https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94256
Bug ID: 94256
Summary: Setting max-sched-region-blocks to >48 causes GCC
memory usage to explode
Product: gcc
Version: 9.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: ipa
Assignee: unassigned at gcc dot gnu.org
Reporter: sultan at kerneltoast dot com
CC: marxin at gcc dot gnu.org
Target Milestone: ---
Passing any value greater than 48 for max-sched-region-blocks causes GCC memory
usage to explode to the point of hitting the OOM killer. For example, using
"--param max-sched-region-blocks=48" causes GCC memory usage to peak at 2 GB
for my usecase. Using "--param max-sched-region-blocks=49" causes GCC memory
usage to reach the full 32 GB of my machine and causes GCC to be killed.
What is most fascinating is that, when I try to recompile GCC from source,
setting the default value for max-sched-region-blocks to a number greater than
48 in params.def causes the GCC I'm using to recompile the source to exhibit
the same issue, even though I haven't changed the max-sched-region-blocks
parameter for my host's GCC.
So, an easy way to reproduce the issue would be to:
1. Download GCC source
2. Modify the following code snippet in params.def to change the default value
of max-sched-region-blocks to 49:
Change this:
DEFPARAM(PARAM_MAX_SCHED_REGION_BLOCKS,
"max-sched-region-blocks",
"The maximum number of blocks in a region to be considered for
interblock scheduling.",
10, 0, 0)
To:
DEFPARAM(PARAM_MAX_SCHED_REGION_BLOCKS,
"max-sched-region-blocks",
"The maximum number of blocks in a region to be considered for
interblock scheduling.",
49, 0, 0)
3. Try to compile your modified GCC source using your host's GCC
4. Your host's GCC will explode in memory usage and die
