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Re: [Qemu-devel] [PATCH 01/18] tcg: add support for 128bit vector type

From: Richard Henderson
Subject: Re: [Qemu-devel] [PATCH 01/18] tcg: add support for 128bit vector type
Date: Wed, 18 Jan 2017 10:29:14 -0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0

On 01/17/2017 01:07 AM, Kirill Batuzov wrote:
+static inline TCGv_v128 tcg_global_mem_new_v128(TCGv_ptr reg, intptr_t offset,
+                                                const char *name)
+    int idx = tcg_global_mem_new_internal(TCG_TYPE_V128, reg, offset, name);
+    return MAKE_TCGV_V128(idx);

You shouldn't allow a v128 type to be created if the host doesn't support it.

You may want to treat v128 as a pair of v64 if the host supports that. Although there's limited applicability there, since only minor hosts (MIPS, Sparc, ia64) have 64-bit-only vector extensions.

That said, treating v128 as 2 x v64 scales nicely when we add v256. Which, if we've already gone this far, is clearly how avx2 guest support should be implemented.

For hosts that have had no vector support added, you may want to represent v128 as 2 x i64, for the purpose of intermediate expansion.


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