JIT: Handle possibility of late optimized out async calls (#121502)

If we optimize an async call away after the suspension/resumption code
has been created then the emit locations used for resumption info and
diagnostic info will not be valid. Handle this rare case by just storing
0. The value should not matter as we will never suspend here.

Suspension blocks can be removed in this case, but resumption blocks
cannot as they are referenced by the resumption switch. Ideally we would
model things so that resumption blocks could too be removed in these
cases, but that's not so simple.

Fixes issue reported in
#121298 (comment)

Author: jakobbotsch

src/coreclr/jit/codegencommon.cpp

@@ -6774,7 +6774,7 @@ void CodeGen::genReportAsyncDebugInfo()
     for (size_t i = 0; i < suspPoints->size(); i++)
     {
         emitLocation& emitLoc                   = ((emitLocation*)genAsyncResumeInfoTable->dsCont)[i];
-        (*suspPoints)[i].DiagnosticNativeOffset = emitLoc.CodeOffset(GetEmitter());
+        (*suspPoints)[i].DiagnosticNativeOffset = emitLoc.Valid() ? emitLoc.CodeOffset(GetEmitter()) : 0;
     }
 
     ICorDebugInfo::AsyncInfo asyncInfo;

src/coreclr/jit/emit.cpp

@@ -8553,14 +8553,19 @@ void emitter::emitOutputDataSec(dataSecDsc* sec, BYTE* dst)
             {
                 emitLocation* emitLoc = &((emitLocation*)dsc->dsCont)[i];
 
-                BYTE* target           = emitOffsetToPtr(emitLoc->CodeOffset(this));
+                // Async call may have been removed very late, after we have introduced suspension/resumption.
+                // In those cases just encode null.
+                BYTE* target           = emitLoc->Valid() ? emitOffsetToPtr(emitLoc->CodeOffset(this)) : nullptr;
                 aDstRW[i].Resume       = (target_size_t)(uintptr_t)emitAsyncResumeStubEntryPoint;
                 aDstRW[i].DiagnosticIP = (target_size_t)(uintptr_t)target;
                 if (emitComp->opts.compReloc)
                 {
                     uint16_t relocType = TARGET_POINTER_SIZE == 8 ? IMAGE_REL_BASED_DIR64 : IMAGE_REL_BASED_HIGHLOW;
                     emitRecordRelocation(&aDstRW[i].Resume, emitAsyncResumeStubEntryPoint, relocType);
-                    emitRecordRelocation(&aDstRW[i].DiagnosticIP, target, relocType);
+                    if (target != nullptr)
+                    {
+                        emitRecordRelocation(&aDstRW[i].DiagnosticIP, target, relocType);
+                    }
                 }
 
                 JITDUMP("  Resume=%p, FinalResumeIP=%p\n", emitAsyncResumeStubEntryPoint, (void*)target);