[LLVMdev] reg2mem pass

[Seung Jae Lee]

Hello, guys.
I just tested -reg2mem pass to see how it changes my bitcode.
E.g., for the following simple C code:
-------------------------------------------------------------
int foo() {

  int i,j;
  int sum = 0;
  for (i=0; i<10; i++)
  {
    sum +=  i;
    for (j=0; j<3; j++)
      sum += 2;
  }
  return sum;
}
-------------------------------------------------------------
I could get the corresponding LLVM assembly with llvm-gcc and llvm-dis:
-------------------------------------------------------------
int %foo() {
entry:
	br label %bb8.outer

bb8.outer:		; preds = %bb10, %entry
	%indvar26 = phi uint [ 0, %entry ], [ %indvar.next27, %bb10 ]		; <uint> [#uses=2]
	%sum.0.pn.ph = phi int [ 0, %entry ], [ %sum.1, %bb10 ]		; <int> [#uses=1]
	%i.0.0.ph = cast uint %indvar26 to int		; <int> [#uses=1]
	br label %bb8

bb3:		; preds = %bb8
	%indvar.next = add uint %indvar, 1		; <uint> [#uses=1]
	br label %bb8

bb8:		; preds = %bb3, %bb8.outer
	%indvar = phi uint [ 0, %bb8.outer ], [ %indvar.next, %bb3 ]		; <uint> [#uses=2]
	%sum.0.pn = phi int [ %sum.1, %bb3 ], [ %sum.0.pn.ph, %bb8.outer ]		; <int> [#uses=1]
	%i.0.pn = phi int [ 2, %bb3 ], [ %i.0.0.ph, %bb8.outer ]		; <int> [#uses=1]
	%sum.1 = add int %i.0.pn, %sum.0.pn		; <int> [#uses=3]
	%exitcond = seteq uint %indvar, 3		; <bool> [#uses=1]
	br bool %exitcond, label %bb10, label %bb3

bb10:		; preds = %bb8
	%indvar.next27 = add uint %indvar26, 1		; <uint> [#uses=2]
	%exitcond28 = seteq uint %indvar.next27, 10		; <bool> [#uses=1]
	br bool %exitcond28, label %bb16, label %bb8.outer

bb16:		; preds = %bb10
	ret int %sum.1
}
-------------------------------------------------------------
And I did "opt -reg2mem" for the bitcode, which is emitted like this:
-------------------------------------------------------------
int %foo() {
allocablock:
	%indvar26 = alloca uint		; <uint*> [#uses=3]
	%sum.0.pn.ph = alloca int		; <int*> [#uses=2]
	%i.0.0.ph = alloca int		; <int*> [#uses=2]
	%indvar.next = alloca uint		; <uint*> [#uses=2]
	%indvar = alloca uint		; <uint*> [#uses=3]
	%sum.1 = alloca int		; <int*> [#uses=4]
	%indvar.next27 = alloca uint		; <uint*> [#uses=3]
	br label %entry

entry:		; preds = %allocablock
	br label %bb8.outer

bb8.outer:		; preds = %bb10.bb8.outer_crit_edge, %entry
	%indvar26 = phi uint [ 0, %entry ], [ %indvar.next27.reload, %bb10.bb8.outer_crit_edge ]		; <uint> [#uses=1]
	%sum.0.pn.ph = phi int [ 0, %entry ], [ %sum.1.reload, %bb10.bb8.outer_crit_edge ]		; <int> [#uses=1]
	store uint %indvar26, uint* %indvar26
	store int %sum.0.pn.ph, int* %sum.0.pn.ph
	%indvar26.reload5 = load uint* %indvar26		; <uint> [#uses=1]
	%i.0.0.ph = cast uint %indvar26.reload5 to int		; <int> [#uses=1]
	store int %i.0.0.ph, int* %i.0.0.ph
	%i.0.0.ph.reload = load int* %i.0.0.ph		; <int> [#uses=1]
	%sum.0.pn.ph.reload = load int* %sum.0.pn.ph		; <int> [#uses=1]
	br label %bb8

bb3:		; preds = %bb8
	%indvar.reload = load uint* %indvar		; <uint> [#uses=1]
	%indvar.next = add uint %indvar.reload, 1		; <uint> [#uses=1]
	store uint %indvar.next, uint* %indvar.next
	%sum.1.reload2 = load int* %sum.1		; <int> [#uses=1]
	%indvar.next.reload = load uint* %indvar.next		; <uint> [#uses=1]
	br label %bb8

bb8:		; preds = %bb3, %bb8.outer
	%indvar = phi uint [ 0, %bb8.outer ], [ %indvar.next.reload, %bb3 ]		; <uint> [#uses=1]
	%sum.0.pn = phi int [ %sum.1.reload2, %bb3 ], [ %sum.0.pn.ph.reload, %bb8.outer ]		; <int> [#uses=1]
	%i.0.pn = phi int [ 2, %bb3 ], [ %i.0.0.ph.reload, %bb8.outer ]		; <int> [#uses=1]
	store uint %indvar, uint* %indvar
	%sum.1 = add int %i.0.pn, %sum.0.pn		; <int> [#uses=1]
	store int %sum.1, int* %sum.1
	%indvar.reload4 = load uint* %indvar		; <uint> [#uses=1]
	%exitcond = seteq uint %indvar.reload4, 3		; <bool> [#uses=1]
	br bool %exitcond, label %bb10, label %bb3

bb10:		; preds = %bb8
	%indvar26.reload = load uint* %indvar26		; <uint> [#uses=1]
	%indvar.next27 = add uint %indvar26.reload, 1		; <uint> [#uses=1]
	store uint %indvar.next27, uint* %indvar.next27
	%indvar.next27.reload1 = load uint* %indvar.next27		; <uint> [#uses=1]
	%exitcond28 = seteq uint %indvar.next27.reload1, 10		; <bool> [#uses=1]
	br bool %exitcond28, label %bb16, label %bb10.bb8.outer_crit_edge

bb10.bb8.outer_crit_edge:		; preds = %bb10
	%indvar.next27.reload = load uint* %indvar.next27		; <uint> [#uses=1]
	%sum.1.reload = load int* %sum.1		; <int> [#uses=1]
	br label %bb8.outer

bb16:		; preds = %bb10
	%sum.1.reload3 = load int* %sum.1		; <int> [#uses=1]
	ret int %sum.1.reload3
}
-------------------------------------------------------------
Sorry for this long code.
After -reg2mem, I could find any of PHIs weren't eliminated.
I just wonder if this is normal.

Thanks,
Seung J. Lee