[llvm] [SDAG] Use shifts if ISD::MUL is illegal when lowering ISD::CTPOP (PR #86505)

[Matt Arsenault via llvm-commits]

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@@ -285,9 +285,12 @@ define i32 @test_ctpop_i32(i32 %a) nounwind {
 ; LA64-NEXT:    lu12i.w $a1, 61680
 ; LA64-NEXT:    ori $a1, $a1, 3855
 ; LA64-NEXT:    and $a0, $a0, $a1
-; LA64-NEXT:    lu12i.w $a1, 4112
-; LA64-NEXT:    ori $a1, $a1, 257
-; LA64-NEXT:    mul.d $a0, $a0, $a1
+; LA64-NEXT:    slli.d $a1, $a0, 8
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arsenm wrote:

LegalizerInfo::getAction is the closest thing, which will show you the next legalization step. We currently are lacking helpers to iteratively walk through chains of legalization to find the ultimate type 

https://github.com/llvm/llvm-project/pull/86505