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Remove some stuff that now works

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@25963 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nate Begeman 2006-02-04 07:29:35 +00:00
parent 0d913eaaed
commit a6973c348b
1 changed files with 0 additions and 53 deletions
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53
lib/Target/PowerPC/README.txt
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@ -198,59 +198,6 @@ currently only commutes to avoid inserting a copy BEFORE the two addr instr.
===-------------------------------------------------------------------------===
176.gcc contains a bunch of code like this (this occurs dozens of times):
int %test(uint %mode.0.i.0) {
%tmp.79 = cast uint %mode.0.i.0 to sbyte ; <sbyte> [#uses=1]
%tmp.80 = cast sbyte %tmp.79 to int ; <int> [#uses=1]
%tmp.81 = shl int %tmp.80, ubyte 16 ; <int> [#uses=1]
%tmp.82 = and int %tmp.81, 16711680
ret int %tmp.82
}
which we compile to:
_test:
extsb r2, r3
rlwinm r3, r2, 16, 8, 15
blr
The extsb is obviously dead. This can be handled by a future thing like
MaskedValueIsZero that checks to see if bits are ever demanded (in this case,
the sign bits are never used, so we can fold the sext_inreg to nothing).
I'm seeing code like this:
srwi r3, r3, 16
extsb r3, r3
rlwimi r4, r3, 16, 8, 15
in which the extsb is preventing the srwi from being nuked.
===-------------------------------------------------------------------------===
Another example that occurs is:
uint %test(int %specbits.6.1) {
%tmp.2540 = shr int %specbits.6.1, ubyte 11 ; <int> [#uses=1]
%tmp.2541 = cast int %tmp.2540 to uint ; <uint> [#uses=1]
%tmp.2542 = shl uint %tmp.2541, ubyte 13 ; <uint> [#uses=1]
%tmp.2543 = and uint %tmp.2542, 8192 ; <uint> [#uses=1]
ret uint %tmp.2543
}
which we codegen as:
l1_test:
srawi r2, r3, 11
rlwinm r3, r2, 13, 18, 18
blr
the srawi can be nuked by turning the SAR into a logical SHR (the sext bits are
dead), which I think can then be folded into the rlwinm.
===-------------------------------------------------------------------------===
Compile offsets from allocas:
int *%test() {