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From: | Philippe Mathieu-Daudé |
Subject: | Re: [Qemu-devel] [PATCH 1/8] coccinelle: add a script to optimize tcg op using tcg_gen_extract() |
Date: | Wed, 10 May 2017 18:27:47 -0300 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 |
On 05/10/2017 05:19 PM, Richard Henderson wrote:
On 05/10/2017 01:05 PM, Philippe Mathieu-Daudé wrote:+-tcg_gen_shri_tl(ret, arg, ofs); +-tcg_gen_andi_tl(ret, ret, len); ++tcg_gen_extract_tl(ret, arg, ofs, len);You can't simply copy the and mask to the extract length. You need to verify it's all low bits and convert that to a count of the low bits. E.g. 0xff -> 8.
Hey Richard, this pattern can be applied as long as len << ofs does not overflow target_long, regardless of low bits count, right?
Phil.
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