public inbox for gcc-cvs@sourceware.org
help / color / mirror / Atom feed
* [gcc(refs/users/meissner/heads/dmf007)] Bump up precision size to 11 bits.
@ 2023-02-01 3:09 Michael Meissner
0 siblings, 0 replies; only message in thread
From: Michael Meissner @ 2023-02-01 3:09 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:79fbfd2c5bc64e7e705f86cac8da29c04187000d
commit 79fbfd2c5bc64e7e705f86cac8da29c04187000d
Author: Michael Meissner <meissner@linux.ibm.com>
Date: Tue Jan 31 22:08:53 2023 -0500
Bump up precision size to 11 bits.
The new __dmr type that is being added as a possible future PowerPC instruction
set bumps into a structure field size issue. The size of the __dmr type is 1024 bits.
The precision field in tree_type_common is currently 10 bits, so if you store
1,024 into field, you get a 0 back. When you get 0 in the precision field, the
ccp pass passes this 0 to sext_hwi in hwint.h. That function in turn generates
a shift that is equal to the host wide int bit size, which is undefined as
machine dependent for shifting in C/C++.
int shift = HOST_BITS_PER_WIDE_INT - prec;
return ((HOST_WIDE_INT) ((unsigned HOST_WIDE_INT) src << shift)) >> shift;
It turns out the x86_64 where I first did my tests returns the original input
before the two shifts, while the PowerPC always returns 0. In the ccp pass, the
original input is -1, and so it worked. When I did the runs on the PowerPC, the
result was 0, which ultimately led to the failure.
2023-01-31 Michael Meissner <meissner@linux.ibm.com>
gcc/
* hwint.h (sext_hwi): Add assertion against precision 0.
* tree-core.h (tree_type_common): Bump up precision field by 1 bit, and
reduce contains_placeholder_bits to 1 bit.
Diff:
---
gcc/hwint.h | 1 +
gcc/tree-core.h | 4 ++--
2 files changed, 3 insertions(+), 2 deletions(-)
diff --git a/gcc/hwint.h b/gcc/hwint.h
index e31aa006fa4..ba92efbfc25 100644
--- a/gcc/hwint.h
+++ b/gcc/hwint.h
@@ -277,6 +277,7 @@ ctz_or_zero (unsigned HOST_WIDE_INT x)
static inline HOST_WIDE_INT
sext_hwi (HOST_WIDE_INT src, unsigned int prec)
{
+ gcc_checking_assert (prec != 0);
if (prec == HOST_BITS_PER_WIDE_INT)
return src;
else
diff --git a/gcc/tree-core.h b/gcc/tree-core.h
index 8124a1328d4..e27eb1eb87f 100644
--- a/gcc/tree-core.h
+++ b/gcc/tree-core.h
@@ -1686,12 +1686,12 @@ struct GTY(()) tree_type_common {
tree attributes;
unsigned int uid;
- unsigned int precision : 10;
+ unsigned int precision : 11;
unsigned no_force_blk_flag : 1;
unsigned needs_constructing_flag : 1;
unsigned transparent_aggr_flag : 1;
unsigned restrict_flag : 1;
- unsigned contains_placeholder_bits : 2;
+ unsigned contains_placeholder_bits : 1;
ENUM_BITFIELD(machine_mode) mode : 8;
^ permalink raw reply [flat|nested] only message in thread
only message in thread, other threads:[~2023-02-01 3:09 UTC | newest]
Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-02-01 3:09 [gcc(refs/users/meissner/heads/dmf007)] Bump up precision size to 11 bits Michael Meissner
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).