From 1331e4eec016a295949009b4360c592401b089f7 Mon Sep 17 00:00:00 2001 From: Richard Henderson Date: Sun, 12 Sep 2021 10:49:25 -0700 Subject: [PATCH] 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. Reported-by: Richard W.M. Jones Signed-off-by: Richard Henderson --- tcg/arm/tcg-target.c.inc | 13 +++++++++---- tcg/tcg.c | 8 +++++++- 2 files changed, 16 insertions(+), 5 deletions(-) diff --git a/tcg/arm/tcg-target.c.inc b/tcg/arm/tcg-target.c.inc index 007ceee68e..34acfb522c 100644 --- a/tcg/arm/tcg-target.c.inc +++ b/tcg/arm/tcg-target.c.inc @@ -2477,8 +2477,13 @@ 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(); @@ -2497,8 +2502,8 @@ 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(); diff --git a/tcg/tcg.c b/tcg/tcg.c index 4142d42d77..ca5bcc4635 100644 --- a/tcg/tcg.c +++ b/tcg/tcg.c @@ -3060,7 +3060,13 @@ 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. */ -- 2.32.0