SSA: Prefer swapping instead of shrinking followed by dupping

Previously, if a slot is desirable to be dupped, but is out of reach, we
would try to shrink the stack and then bringing it to reachable region.
However, even if it is out-of-reach for dup, it might still be in reach
for swap, so if it is safe to swap, we can do it directly.

Author: blishko

libyul/backends/evm/ssa/StackShuffler.h

@@ -347,6 +347,12 @@ class StackShuffler
 			}
 			else
 			{
+				// even if it is not dup reachable, it still might be swappable
+				if (_stack.swapReachable(sourceOffset) && _state.isSafeToSwapWithTop(sourceOffset))
+				{
+					_stack.swap(sourceOffset);
+					return true;
+				}
 				// the slot we need something in the args region of is unreachable, try compressing the stack,
 				// first looking at the top
 				if (shrinkStack(_stack, _state))

test/libyul/ssa/stackShuffler/deep_argument_shrink.stack

@@ -9,12 +9,8 @@ targetStackSize: 19
 //    (initial)|    v12      *      *      *      *      *      *      *      *      *      *      *      *    v68      * phi111    v84 |    v86
 //        SWAP3|    v12      *      *      *      *      *      *      *      *      *      *      *      *    v68    v86 phi111    v84 |      *
 //          POP|    v12      *      *      *      *      *      *      *      *      *      *      *      *    v68    v86 phi111    v84
-//        SWAP2|    v12      *      *      *      *      *      *      *      *      *      *      *      *    v68    v84 phi111    v86
-//        SWAP4|    v12      *      *      *      *      *      *      *      *      *      *      *    v86    v68    v84 phi111      *
-//          POP|    v12      *      *      *      *      *      *      *      *      *      *      *    v86    v68    v84 phi111
-//       SWAP15| phi111      *      *      *      *      *      *      *      *      *      *      *    v86    v68    v84    v12
-//         DUP4| phi111      *      *      *      *      *      *      *      *      *      *      *    v86    v68    v84    v12    v86
-//         DUP2| phi111      *      *      *      *      *      *      *      *      *      *      *    v86    v68    v84    v12    v86 |    v12
-//         DUP2| phi111      *      *      *      *      *      *      *      *      *      *      *    v86    v68    v84    v12    v86 |    v12    v86
+//       SWAP16|    v84      *      *      *      *      *      *      *      *      *      *      *      *    v68    v86 phi111    v12
+//         DUP1|    v84      *      *      *      *      *      *      *      *      *      *      *      *    v68    v86 phi111    v12 |    v12
+//         DUP4|    v84      *      *      *      *      *      *      *      *      *      *      *      *    v68    v86 phi111    v12 |    v12    v86
 //             +----------------------------------------------------------------------------------------------------------------------- +--------------
 //     (target)|                                                                                                     {v68, v84, phi111} |    v12    v86