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

[Min-Yih Hsu via llvm-commits]

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@@ -105,3 +105,55 @@ 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) {
+; RV32-LABEL: test_fshl_i32:
+; RV32:       # %bb.0:
+; RV32-NEXT:    not a3, a2
+; RV32-NEXT:    sll a0, a0, a2
+; RV32-NEXT:    srli a1, a1, 1
+; RV32-NEXT:    srl a1, a1, a3
+; RV32-NEXT:    or a0, a0, a1
+; RV32-NEXT:    ret
+;
+; RV64-LABEL: test_fshl_i32:
+; RV64:       # %bb.0:
+; RV64-NEXT:    not a3, a2
+; RV64-NEXT:    sllw a0, a0, a2
+; RV64-NEXT:    srliw a1, a1, 1
+; RV64-NEXT:    srlw a1, a1, a3
+; RV64-NEXT:    or a0, a0, a1
+; RV64-NEXT:    ret
+  %fshl = call i32 @llvm.fshl.i32(i32 %x, i32 %_, i32 %y)
+  %shl = shl i32 %x, %y
+  %or = or i32 %fshl, %shl
+  %and = and i32 %or, %fshl
+  %trunc = trunc i32 %and to i16
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mshockwave wrote:

> If these are for testing multi-use cases as mentioned in the sibling comment: (1) usually we have a normal test case that checks whether the transformation fires. In addition, we have another negative test case to make sure the transformation doesn't fire with undesired conditions. So you need two kinds of test cases, while I believe you only have one here.
(2) Maybe I miss something, but where did you check whether the funnel shift and the shift have one use?

What about these two things? Namely the negative test case and the one-use check.

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