convention allows the function to be called
+/// directly or indirectly via a call-like instruction.
+constexpr bool isCallableCC(CallingConv::ID CC) {
+  switch (CC) {
+  case CallingConv::AMDGPU_CS_Chain:
+  case CallingConv::AMDGPU_CS_ChainPreserve:
+  case CallingConv::AMDGPU_CS:
+  case CallingConv::AMDGPU_ES:
+  case CallingConv::AMDGPU_GS:
+  case CallingConv::AMDGPU_HS:
+  case CallingConv::AMDGPU_KERNEL:
+  case CallingConv::AMDGPU_LS:
+  case CallingConv::AMDGPU_PS:
+  case CallingConv::AMDGPU_VS:
+  case CallingConv::SPIR_KERNEL:
+    return false;
+  default:
+    return true;
+  }
+}
+
 } // end namespace llvm
 
 #endif // LLVM_IR_CALLINGCONV_H

llvm/lib/IR/Verifier.cpp

@@ -3596,14 +3596,9 @@ void Verifier::visitCallBase(CallBase &Call) {
     Check(Callee->getValueType() == FTy,
           "Intrinsic called with incompatible signature", Call);
 
-  // Disallow calls to functions with the amdgpu_cs_chain[_preserve] calling
-  // convention.
-  auto CC = Call.getCallingConv();
-  Check(CC != CallingConv::AMDGPU_CS_Chain &&
-            CC != CallingConv::AMDGPU_CS_ChainPreserve,
-        "Direct calls to amdgpu_cs_chain/amdgpu_cs_chain_preserve functions "
-        "not allowed. Please use the @llvm.amdgpu.cs.chain intrinsic instead.",
-        Call);
+  // Verify if the calling convention of the callee is callable.
+  Check(isCallableCC(Call.getCallingConv()),
+        "calling convention does not permit calls", Call);
 
   // Disallow passing/returning values with alignment higher than we can
   // represent.

llvm/test/CodeGen/AMDGPU/attributor-flatscratchinit.ll

@@ -849,21 +849,6 @@ define amdgpu_kernel void @calls_intrin_ascast_cc_kernel(ptr addrspace(3) %ptr)
   ret void
 }
 
-define amdgpu_kernel void @call_calls_intrin_ascast_cc_kernel(ptr addrspace(3) %ptr) {
-; GFX9-LABEL: define amdgpu_kernel void @call_calls_intrin_ascast_cc_kernel(
-; GFX9-SAME: ptr addrspace(3) [[PTR:%.*]]) #[[ATTR1]] {
-; GFX9-NEXT:    call void @calls_intrin_ascast_cc_kernel(ptr addrspace(3) [[PTR]])
-; GFX9-NEXT:    ret void
-;
-; GFX10-LABEL: define amdgpu_kernel void @call_calls_intrin_ascast_cc_kernel(
-; GFX10-SAME: ptr addrspace(3) [[PTR:%.*]]) #[[ATTR1]] {
-; GFX10-NEXT:    call void @calls_intrin_ascast_cc_kernel(ptr addrspace(3) [[PTR]])
-; GFX10-NEXT:    ret void
-;
-  call void @calls_intrin_ascast_cc_kernel(ptr addrspace(3) %ptr)
-  ret void
-}
-
 define amdgpu_kernel void @with_inline_asm() {
 ; GFX9-LABEL: define amdgpu_kernel void @with_inline_asm(
 ; GFX9-SAME: ) #[[ATTR3]] {

llvm/test/CodeGen/AMDGPU/call-to-kernel-undefined.ll

@@ -217,26 +217,3 @@ define amdgpu_cs_chain_preserve void @preallocated_cc_amdgpu_cs_chain_preserve(p
 define amdgpu_cs_chain_preserve void @inalloca_cc_amdgpu_cs_chain_preserve(ptr inalloca(i32) %ptr) {
   ret void
 }
-
-declare amdgpu_cs_chain void @amdgpu_cs_chain_call_target()
-declare amdgpu_cs_chain_preserve void @amdgpu_cs_chain_preserve_call_target()
-
-define amdgpu_cs_chain void @cant_call_amdgpu_cs_chain_functions(ptr %f) {
-  ; CHECK: Direct calls to amdgpu_cs_chain/amdgpu_cs_chain_preserve functions not allowed. Please use the @llvm.amdgpu.cs.chain intrinsic instead.
-  ; CHECK-NEXT: call amdgpu_cs_chain
-  call amdgpu_cs_chain void @amdgpu_cs_chain_call_target()
-
-  ; CHECK: Direct calls to amdgpu_cs_chain/amdgpu_cs_chain_preserve functions not allowed. Please use the @llvm.amdgpu.cs.chain intrinsic instead.
-  ; CHECK-NEXT: call amdgpu_cs_chain_preserve
-  call amdgpu_cs_chain_preserve void @amdgpu_cs_chain_preserve_call_target()
-
-  ; CHECK: Direct calls to amdgpu_cs_chain/amdgpu_cs_chain_preserve functions not allowed. Please use the @llvm.amdgpu.cs.chain intrinsic instead.
-  ; CHECK-NEXT: call amdgpu_cs_chain
-  call amdgpu_cs_chain void %f()
-
-  ; CHECK: Direct calls to amdgpu_cs_chain/amdgpu_cs_chain_preserve functions not allowed. Please use the @llvm.amdgpu.cs.chain intrinsic instead.
-  ; CHECK-NEXT: call amdgpu_cs_chain
-  call amdgpu_cs_chain_preserve void %f()
-
-  ret void
-}