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https://issues.apache.org/jira/browse/IMPALA-6380?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18046369#comment-18046369
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Raghav Jindal commented on IMPALA-6380:
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[~kwho] Is this task still open ?
> Replace FunctionContext::IsArgConstant(int i) with constant during codegen
> --------------------------------------------------------------------------
>
> Key: IMPALA-6380
> URL: https://issues.apache.org/jira/browse/IMPALA-6380
> Project: IMPALA
> Issue Type: Improvement
> Components: Backend
> Affects Versions: Impala 2.12.0
> Reporter: Michael Ho
> Priority: Minor
> Labels: codegen, newbie
>
> There are few places in the string related built-in functions which check
> whether the input argument is constant per row:
> {noformat}
> TimestampVal TimestampFunctions::ToTimestamp(FunctionContext* context,
> const StringVal& date, const StringVal& fmt) {
> if (fmt.is_null || fmt.len == 0) {
> TimestampFunctions::ReportBadFormat(context, fmt, false);
> return TimestampVal::null();
> }
> if (date.is_null || date.len == 0) return TimestampVal::null();
> void* state = context->GetFunctionState(FunctionContext::THREAD_LOCAL);
> DateTimeFormatContext* dt_ctx =
> reinterpret_cast<DateTimeFormatContext*>(state);
> if (!context->IsArgConstant(1)) {
> dt_ctx->Reset(reinterpret_cast<const char*>(fmt.ptr), fmt.len);
> if (!TimestampParser::ParseFormatTokens(dt_ctx)) {
> ReportBadFormat(context, fmt, false);
> return TimestampVal::null();
> }
> }
> const TimestampValue& tv = TimestampValue::Parse(
> reinterpret_cast<const char*>(date.ptr), date.len, *dt_ctx);
> TimestampVal tv_val;
> tv.ToTimestampVal(&tv_val);
> return tv_val;
> }
> {noformat}
> {noformat}
> StringVal StringFunctions::BTrimString(FunctionContext* ctx,
> const StringVal& str, const StringVal& chars_to_trim) {
> if (str.is_null) return StringVal::null();
> bitset<256>* unique_chars = reinterpret_cast<bitset<256>*>(
> ctx->GetFunctionState(FunctionContext::THREAD_LOCAL));
> // When 'chars_to_trim' is unique for each element (e.g. when
> 'chars_to_trim'
> // is each element of a table column), we need to prepare a bitset of unique
> // characters here instead of using the bitset from function context.
> if (!ctx->IsArgConstant(1)) {
> unique_chars->reset();
> DCHECK(chars_to_trim.len != 0 || chars_to_trim.is_null);
> for (int32_t i = 0; i < chars_to_trim.len; ++i) {
> unique_chars->set(static_cast<int>(chars_to_trim.ptr[i]), true);
> }
> }
> ...
> ...
> {noformat}
> it seems generally useful to extend {{FunctionContextImpl::GetConstFnAttr()}}
> to also return whether the i-th argument to a UDF is constant or not and then
> replace these calls with constants during codegen.
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