and later versions provide support to prevent the debugged program from stopping at instructions that are predicated false. The program execution can be stopped by a software breakpoint, a hardware breakpoint, or an asynchronous signal. In the case of optimizations such as if-conversion, the predicated false instructions indicate that an alternate source path is executed. Hence, stopping the program at a predicated false instruction results in the misleading conclusion that the path corresponding to the predicated false instruction is executed. To prevent this ambiguity, HP WDB does not stop at predicated false instructions.

The predicated false instructions are equated to NOPs (No OPeration), because these instructions do not modify the processor state. The exception to this rule is the use of certain instructions, such as wtop, wexit, and frcpa, which modify the processor state even when predicated false. In such cases, the debugger stops at the instructions irrespective of the predicate value of the instructions. Assembly and low-level programmers, who require the old behavior of the debugger to stop at the instructions irrespective of the predicate value of these instructions, can explicitly turn o this feature. To explicitly turn o this feature, enter the following command at the gdb prompt:

(gdb) set no-predication-handling

The following limitations apply when debugging optimized code:

•Support for high-level loop transformations such as modulo-scheduled loops, or LNO-optimized loop nests is limited. (This limited support includes all loop optimizations that are enabled at +O3 and above, and some loop optimizations at

+O2 or -O.)

•Debug support for local aggregates and arrays is limited.

•Complete debug support for inlined subroutines is not available.

•Values that are not at the current code location will be reported as being unavailable, even if these values can be computed from some other values that are available.

•Step operations may include occasional "backwards" steps, because of the re- ordered code during optimization.

•The program stops at asynchronous signal stops even if the reported instruction is predicated false.

Complete support is available for debugging at the assembly language level. Stepping by instructions (stepi/nexti) steps as expected and reports the associated source line numbers for each instruction.

NOTE: The -ipocompilation implies the +noobjdebug option because the -ipoobject files do not store executable code or debug info.

14.30 Debugging with ARIES

The ARIES fast interpreter emulates a complete set of non-privileged PA-RISC instructions with no user intervention. During interpretation, it monitors the applications

230 HP-UX Configuration-Specific Information