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tcg/arm: Reduce vector alignment requirement for NEON 

With arm32, the ABI gives us 8-byte alignment for the stack.
While it's possible to realign the stack to provide 16-byte alignment,
it's far easier to simply not encode 16-byte alignment in the
VLD1 and VST1 instructions that we emit.

Remove the assertion in temp_allocate_frame, limit natural alignment
to the provided stack alignment, and add a comment.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1999878
Reported-by: Richard W.M. Jones <rjones@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210912174925.200132-1-richard.henderson@linaro.org>
Message-Id: <20211206191335.230683-2-richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2021-09-12 10:49:25 -07:00
parent 7635eff971
commit b9537d5904
2 changed files with 16 additions and 5 deletions
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13
tcg/arm/tcg-target.c.inc
View File

@ -2523,8 +2523,13 @@ static void tcg_out_ld(TCGContext *s, TCGType type, TCGReg arg,
tcg_out_vldst(s, INSN_VLD1 | 0x7d0, arg, arg1, arg2);
return;
case TCG_TYPE_V128:
/* regs 2; size 8; align 16 */
tcg_out_vldst(s, INSN_VLD1 | 0xae0, arg, arg1, arg2);
/*
* We have only 8-byte alignment for the stack per the ABI.
* Rather than dynamically re-align the stack, it's easier
* to simply not request alignment beyond that. So:
* regs 2; size 8; align 8
*/
tcg_out_vldst(s, INSN_VLD1 | 0xad0, arg, arg1, arg2);
return;
default:
g_assert_not_reached();
@ -2543,8 +2548,8 @@ static void tcg_out_st(TCGContext *s, TCGType type, TCGReg arg,
tcg_out_vldst(s, INSN_VST1 | 0x7d0, arg, arg1, arg2);
return;
case TCG_TYPE_V128:
/* regs 2; size 8; align 16 */
tcg_out_vldst(s, INSN_VST1 | 0xae0, arg, arg1, arg2);
/* See tcg_out_ld re alignment: regs 2; size 8; align 8 */
tcg_out_vldst(s, INSN_VST1 | 0xad0, arg, arg1, arg2);
return;
default:
g_assert_not_reached();

8
tcg/tcg.c
View File

@ -3061,7 +3061,13 @@ static void temp_allocate_frame(TCGContext *s, TCGTemp *ts)
g_assert_not_reached();
}
assert(align <= TCG_TARGET_STACK_ALIGN);
/*
* Assume the stack is sufficiently aligned.
* This affects e.g. ARM NEON, where we have 8 byte stack alignment
* and do not require 16 byte vector alignment. This seems slightly
* easier than fully parameterizing the above switch statement.
*/
align = MIN(TCG_TARGET_STACK_ALIGN, align);
off = ROUND_UP(s->current_frame_offset, align);
/* If we've exhausted the stack frame, restart with a smaller TB. */