diff options
| author | Roger Sayle <roger@nextmovesoftware.com> | 2023-05-07 07:52:15 +0100 |
|---|---|---|
| committer | Roger Sayle <roger@nextmovesoftware.com> | 2023-05-07 07:52:15 +0100 |
| commit | d8a6945c6ea22efa4d5e42fe1922d2b27953c8cd (patch) | |
| tree | f0a08495294401d1bfc14770f194d8c7dd4582b4 /gcc | |
| parent | 2c8fa77120b48b4682f423784bc7c902c9eeec0e (diff) | |
| download | gcc-d8a6945c6ea22efa4d5e42fe1922d2b27953c8cd.zip gcc-d8a6945c6ea22efa4d5e42fe1922d2b27953c8cd.tar.gz gcc-d8a6945c6ea22efa4d5e42fe1922d2b27953c8cd.tar.bz2 | |
Don't call emit_clobber in lower-subreg.cc's resolve_simple_move.
Following up on posts/reviews by Segher and Uros, there's some question
over why the middle-end's lower subreg pass emits a clobber (of a
multi-word register) into the instruction stream before emitting the
sequence of moves of the word-sized parts. This clobber interferes
with (LRA) register allocation, preventing the multi-word pseudo to
remain in the same hard registers. This patch eliminates this
(presumably superfluous) clobber and thereby improves register allocation.
A concrete example of the observed improvement is PR target/43644.
For the test case:
__int128 foo(__int128 x, __int128 y) { return x+y; }
on x86_64-pc-linux-gnu, gcc -O2 currently generates:
foo: movq %rsi, %rax
movq %rdi, %r8
movq %rax, %rdi
movq %rdx, %rax
movq %rcx, %rdx
addq %r8, %rax
adcq %rdi, %rdx
ret
with this patch, we now generate the much improved:
foo: movq %rdx, %rax
movq %rcx, %rdx
addq %rdi, %rax
adcq %rsi, %rdx
ret
2023-05-07 Roger Sayle <roger@nextmovesoftware.com>
gcc/ChangeLog
PR target/43644
* lower-subreg.cc (resolve_simple_move): Don't emit a clobber
immediately before moving a multi-word register by parts.
gcc/testsuite/ChangeLog
PR target/43644
* gcc.target/i386/pr43644.c: New test case.
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/lower-subreg.cc | 3 | ||||
| -rw-r--r-- | gcc/testsuite/gcc.target/i386/pr43644.c | 11 |
2 files changed, 11 insertions, 3 deletions
diff --git a/gcc/lower-subreg.cc b/gcc/lower-subreg.cc index 81fc5380..7c9cc3c 100644 --- a/gcc/lower-subreg.cc +++ b/gcc/lower-subreg.cc @@ -1086,9 +1086,6 @@ resolve_simple_move (rtx set, rtx_insn *insn) { unsigned int i; - if (REG_P (dest) && !HARD_REGISTER_NUM_P (REGNO (dest))) - emit_clobber (dest); - for (i = 0; i < words; ++i) { rtx t = simplify_gen_subreg_concatn (word_mode, dest, diff --git a/gcc/testsuite/gcc.target/i386/pr43644.c b/gcc/testsuite/gcc.target/i386/pr43644.c new file mode 100644 index 0000000..ffdf31c --- /dev/null +++ b/gcc/testsuite/gcc.target/i386/pr43644.c @@ -0,0 +1,11 @@ +/* { dg-do compile { target int128 } } */ +/* { dg-options "-O2" } */ + +__int128 foo(__int128 x, __int128 y) +{ + return x+y; +} + +/* { dg-final { scan-assembler-times "movq" 2 } } */ +/* { dg-final { scan-assembler-not "push" } } */ +/* { dg-final { scan-assembler-not "pop" } } */ |