[PATCH] D16829: An implementation of Swing Modulo Scheduling

[Mingjie Xing via llvm-commits]

xmj added a subscriber: xmj.
xmj added a comment.

I'm just wondering how to generate a loop which has only one basic block.  For an example,

extern int a, b[10];

void foo(void)
{

  for (int i = 0; i < 10; ++i) {
    a += b[i];
  }

}

Run clang -emit-llvm -S --target=hexagon foo.c will generate

for.cond:                                         ; preds = %for.inc, %entry

  %0 = load i32, i32* %i, align 4
  %cmp = icmp slt i32 %0, 10
  br i1 %cmp, label %for.body, label %for.end

for.body:                                         ; preds = %for.cond

  %1 = load i32, i32* %i, align 4
  %arrayidx = getelementptr inbounds [10 x i32], [10 x i32]* @b, i32 0, i32 %1
  %2 = load i32, i32* %arrayidx, align 4
  %3 = load i32, i32* @a, align 4
  %add = add nsw i32 %3, %2
  store i32 %add, i32* @a, align 4
  br label %for.inc

...

Thus the swp will not be done due to the constraint.

(gdb) p L->getNumBlocks()
$2 = 2


http://reviews.llvm.org/D16829