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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/68837] PowerPC switch statement performance
Date: Thu, 11 Jun 2020 05:15:06 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D68837

--- Comment #5 from HaoChen Gui <guihaoc at gcc dot gnu.org> ---
I think there are two ways avoiding sign extension for offset loading.

a. Make sure all offsets be positive.  There exists backward jumps as well =
as
STC will reorder the basic block. So the offset might be negative. We can c=
heck
the offsets after bb-reorder pass and remove sign extension if all offsets =
are
positive. It may need a new pass.

b. Use absolute addresses instead of offsets. It's controlled by macro
CASE_VECTOR_PC_RELATIVE and flag_pic. x86 uses absolute address(labels) in
their jump table, though the size of jump is bigger. Power haven't supported
absolute address yet.=