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<div style="direction: ltr;font-family: Tahoma;color: #000000;font-size: 10pt;">Hi,<br>
<br>
A bit more information.<br>
I believe my problem lies with the fact that the load is left as 'anyext from i8'.<br>
On the XCore target we know this will become an 8bit zext load - as there is no 8bit sign extended load!<br>
If BB#1 were to force the load to a "zext from i8" would this information be available in BB#2?<br>
<br>
BB#1:<br>
0x268c1b0: i32 = Register %vreg1 [ID=3]<br>
0x2689d80: i32,ch = load 0x265d380, 0x2689f80, 0x268b9b0<LD1[%s2], anyext from i8> [ORD=4] [ID=5]<br>
0x2689e80: ch = CopyToReg 0x265d380, 0x268c1b0, 0x2689d80 [ORD=4] [ID=6]<br>
<br>
BB#2:<br>
0x268a480: i32 = Register %vreg1 [ID=1]<br>
0x268bbb0: i32,ch = CopyFromReg 0x265d380, 0x268a480 [ORD=6] [ID=7]<br>
0x268a080: i32 = Constant<255> [ID=6]<br>
0x268bdb0: i32 = and 0x268bbb0, 0x268a080 [ORD=6] [ID=8]<br>
0x2689e80: i32 = Constant<0> [ID=5]<br>
0x268c1b0: ch = seteq [ID=2]<br>
0x268a880: i32 = setcc 0x268bdb0, 0x2689e80, 0x268c1b0 [ORD=6] [ID=9]<br>
<br>
Robert<br>
<br>
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<div style="direction: ltr;" id="divRpF771975"><font color="#000000" face="Tahoma" size="2"><b>From:</b> llvmdev-bounces@cs.uiuc.edu [llvmdev-bounces@cs.uiuc.edu] on behalf of Robert Lytton [robert@xmos.com]<br>
<b>Sent:</b> 06 September 2013 17:18<br>
<b>To:</b> llvmdev@cs.uiuc.edu<br>
<b>Subject:</b> [LLVMdev] removing unnecessary ZEXT<br>
</font><br>
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<div style="direction:ltr; font-family:Tahoma; color:#000000; font-size:10pt">Hi,<br>
<br>
Within a basic block I can remove unnecessary register copies + zero sign extensions of unsigned-8bit-loaded values by implementing isZExtFree() for ISD::LOAD nodes.<br>
...But not between basic blocks.<br>
<br>
The first block does a CopyFromReg of the unsigned-8bit-loaded vreg1 into a new vreg2.<br>
The second block then does a unnecessary zext to vreg2.<br>
What I want is the 2nd block to use the original vreg1!<br>
What I am getting is one extra register clobber and two extra instructions.<br>
<br>
I have looked at other targets to see what they do but can't see what I am missing.<br>
<br>
Help please!<br>
Thank you<br>
<br>
Robert<br>
<br>
<br>
<br>
<br>
<br>
<br>
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