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a bad case for bitfield insert

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@24051 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2005-10-28 00:20:45 +00:00
parent 0d841e0567
commit 0195910558
1 changed files with 34 additions and 0 deletions
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34
lib/Target/PowerPC/README.txt
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@ -185,3 +185,37 @@ doesn't get folded into the rlwimi instruction. We should ideally see through
things like this, rather than forcing llvm to generate the equivalent things like this, rather than forcing llvm to generate the equivalent
(shl (add bitfield, C2), C1) with some kind of mask. (shl (add bitfield, C2), C1) with some kind of mask.
===-------------------------------------------------------------------------===
Compile this (standard bitfield insert of a constant):
void %test(uint* %tmp1) {
%tmp2 = load uint* %tmp1 ; <uint> [#uses=1]
%tmp5 = or uint %tmp2, 257949696 ; <uint> [#uses=1]
%tmp6 = and uint %tmp5, 4018143231 ; <uint> [#uses=1]
store uint %tmp6, uint* %tmp1
ret void
}
to:
_test:
lwz r0,0(r3)
li r2,123
rlwimi r0,r2,21,3,10
stw r0,0(r3)
blr
instead of:
_test:
lis r2, -4225
lwz r4, 0(r3)
ori r2, r2, 65535
oris r4, r4, 3936
and r2, r4, r2
stw r2, 0(r3)
blr