On Tue, Feb 17, 2026 at 8:31 PM Uros Bizjak <[email protected]> wrote:
>
> On Tue, Feb 17, 2026 at 6:53 AM H.J. Lu <[email protected]> wrote:
> >
> > Since the same hard register may be used for both non-stack access and
> > stack access, change ix86_find_max_used_stack_alignment to update stack
> > alignment only if the hard register in the set basic block, which
> > dominates the use basic block, accesses stack.
>
> This sentence is really hard to parse. I guess it is more clear to say:
>
> "The same hard register may be used for both stack and non-stack
> accesses. Update ix86_find_max_used_stack_alignment to adjust stack
> alignment only when a hard register used for a stack access is defined
> in a basic block that dominates the block where it is used."
Fixed.
> +/* Return true if hard register REGNO set in the basic block, which
> + dominates basic block BB, accesses stack. */
> +
>
> Return true if the hard register REGNO used for a stack access is
> defined in a basic block that dominates the block where it is used.
Fixed.
> + if (TEST_HARD_REG_BIT (hard_stack_slot_access, regno)
> + || ix86_access_stack_p (regno, BLOCK_FOR_INSN (insn),
> + set_up_by_prologue, prologue_used))
> + {
> + /* Update stack alignment if REGNO accesses stack. */
>
> Update stack alignment if REGNO is used for stack access.
Fixed.
> + note_stores (insn, ix86_update_stack_alignment,
> + &data);
>
> This can be in one line.
Fixed.
> Just a faint rubber-stamp LGTM otherwise - you are the expert in this area.
>
> Thanks,
> Uros.
This is what I checked in.
Thanks.
--
H.J.
From b54533a28632482e91d7dfbbc47c75fb6d5e78bb Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <[email protected]>
Date: Tue, 17 Feb 2026 09:51:58 +0800
Subject: [PATCH] x86: Update stack alignment only if stack is used
The same hard register may be used for both stack and non-stack accesses.
Update ix86_find_max_used_stack_alignment to adjust stack alignment only
when a hard register used for a stack access is defined in a basic block
that dominates the block where it is used.
gcc/
PR target/124098
* config/i386/i386.cc (ix86_access_stack_p): New.
(ix86_find_max_used_stack_alignment): Update stack alignment only
if stack is used.
gcc/testsuite/
PR target/124098
* gcc.target/i386/pr124098.c: New test.
Signed-off-by: H.J. Lu <[email protected]>
---
gcc/config/i386/i386.cc | 49 +++++++++++++++++++++++-
gcc/testsuite/gcc.target/i386/pr124098.c | 12 ++++++
2 files changed, 59 insertions(+), 2 deletions(-)
create mode 100644 gcc/testsuite/gcc.target/i386/pr124098.c
diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index 8a54648337d..42a73d65fb1 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -8711,6 +8711,37 @@ ix86_find_all_reg_uses (HARD_REG_SET ®set,
}
}
+/* Return true if the hard register REGNO used for a stack access is
+ defined in a basic block that dominates the block where it is used. */
+
+static bool
+ix86_access_stack_p (unsigned int regno, basic_block bb,
+ HARD_REG_SET &set_up_by_prologue,
+ HARD_REG_SET &prologue_used)
+{
+ /* Get all BBs which set REGNO and dominate the current BB from all
+ DEFs of REGNO. */
+ for (df_ref def = DF_REG_DEF_CHAIN (regno);
+ def;
+ def = DF_REF_NEXT_REG (def))
+ if (!DF_REF_IS_ARTIFICIAL (def)
+ && !DF_REF_FLAGS_IS_SET (def, DF_REF_MAY_CLOBBER)
+ && !DF_REF_FLAGS_IS_SET (def, DF_REF_MUST_CLOBBER))
+ {
+ basic_block set_bb = DF_REF_BB (def);
+ if (dominated_by_p (CDI_DOMINATORS, bb, set_bb))
+ {
+ rtx_insn *insn = DF_REF_INSN (def);
+ /* Return true if INSN requires stack. */
+ if (requires_stack_frame_p (insn, prologue_used,
+ set_up_by_prologue))
+ return true;
+ }
+ }
+
+ return false;
+}
+
/* Set stack_frame_required to false if stack frame isn't required.
Update STACK_ALIGNMENT to the largest alignment, in bits, of stack
slot used if stack frame is required and CHECK_STACK_SLOT is true. */
@@ -8771,6 +8802,10 @@ ix86_find_max_used_stack_alignment (unsigned int &stack_alignment,
bitmap_set_bit (worklist, HARD_FRAME_POINTER_REGNUM);
}
+ HARD_REG_SET hard_stack_slot_access = stack_slot_access;
+
+ calculate_dominance_info (CDI_DOMINATORS);
+
unsigned int regno;
do
@@ -8798,9 +8833,19 @@ ix86_find_max_used_stack_alignment (unsigned int &stack_alignment,
if (!NONJUMP_INSN_P (insn))
continue;
- data.reg = DF_REF_REG (ref);
- note_stores (insn, ix86_update_stack_alignment, &data);
+ if (TEST_HARD_REG_BIT (hard_stack_slot_access, regno)
+ || ix86_access_stack_p (regno, BLOCK_FOR_INSN (insn),
+ set_up_by_prologue, prologue_used))
+ {
+ /* Update stack alignment if REGNO is used for stack
+ access. */
+ data.reg = DF_REF_REG (ref);
+ note_stores (insn, ix86_update_stack_alignment, &data);
+ continue;
+ }
}
+
+ free_dominance_info (CDI_DOMINATORS);
}
/* Finalize stack_realign_needed and frame_pointer_needed flags, which
diff --git a/gcc/testsuite/gcc.target/i386/pr124098.c b/gcc/testsuite/gcc.target/i386/pr124098.c
new file mode 100644
index 00000000000..0b552acc6b3
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr124098.c
@@ -0,0 +1,12 @@
+/* { dg-do compile { target int128 } } */
+/* { dg-options "-O2 -mno-avx512f -mavx2" } */
+
+char c, d;
+_BitInt(2048) b;
+
+void
+foo (__int128, _BitInt(1024) a)
+{
+ b *= 0;
+ c %= (char)(a ?: d);
+}
--
2.53.0
