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

[Duncan Sands]

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.

Ciao, Duncan.