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Re: 0003-Improve-VBEout-computation.patch
- From: Paolo Bonzini <bonzini at gnu dot org>
- To: Maxim Kuvyrkov <maxim at codesourcery dot com>
- Cc: Jeff Law <law at redhat dot com>, gcc-patches <gcc-patches at gcc dot gnu dot org>
- Date: Wed, 16 Jun 2010 18:57:59 +0200
- Subject: Re: 0003-Improve-VBEout-computation.patch
- References: <4C18F225.2040509@codesourcery.com> <4C18F446.20508@codesourcery.com>
+ that are calculated along every path from BB.
+ E.g., it will not try to optimize the following case:
+
+ 2
+ | \
+ 3* |
+ | /
+ 4
+ / \
+ 5* 6
+
+ ;; "*" marks basic blocks that calculate same expression
+ ;; Ideally, all calculation would be moved to block 2.
No, this pessimizes the path 2->4->6. It may cause a massive number of
expressions to be hoisted above switch statements, see PR24123 for a
similar failure.
Paolo