Eliminate vectorizer analysis side effects

[Xinliang David Li <davidxl at google dot com>]

I was debugging a runtime failure of SPEC06 xalancbmk built with LIPO.
Using -fdisable-<pass> option pinpoints the problem in slp vectorize
pass on a particular function. dbgcnt support is added to to track
down the individual BB, but it  fails even when the dbg count is set
to 0.

It turns out that no BB was actually vectorized for that function, but
turning on/off slp-vectorize does make a difference in generated code
-- the only difference between the good and bad case is stack layout.
 The problem is  in the alignment analysis phase -- which
speculatively changes the base declaration's alignment regardless
whether the vectorization transformation will be performed or not
later.

The attached patch fixes the problem. Testing is ok. Ok for trunk?

thanks,

David

Attachment: vect_analy_fix.txt
Description: Text document