Boostrapped and regtested on x86_64-redhat-linux, ppc64le-redhat-linux
and s390x-redhat-linux. I realize it might be too late for a change
like this, but it's desirable to have this in conjunction with the
https://gcc.gnu.org/pipermail/gcc-patches/2021-January/563799.html s390
regression fix, which otherwise produces unnecessary store/load
sequences in certain glibc routines, e.g. __ieee754_sqrtl. Ok for
master?
Suppose we have:
(set (reg/v:TF 63) (mem/c:TF (reg/v:DI 62)))
(set (reg:FPRX2 66) (subreg:FPRX2 (reg/v:TF 63) 0))
It is clearly profitable to propagate the first insn into the second
one and get:
(set (reg:FPRX2 66) (mem/c:FPRX2 (reg/v:DI 62)))
fwprop actually manages to perform this, but doesn't think the result is
worth it, which results in unnecessary store/load sequences on s390.
Improve the situation by classifying SUBREG -> MEM changes as
profitable.
gcc/ChangeLog:
2021-01-15 Ilya Leoshkevich <i...@linux.ibm.com>
* fwprop.c (fwprop_propagation::classify_result): Allow
(subreg (mem)) simplifications.
gcc/testsuite/ChangeLog:
2021-01-15 Ilya Leoshkevich <i...@linux.ibm.com>
* gcc.target/s390/vector/long-double-to-i64.c: Expect that
float-vector moves do *not* happen.
---
gcc/fwprop.c | 5 +++++
gcc/testsuite/gcc.target/s390/vector/long-double-to-i64.c | 3 +--
2 files changed, 6 insertions(+), 2 deletions(-)
diff --git a/gcc/fwprop.c b/gcc/fwprop.c
index eff8f7cc141..46b8ec7eccf 100644
--- a/gcc/fwprop.c
+++ b/gcc/fwprop.c
@@ -262,6 +262,11 @@ fwprop_propagation::classify_result (rtx old_rtx, rtx
new_rtx)
&& GET_MODE (new_rtx) == GET_MODE_INNER (GET_MODE (from)))
return PROFITABLE;
+ /* Allow (subreg (mem)) -> (mem) simplifications. However, do not allow
+ creating new (mem/v)s, since DCE will not remove the old ones. */
+ if (SUBREG_P (old_rtx) && MEM_P (new_rtx) && !MEM_VOLATILE_P (new_rtx))
+ return PROFITABLE;
+
return 0;
}
diff --git a/gcc/testsuite/gcc.target/s390/vector/long-double-to-i64.c
b/gcc/testsuite/gcc.target/s390/vector/long-double-to-i64.c
index 2dbbb5d1c03..8f4e377ed72 100644
--- a/gcc/testsuite/gcc.target/s390/vector/long-double-to-i64.c
+++ b/gcc/testsuite/gcc.target/s390/vector/long-double-to-i64.c
@@ -10,8 +10,7 @@ long_double_to_i64 (long double x)
return x;
}
-/* { dg-final { scan-assembler-times {\n\tvpdi\t%v\d+,%v\d+,%v\d+,1\n} 1 } } */
-/* { dg-final { scan-assembler-times {\n\tvpdi\t%v\d+,%v\d+,%v\d+,5\n} 1 } } */
+/* { dg-final { scan-assembler-not {\n\tvpdi\t} } } */
/* { dg-final { scan-assembler-times {\n\tcgxbr\t} 1 } } */
int
--
2.26.2
