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target/104581 - compile-time regression in mode-switching 

The x86 backend piggy-backs on mode-switching for insertion of
vzeroupper.  A recent improvement there was implemented in a way
to walk possibly the whole basic-block for all DF reg def definitions
in its mode_needed hook which is called for each instruction in
a basic-block during mode-switching local analysis.

The following mostly reverts this improvement.  It needs to be
re-done in a way more consistent with a local dataflow which
probably means making targets aware of the state of the local
dataflow analysis.

2022-02-17  Richard Biener  <rguenther@suse.de>

	PR target/104581
	* config/i386/i386.cc (ix86_avx_u128_mode_source): Remove.
	(ix86_avx_u128_mode_needed): Return AVX_U128_DIRTY instead
	of calling ix86_avx_u128_mode_source which would eventually
	have returned AVX_U128_ANY in some very special case.

	* gcc.target/i386/pr101456-1.c: XFAIL.
This commit is contained in:
Richard Biener 2022-02-17 14:40:16 +01:00
parent 422d1d378e
commit fe79d652c9
2 changed files with 5 additions and 76 deletions
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78
gcc/config/i386/i386.cc
View File

@ -14377,80 +14377,12 @@ ix86_check_avx_upper_register (const_rtx exp)
static void
ix86_check_avx_upper_stores (rtx dest, const_rtx, void *data)
{
if (ix86_check_avx_upper_register (dest))
{
if (ix86_check_avx_upper_register (dest))
{
bool *used = (bool *) data;
*used = true;
}
}
/* For YMM/ZMM store or YMM/ZMM extract. Return mode for the source
operand of SRC DEFs in the same basic block before INSN. */
static int
ix86_avx_u128_mode_source (rtx_insn *insn, const_rtx src)
{
basic_block bb = BLOCK_FOR_INSN (insn);
rtx_insn *end = BB_END (bb);
/* Return AVX_U128_DIRTY if there is no DEF in the same basic
block. */
int status = AVX_U128_DIRTY;
for (df_ref def = DF_REG_DEF_CHAIN (REGNO (src));
def; def = DF_REF_NEXT_REG (def))
if (DF_REF_BB (def) == bb)
{
/* Ignore DEF from different basic blocks. */
rtx_insn *def_insn = DF_REF_INSN (def);
/* Check if DEF_INSN is before INSN. */
rtx_insn *next;
for (next = NEXT_INSN (def_insn);
next != nullptr && next != end && next != insn;
next = NEXT_INSN (next))
;
/* Skip if DEF_INSN isn't before INSN. */
if (next != insn)
continue;
/* Return AVX_U128_DIRTY if the source operand of DEF_INSN
isn't constant zero. */
if (CALL_P (def_insn))
{
bool avx_upper_reg_found = false;
note_stores (def_insn,
ix86_check_avx_upper_stores,
&avx_upper_reg_found);
/* Return AVX_U128_DIRTY if call returns AVX. */
if (avx_upper_reg_found)
return AVX_U128_DIRTY;
continue;
}
rtx set = single_set (def_insn);
if (!set)
return AVX_U128_DIRTY;
rtx dest = SET_DEST (set);
/* Skip if DEF_INSN is not an AVX load. Return AVX_U128_DIRTY
if the source operand isn't constant zero. */
if (ix86_check_avx_upper_register (dest)
&& standard_sse_constant_p (SET_SRC (set),
GET_MODE (dest)) != 1)
return AVX_U128_DIRTY;
/* We get here only if all AVX loads are from constant zero. */
status = AVX_U128_ANY;
}
return status;
}
/* Return needed mode for entity in optimize_mode_switching pass. */
@ -14520,11 +14452,7 @@ ix86_avx_u128_mode_needed (rtx_insn *insn)
{
FOR_EACH_SUBRTX (iter, array, src, NONCONST)
if (ix86_check_avx_upper_register (*iter))
{
int status = ix86_avx_u128_mode_source (insn, *iter);
if (status == AVX_U128_DIRTY)
return status;
}
return AVX_U128_DIRTY;
}
/* This isn't YMM/ZMM load/store. */

3
gcc/testsuite/gcc.target/i386/pr101456-1.c
View File

@ -30,4 +30,5 @@ foo3 (void)
bar ();
}
/* { dg-final { scan-assembler-not "vzeroupper" } } */
/* See PR104581 for the XFAIL reason. */
/* { dg-final { scan-assembler-not "vzeroupper" { xfail *-*-* } } } */