[llvm-commits] [llvm] r122704 - in /llvm/trunk: lib/Transforms/Scalar/LoopIdiomRecognize.cpp test/Transforms/LoopIdiom/basic.ll

[Duncan Sands]

Hi Chris,

> enhance loop idiom recognition to scan *all* unconditionally executed
> blocks in a loop, instead of just the header block.  This makes it more
> aggressive, able to handle Duncan's Ada examples.

thanks for doing this!  I noticed two issues with the examples I sent you,
which now compile to

define void @ubytezero([256 x i32]* %a) nounwind {
return:
   %tmp32 = getelementptr [256 x i32]* %a, i32 0, i32 0
   store i32 0, i32* %tmp32, align 4
   %scevgep = getelementptr [256 x i32]* %a, i32 0, i32 1
   %scevgep4 = bitcast i32* %scevgep to i8*
   call void @llvm.memset.p0i8.i32(i8* %scevgep4, i8 0, i32 1020, i32 4, i1 false)
   ret void
}

define void @uintzero(i32* %a) nounwind {
return:
   store i32 0, i32* %a, align 4
   %scevgep = getelementptr i32* %a, i32 1
   %scevgep3 = bitcast i32* %scevgep to i8*
   call void @llvm.memset.p0i8.i32(i8* %scevgep3, i8 0, i32 -4, i32 4, i1 false)
   ret void
}

In both functions the memset could also take care of the store to the first
element, rather than starting from the second element.  However maybe merging
the store and the memset should be a job for a different pass.

Secondly, notice that the size of the memset in the second function is -4.
Hopefully this will work correctly (i.e. memset 2^32-4 values)!  It did make
me wonder what happens if the loop stores say 2^32 or 2^48 values.  Presumably
the type of the memset size argument is automagically set to a size that can
hold the loop trip count...

Ciao, Duncan.