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[InstCombine] fold bitcasts around an extractelement (3rd try)

Description

[InstCombine] fold bitcasts around an extractelement (3rd try)

This is a redo of r255137 (reverted at r255227) which was a redo of
r255124 (reverted at r255126) with a fixed check for a scalar source
type and an added test for the failure that caused the revert.

Original commit message:

Example:

bitcast (extractelement (bitcast <2 x float> %X to <2 x i32>), 1) to float
  --->
extractelement <2 x float> %X, i32 1

This is part of fixing PR25543:
https://llvm.org/bugs/show_bug.cgi?id=25543

The next step will be to generalize this fold:
trunc ( lshr ( bitcast X) ) -> extractelement (X)

Ie, I'm hoping to replace the existing transform of:
bitcast ( trunc ( lshr ( bitcast X)))
added by:
http://reviews.llvm.org/rL112232

with 2 less specific transforms to catch the case in the bug report.

Differential Revision: http://reviews.llvm.org/D14879

Details

Committed
spatelDec 10 2015, 9:09 AM
Differential Revision
D14879: [InstCombine] fold bitcasts around an extractelement
Parents
rL255260: Add modules downloaded by ModuleCache to the global ModuleList
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