From 0eccd9580acf7db48d9940e64bbb3a783e867944 Mon Sep 17 00:00:00 2001
From: Katelyn Gadd <kg@luminance.org>
Date: Wed, 10 Sep 2025 11:50:41 -0700
Subject: [PATCH] Implement CEE_CKFINITE in the interpreter

---
 src/coreclr/interpreter/compiler.cpp   | 26 ++++++++++++++++++++++++++
 src/coreclr/interpreter/inc/intops.def |  3 +++
 src/coreclr/vm/interpexec.cpp          | 23 +++++++++++++++++++++++
 3 files changed, 52 insertions(+)

diff --git a/src/coreclr/interpreter/compiler.cpp b/src/coreclr/interpreter/compiler.cpp
index 26cd08599b9c3e..31d2954f82618e 100644
--- a/src/coreclr/interpreter/compiler.cpp
+++ b/src/coreclr/interpreter/compiler.cpp
@@ -4353,6 +4353,32 @@ void InterpCompiler::GenerateCode(CORINFO_METHOD_INFO* methodInfo)
                 m_ip++;
                 break;
             }
+
+            case CEE_CKFINITE:
+            {
+                CHECK_STACK(1);
+                int sVar = m_pStackPointer[-1].var;
+                StackType argType = m_pStackPointer[-1].type;
+                switch (argType)
+                {
+                    case StackTypeR4:
+                        AddIns(INTOP_CKFINITE_R4);
+                        break;
+                    case StackTypeR8:
+                        AddIns(INTOP_CKFINITE_R8);
+                        break;
+                    default:
+                        BADCODE("ckfinite operand must be R4 or R8");
+                        break;
+                }
+                m_pStackPointer--;
+                PushStackType(argType, nullptr);
+                m_pLastNewIns->SetSVar(sVar);
+                m_pLastNewIns->SetDVar(m_pStackPointer[-1].var);
+                m_ip++;
+                break;
+            }
+
             case CEE_CONV_U1:
                 CHECK_STACK(1);
                 switch (m_pStackPointer[-1].type)
diff --git a/src/coreclr/interpreter/inc/intops.def b/src/coreclr/interpreter/inc/intops.def
index f8ca4befbc9a42..99dd4cf1a6feb7 100644
--- a/src/coreclr/interpreter/inc/intops.def
+++ b/src/coreclr/interpreter/inc/intops.def
@@ -128,6 +128,9 @@ OPDEF(INTOP_NEG_R8, "neg.r8", 3, 1, 1, InterpOpNoArgs)
 OPDEF(INTOP_NOT_I4, "not.i4", 3, 1, 1, InterpOpNoArgs)
 OPDEF(INTOP_NOT_I8, "not.i8", 3, 1, 1, InterpOpNoArgs)
 
+OPDEF(INTOP_CKFINITE_R4, "ckfinite.r4", 3, 1, 1, InterpOpNoArgs)
+OPDEF(INTOP_CKFINITE_R8, "ckfinite.r8", 3, 1, 1, InterpOpNoArgs)
+
 OPDEF(INTOP_CONV_R_UN_I4, "conv.r.un.i4", 3, 1, 1, InterpOpNoArgs)
 OPDEF(INTOP_CONV_R_UN_I8, "conv.r.un.i8", 3, 1, 1, InterpOpNoArgs)
 
diff --git a/src/coreclr/vm/interpexec.cpp b/src/coreclr/vm/interpexec.cpp
index e5bd23c538a2cf..29c23d2e7b43c4 100644
--- a/src/coreclr/vm/interpexec.cpp
+++ b/src/coreclr/vm/interpexec.cpp
@@ -527,6 +527,20 @@ template <typename TResult, typename TSource> void ConvOvfHelper(int8_t *stack,
     }
 }
 
+static float CkfiniteHelper(float value)
+{
+    if (!std::isfinite(value))
+        COMPlusThrow(kArithmeticException);
+    return value;
+}
+
+static double CkfiniteHelper(double value)
+{
+    if (!std::isfinite(value))
+        COMPlusThrow(kArithmeticException);
+    return value;
+}
+
 void* DoGenericLookup(void* genericVarAsPtr, InterpGenericLookup* pLookup)
 {
     // TODO! If this becomes a performance bottleneck, we could expand out the various permutations of this
@@ -804,6 +818,15 @@ void InterpExecMethod(InterpreterFrame *pInterpreterFrame, InterpMethodContextFr
                     ip += 4;
                     break;
 
+                case INTOP_CKFINITE_R4:
+                    LOCAL_VAR(ip[1], float) = CkfiniteHelper(LOCAL_VAR(ip[2], float));
+                    ip += 3;
+                    break;
+                case INTOP_CKFINITE_R8:
+                    LOCAL_VAR(ip[1], double) = CkfiniteHelper(LOCAL_VAR(ip[2], double));
+                    ip += 3;
+                    break;
+
                 case INTOP_CONV_R_UN_I4:
                     LOCAL_VAR(ip[1], double) = (double)LOCAL_VAR(ip[2], uint32_t);
                     ip += 3;