On 12/3/24 9:57 PM, Bohan Lei wrote:
This is v2 of the patch in
https://gcc.gnu.org/pipermail/gcc-patches/2024-November/669380.html.
I missed the ChangeLog entry in that version.
The commit 2c0fa3ecf70d199af18785702e9e0548fd3ab793 reuses VALUEs on sp
adjustments. We can generalize the idea and reuse VALUEs on other
registers. This can help the postreload pass find more opportunities to
simplify insns.
The following assembly code is generated from the testcase using the current
trunk compiler:
.L5:
movq %rbp, %rsi
movq %rbx, %rdi
call l
movq %rbx, %rsi
addq $4, %rbx
testl %eax, %eax
je .L6
leaq -4(%rbx), %rax
cmpq %rax, %rbp
je .L6
movq %rbx, %rdi
call as
The lea instruction is actually redundant here, as rsi contains the same
value as rbx-4 and can be used in the cmp instruction instead of rax.
With this patch, the lea instruction can be eliminated in the postreload
pass.
Bootstrapped and regtested on x86_64-pc-linux-gnu, no regressions.
gcc/ChangeLog:
* cselib.cc (REG_DERIVED_VALUE_P): New macro.
(cselib_hasher::equal): Use REG_DERIVED_VALUE_P in place of
SP_DERIVED_VALUE_P.
(autoinc_split): Ditto.
(rtx_equal_for_cselib_1): Ditto.
(cselib_hash_plus_const_int): Ditto.
(cselib_subst_to_values): Ditto.
(cselib_lookup_1): Set REG_DERIVED_VALUE_P for newly created
VALUEs for registers. Use REG_DERIVED_VALUE_P in place of
SP_DERIVED_VALUE_P for PRESERVED_VALUE_P logic.
* rtl.h (struct GTY): Mention that the volatil bit is used as
REG_DERIVED_VALUE_P in cselib.cc.
gcc/testsuite/ChangeLog:
* gcc.target/i386/cselib-1.c: New test.
---
gcc/cselib.cc | 29 ++++++++++++++----------
gcc/rtl.h | 1 +
gcc/testsuite/gcc.target/i386/cselib-1.c | 22 ++++++++++++++++++
3 files changed, 40 insertions(+), 12 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/i386/cselib-1.c
diff --git a/gcc/cselib.cc b/gcc/cselib.cc
index e6a36e892bb..43ab266c4de 100644
--- a/gcc/cselib.cc
+++ b/gcc/cselib.cc
@@ -70,6 +70,9 @@ static rtx autoinc_split (rtx, rtx *, machine_mode);
#define SP_DERIVED_VALUE_P(RTX) \
(RTL_FLAG_CHECK1 ("SP_DERIVED_VALUE_P", (RTX), VALUE)->call)
+#define REG_DERIVED_VALUE_P(RTX) \
+ (RTL_FLAG_CHECK1 ("REG_DERIVED_VALUE_P", (RTX), VALUE)->volatil)
+
Are there any cases where SP_DERIVED_VALUE_P is still used after your
proposed change? If not, then we probably should drop SP_DERIVED_VALUE_P.
Does this potentially impact debug info? That was one of the big issues
Jakub spent time on with the original patch. That's my only conceptual
concern.
Implementation wise it seems pretty straightforward.
Jeff
