[AMDGPU][Verifier] Allow llvm.amdgcn.unreachable after cs.chain (llvm#139494)

Unreachable is transformed to llvm.amdgcn.unreachable() during exit
unification. Make sure the verifier tolerates this.

Author: perlfu

llvm/lib/IR/Verifier.cpp

@@ -6418,7 +6418,12 @@ void Verifier::visitIntrinsicCall(Intrinsic::ID ID, CallBase &Call) {
           "SGPR arguments must have the `inreg` attribute", &Call);
     Check(!Call.paramHasAttr(3, Attribute::InReg),
           "VGPR arguments must not have the `inreg` attribute", &Call);
-    Check(isa_and_present<UnreachableInst>(Call.getNextNode()),
+
+    auto *Next = Call.getNextNonDebugInstruction();
+    bool IsAMDUnreachable = Next && isa<IntrinsicInst>(Next) &&
+                            cast<IntrinsicInst>(Next)->getIntrinsicID() ==
+                                Intrinsic::amdgcn_unreachable;
+    Check(Next && (isa<UnreachableInst>(Next) || IsAMDUnreachable),
           "llvm.amdgcn.cs.chain must be followed by unreachable", &Call);
     break;
   }

llvm/test/Assembler/amdgcn-unreachable.ll

@@ -0,0 +1,32 @@
+; RUN: llvm-as < %s | llvm-dis | FileCheck %s
+
+declare amdgpu_cs_chain void @callee() nounwind
+declare void @llvm.amdgcn.cs.chain.p0.i64.i32.i32(ptr, i64, i32, i32, i32 immarg, ...)
+declare void @llvm.amdgcn.unreachable()
+declare void @llvm.dbg.value(metadata, metadata, metadata)
+
+; @llvm.amdgcn.unreachable is legal after @llvm.amdgcn.cs.chain
+; CHECK: define amdgpu_cs_chain void @test_cc_chain_unreachable(i32 %val)
+define amdgpu_cs_chain void @test_cc_chain_unreachable(i32 %val) {
+tail.block:
+  %.cond = icmp ne i32 %val, 0
+  br i1 %.cond, label %chain.block, label %UnifiedReturnBlock
+
+chain.block:
+  call void (ptr, i64, i32, i32, i32, ...) @llvm.amdgcn.cs.chain.p0.i64.i32.i32(ptr @callee, i64 -1, i32 inreg 1, i32 2, i32 1, i32 inreg 32, i32 inreg -1, ptr @callee)
+  call void @llvm.amdgcn.unreachable()
+  br label %UnifiedReturnBlock
+
+UnifiedReturnBlock:
+  ret void
+}
+
+; debug instructions should be ignored
+; CHECK: define amdgpu_cs_chain void @test_cc_chain_unreachable_debug(i32 %val)
+define amdgpu_cs_chain void @test_cc_chain_unreachable_debug(i32 %val) {
+init:
+  call void (ptr, i64, i32, i32, i32, ...) @llvm.amdgcn.cs.chain.p0.i64.i32.i32(ptr @callee, i64 -1, i32 inreg 1, i32 2, i32 1, i32 inreg 32, i32 inreg -1, ptr @callee)
+  call void @llvm.dbg.value(metadata i32 0, metadata !{}, metadata !DIExpression())
+  call void @llvm.amdgcn.unreachable()
+  ret void
+}