optimization/3978: arm peephole for loading two consecutive memory locations generates suboptimal code (on arm7tdmi)

[Philip Blundell]

The following reply was made to PR optimization/3978; it has been noted by GNATS.

From: Philip Blundell <philb@gnu.org>
To: segher@chello.nl
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: optimization/3978: arm peephole for loading two consecutive memory locations generates suboptimal code (on arm7tdmi) 
Date: Thu, 09 Aug 2001 22:12:51 +0100

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 >I often see generated code like
 >
 >add   temp, pointer, #offset
 >ldmia temp, {regA, regB}
 >
 >(after which temp is dead)
 >
 >which is slower than just
 >
 >ldr regA, [pointer, #offset]
 >ldr regB, [pointer, #offset+4]
 >
 >and wastes a register as well
 
 Use -mtune=arm8 or some such.  I don't think this will do any harm on 
 ARM7TDMI and it should yield the results you are looking for.
 
 p.
 
 
 
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