openjdk/jdk · warning

*** used_mask is 0 ***

Error message

*** used_mask is 0 ***

What it means

Printed by adlc's pipeline-adventure generator (output_c.cpp, pipeline_res_mask_initializer). For each resource a pipeline class uses, it looks up the resource's mask from the pipeline's resource description; if that mask is 0 the message is printed but generation continues, and the zero mask then skews the lb/ub bit scans (the loops at minimum find lb=0..31 range only if bits set — with mask 0, 'for (lb = 0; (used_mask & (1 << lb)) == 0; lb++);' actually runs off the end of the int, undefined behavior).

Source

Thrown at src/hotspot/share/adlc/output_c.cpp:481

  static const char* pipeline_use_element    = "Pipeline_Use_Element";

  templen = 1 +
    (int)(strlen(pipeline_use_cycle_mask) + (int)strlen(pipeline_use_element) +
     (cyclemasksize * 12) + masklen + (cycledigit * 2) + 30) * element_count;

  // Allocate space for the resource list
  const size_t resource_mask_size = templen;
  char * resource_mask = new char [resource_mask_size];
  char * last_comma = nullptr;

  templen = 0;

  for (pipeclass->_resUsage.reset();
       (piperesource = (const PipeClassResourceForm*)pipeclass->_resUsage.iter()) != nullptr; ) {
    int used_mask = pipeline->_resdict[piperesource->_resource]->is_resource()->mask();

    if (!used_mask) {
      fprintf(stderr, "*** used_mask is 0 ***\n");
    }

    resources_used |= used_mask;

    uint lb, ub;

    for (lb =  0; (used_mask & (1 << lb)) == 0; lb++);
    for (ub = 31; (used_mask & (1 << ub)) == 0; ub--);

    if (lb == ub) {
      resources_used_exclusively |= used_mask;
    }

    int formatlen =
      snprintf_checked(&resource_mask[templen], resource_mask_size - templen, "  %s(0x%0*x, %*d, %*d, %s %s(",
        pipeline_use_element,
        masklen, used_mask,
        cycledigit, lb, cycledigit, ub,

View on GitHub (pinned to 88dfb74bbe)

Solutions

1. Open the .ad file's pipeline description and find the resource named in the failing pipe class's resUsage
2. Give the resource a non-empty definition, e.g. resources( INS_FLAG='0:1' ) style bit assignments, so its mask is non-zero
3. If the resource is intentionally unused, remove it from the pipe class instead of leaving a zero-mask resource
4. Re-run the build and confirm adlc stderr no longer prints '*** used_mask is 0 ***'

Example fix

// before
pipe_class myPipe(...) %{ ...; myRes; %}
// resources section declares: resource myRes; // no bits -> mask 0

// after
resources( MYRES='0:1' );
pipe_class myPipe(...) %{ ...; MYRES; %}

# Check every resource referenced by a pipe class is declared with bits in the
# pipeline description; a quick audit before building:
# 1) list resources used:  grep -oE 'resource [A-Za-z0-9_]+' <arch>.ad
# 2) list declared masks:  grep -A3 'resources\\(' <arch>.ad
# ensure every used name has a non-empty mask assignment

When it happens

Trigger: A .ad file pipeline section where a resource referenced by a pipe class (resource usage in the instruction's ins_pipe pipe class definition) has an empty/zero mask — i.e. the resource was declared with no stage list, or the resource declaration 'resource <name>' carries no bits (e.g. declared with no functional-unit assignment).

Common situations: Writing a new pipeline model for a port; declaring resources in the 'resources' block of the pipeline description but forgetting to give them stage masks / functional unit bits; referencing an undeclared-shape resource from an ins_pipe class.

Related errors

• Warning: cannot find memory opnd in instr.
• No format defined for %s
• pipeline_res_mask_initializer: semantic error: pipeline stag
• Error: Out of memory in ADLC\n
• %s: Found %d syntax error

AI-assisted analysis of openjdk/jdk@88dfb74bbe (2026-08-14). Data as JSON: /api/errors/a952c9eb62efd048. Report an issue: GitHub.