[PR rtl-optimization/116420] Fix interesting block bitmap DF dataflow

The DF framework provides us a way to run dataflow problems on sub-graphs.
Naturally a bitmap of interesting blocks is passed into those routines.   At a
confluence point, the DF framework will not mark a block for re-processing if
it's not in that set of interesting blocks.

When ext-dce sets up that set of interesting blocks it's using the wrong
counter.  ie, it's using n_basic_blocks rather than last_basic_block.  If there
are holes in the block indices, some number of blocks won't get marked as
interesting.

In this case the block needing reprocessing has an index higher than
n_basic_blocks.  It never gets reprocessed and the newly found live chunks
don't propagate further up the CFG -- ultimately resulting in a pseudo
appearing to have only the low 8 bits live, when in fact the low 32 bits are
actually live.

Fixed in the obvious way, by using last_basic_block instead.

Bootstrapped and regression tested on x86_64.  Pushing to the trunk.

	PR rtl-optimization/116420
gcc/
	* ext-dce.cc (ext_dce_init): Fix loop iteration when setting up the
	interesting block for DF to analyze.

gcc/testsuite
	* gcc.dg/torture/pr116420.c: New test.

0 files changed, 0 insertions, 0 deletions