[llvm-commits] [llvm] r122654 - in /llvm/trunk: lib/Analysis/InstructionSimplify.cpp lib/Target/README.txt test/Transforms/InstSimplify/2010-12-31-ValueNumber.ll

[Chris Lattner]

On Jan 1, 2011, at 12:11 PM, Duncan Sands wrote:

> Hi Chris,
> 
>>> Fix a README item by having InstructionSimplify do a mild form of value
>>> numbering, in which it considers (for example) "%a = add i32 %x, %y" and
>>> "%b = add i32 %x, %y" to be equal because the operands are equal and the
>>> result of the instructions only depends on the values of the operands.
>>> This has almost no effect (it removes 4 instructions from gcc-as-one-file),
>>> and perhaps slows down compilation: I measured a 0.4% slowdown on the large
>>> gcc-as-one-file testcase, but it wasn't statistically significant.
>> 
>> Duncan, please don't do this. InstSimplify should *not* do CSE, which is what the README entry is about.  I should not have added the readme entry as I did, because the actual issue is lack of early CSE.  I have another way to fix this, which I'll be tackling shortly.
> 
> no problem, reverted in commit 122661.

Thanks Duncan!!

-Chris