[llvm] [X86] Select i8 ANDN via i32 promotion (PR #205050)

[via llvm-commits]

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@@ -165,25 +165,45 @@ define i16 @andnot_rotl_i16(i16 %a0, i16 %a1, i16 %a2) nounwind {
 }
 
 define i8 @andnot_rotl_i8(i8 %a0, i8 %a1, i8 %a2) nounwind {
-; X86-LABEL: andnot_rotl_i8:
-; X86:       # %bb.0:
-; X86-NEXT:    movzbl {{[0-9]+}}(%esp), %ecx
-; X86-NEXT:    movzbl {{[0-9]+}}(%esp), %eax
-; X86-NEXT:    rolb %cl, %al
-; X86-NEXT:    notb %al
-; X86-NEXT:    andb {{[0-9]+}}(%esp), %al
-; X86-NEXT:    retl
+; X86-NOBMI-LABEL: andnot_rotl_i8:
+; X86-NOBMI:       # %bb.0:
+; X86-NOBMI-NEXT:    movzbl {{[0-9]+}}(%esp), %ecx
+; X86-NOBMI-NEXT:    movzbl {{[0-9]+}}(%esp), %eax
+; X86-NOBMI-NEXT:    rolb %cl, %al
+; X86-NOBMI-NEXT:    notb %al
+; X86-NOBMI-NEXT:    andb {{[0-9]+}}(%esp), %al
+; X86-NOBMI-NEXT:    retl
 ;
-; X64-LABEL: andnot_rotl_i8:
-; X64:       # %bb.0:
-; X64-NEXT:    movl %edx, %ecx
-; X64-NEXT:    movl %esi, %eax
-; X64-NEXT:    # kill: def $cl killed $cl killed $ecx
-; X64-NEXT:    rolb %cl, %al
-; X64-NEXT:    notb %al
-; X64-NEXT:    andb %dil, %al
-; X64-NEXT:    # kill: def $al killed $al killed $eax
-; X64-NEXT:    retq
+; X86-BMI-LABEL: andnot_rotl_i8:
+; X86-BMI:       # %bb.0:
+; X86-BMI-NEXT:    movzbl {{[0-9]+}}(%esp), %ecx
+; X86-BMI-NEXT:    movzbl {{[0-9]+}}(%esp), %eax
+; X86-BMI-NEXT:    rolb %cl, %al
+; X86-BMI-NEXT:    movzbl %al, %eax
+; X86-BMI-NEXT:    andnl {{[0-9]+}}(%esp), %eax, %eax
+; X86-BMI-NEXT:    # kill: def $al killed $al killed $eax
+; X86-BMI-NEXT:    retl
+;
+; X64-NOBMI-LABEL: andnot_rotl_i8:
+; X64-NOBMI:       # %bb.0:
+; X64-NOBMI-NEXT:    movl %edx, %ecx
+; X64-NOBMI-NEXT:    movl %esi, %eax
+; X64-NOBMI-NEXT:    # kill: def $cl killed $cl killed $ecx
+; X64-NOBMI-NEXT:    rolb %cl, %al
+; X64-NOBMI-NEXT:    notb %al
+; X64-NOBMI-NEXT:    andb %dil, %al
+; X64-NOBMI-NEXT:    # kill: def $al killed $al killed $eax
+; X64-NOBMI-NEXT:    retq
+;
+; X64-BMI-LABEL: andnot_rotl_i8:
+; X64-BMI:       # %bb.0:
+; X64-BMI-NEXT:    movl %edx, %ecx
+; X64-BMI-NEXT:    # kill: def $cl killed $cl killed $ecx
+; X64-BMI-NEXT:    rolb %cl, %sil
+; X64-BMI-NEXT:    movzbl %sil, %eax
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mygitljf wrote:

Yes, the high bits are undemanded. This `movzbl` is how X86 realizes the GR8 any-extend here and also avoids a partial-register update.

https://github.com/llvm/llvm-project/pull/205050