https://gcc.gnu.org/g:16ec69161c3a3537076cea467e3622bb4a2550d0
commit 16ec69161c3a3537076cea467e3622bb4a2550d0
Author: Jeff Law <j...@ventanamicro.com>
Date: Sun Jul 21 07:36:37 2024 -0600
[PR rtl-optimization/115877] Fix livein computation for ext-dce
So I'm not yet sure how I'm going to break everything down, but this is easy
enough to break out as 1/N of ext-dce fixes/improvements.
When handling uses in an insn, we first determine what bits are set in the
destination which is represented in DST_MASK. Then we use that to refine
what
bits are live in the source operands.
In the source operand handling section we *modify* DST_MASK if the source
operand is a SUBREG (ugh!). So if the first operand is a SUBREG, then we
can
incorrectly compute which bit groups are live in the second operand,
especially
if it is a SUBREG as well.
This was seen when testing a larger set of patches on the rl78 port
(builtin-arith-overflow-p-7 & pr71631 execution failures), so no new test
for
this bugfix.
Run through my tester (in conjunction with other ext-dce changes) on the
various cross targets. Run individually through a bootstrap and regression
test cycle on x86_64 as well.
Pushing to the trunk.
PR rtl-optimization/115877
gcc/
* ext-dce.cc (ext_dce_process_uses): Restore the value of DST_MASK
for reach operand.
(cherry picked from commit 91e468b72dafc9dcd5dcf7915f1d0ef172264d53)
Diff:
---
gcc/ext-dce.cc | 2 ++
1 file changed, 2 insertions(+)
diff --git a/gcc/ext-dce.cc b/gcc/ext-dce.cc
index 7270de2a3bf..d431f8ac12d 100644
--- a/gcc/ext-dce.cc
+++ b/gcc/ext-dce.cc
@@ -591,8 +591,10 @@ ext_dce_process_uses (rtx_insn *insn, rtx obj, bitmap
live_tmp)
making things live. Breaking from this loop will cause
the iterator to work on sub-rtxs, so it is safe to break
if we see something we don't know how to handle. */
+ unsigned HOST_WIDE_INT save_mask = dst_mask;
for (;;)
{
+ dst_mask = save_mask;
/* Strip an outer paradoxical subreg. The bits outside
the inner mode are don't cares. So we can just strip
and process the inner object. */
