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From: "guihaoc at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/95737] PPC: Unnecessary extsw after negative less than
Date: Fri, 14 Jan 2022 09:16:14 +0000	[thread overview]
Message-ID: <bug-95737-4-C7WbmgOjTV@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-95737-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95737

--- Comment #9 from HaoChen Gui <guihaoc at gcc dot gnu.org> ---
Add a pattern to convert the plus mode to DI. 

+(define_insn_and_split "*my_split"
+  [(set (match_operand:DI 0 "gpc_reg_operand")
+       (sign_extend:DI (plus:SI (match_operand:SI 1 "ca_operand")
+                                (const_int -1))))]
+  ""
+  "#"
+  ""
+  [(parallel [(set (match_dup 0)
+                  (plus:DI (match_dup 2)
+                           (const_int -1)))
+             (clobber (match_dup 2))])]
+{
+  operands[2] = copy_rtx (operands[1]);
+  PUT_MODE (operands[2], DImode);
+})

With the patch, the "extsw" could be optimized out. I compared the performance
between P8 code (with the patch) and P9 code. The performance of P9 is better. 
ISA says that computation with CA causes additional latency. It should be true.
The only concern is P9 code uses more register.

  parent reply	other threads:[~2022-01-14  9:16 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-18  8:10 [Bug target/95737] New: " jens.seifert at de dot ibm.com
2020-06-19 16:40 ` [Bug target/95737] " wschmidt at gcc dot gnu.org
2020-06-19 16:42 ` wschmidt at gcc dot gnu.org
2020-06-19 17:43 ` jens.seifert at de dot ibm.com
2020-06-21 15:35 ` wschmidt at linux dot ibm.com
2020-06-21 16:30 ` segher at gcc dot gnu.org
2022-01-06  5:39 ` guihaoc at gcc dot gnu.org
2022-01-13 12:19 ` segher at gcc dot gnu.org
2022-01-13 16:34 ` segher at gcc dot gnu.org
2022-01-14  9:16 ` guihaoc at gcc dot gnu.org [this message]
2022-05-18  5:24 ` cvs-commit at gcc dot gnu.org
2022-07-29  2:52 ` guihaoc at gcc dot gnu.org

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