[llvm] [GISel] funnel shift combiner port from SelectionDAG ISel to GlobalISel (PR #135132)

[Min-Yih Hsu via llvm-commits]

================
@@ -105,3 +105,53 @@ define i16 @test_shl_i48_2(i48 %x, i48 %y) {
   %trunc = trunc i48 %shl to i16
   ret i16 %trunc
 }
+
+define i16 @test_fshl_i32(i32 %x, i32 %_, i32 %y) {
----------------
mshockwave wrote:

could you create two commits for this PR: the first one contains only the new test functions you added (e.g. test_fshl_i32 here) but with CHECK lines showing the unoptimized assembly code. And the second commit being your changes, in which the CHECK lines are updated with optimized code.
With such, it's easier to see the changes made by your patch by comparing the differences of the CHECK lines between the two commits. The first commit is also known as "pre-commit test"

https://github.com/llvm/llvm-project/pull/135132