[llvm] [DAG] Add generic i8 CTPOP lowering using i32 MUL (PR #79989)

[Phoebe Wang via llvm-commits]

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@@ -59,16 +46,13 @@ define i8 @cnt8(i8 %x) nounwind readnone {
 ;
 ; X64-NDD-LABEL: cnt8:
 ; X64-NDD:       # %bb.0:
-; X64-NDD-NEXT:    shrb %dil, %al
-; X64-NDD-NEXT:    andb $85, %al
-; X64-NDD-NEXT:    subb %al, %dil, %al
-; X64-NDD-NEXT:    andb $51, %al, %cl
-; X64-NDD-NEXT:    shrb $2, %al
-; X64-NDD-NEXT:    andb $51, %al
-; X64-NDD-NEXT:    addb %cl, %al
-; X64-NDD-NEXT:    shrb $4, %al, %cl
-; X64-NDD-NEXT:    addb %cl, %al
-; X64-NDD-NEXT:    andb $15, %al
+; X64-NDD-NEXT:    movzbl %dil, %eax
+; X64-NDD-NEXT:    imull $134480385, %eax, %eax # imm = 0x8040201
+; X64-NDD-NEXT:    shrl $3, %eax
+; X64-NDD-NEXT:    andl $286331153, %eax # imm = 0x11111111
+; X64-NDD-NEXT:    imull $286331153, %eax, %eax # imm = 0x11111111
+; X64-NDD-NEXT:    shrl $28, %eax
+; X64-NDD-NEXT:    # kill: def $al killed $al killed $eax
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phoebewang wrote:

Any chance to merge the three together?

https://github.com/llvm/llvm-project/pull/79989