[llvm] [SelectionDAG] Add MaskedValueIsZero check to allow folding of zero extended variables we know are safe to extend (PR #85573)

[Simon Pilgrim via llvm-commits]

================
@@ -322,5 +322,144 @@ define void @g(i32 %a) nounwind {
   ret void
 }
 
+define i32 @shift_zext_shl(i8 zeroext %x) {
+; X86-LABEL: shift_zext_shl:
+; X86:       # %bb.0:
+; X86-NEXT:    movzbl {{[0-9]+}}(%esp), %eax
+; X86-NEXT:    andl $64, %eax
+; X86-NEXT:    shll $9, %eax
+; X86-NEXT:    retl
+;
+; X64-LABEL: shift_zext_shl:
+; X64:       # %bb.0:
+; X64-NEXT:    movl %edi, %eax
+; X64-NEXT:    andl $64, %eax
+; X64-NEXT:    shll $9, %eax
+; X64-NEXT:    retq
+  %a = and i8 %x, 64
+  %b = zext i8 %a to i16
+  %c = shl i16 %b, 9
+  %d = zext i16 %c to i32
+  ret i32 %d
+}
+
+define i32 @shift_zext_shl2(i8 zeroext %x) {
+; X86-LABEL: shift_zext_shl2:
+; X86:       # %bb.0:
+; X86-NEXT:    movzbl {{[0-9]+}}(%esp), %eax
+; X86-NEXT:    andl $64, %eax
+; X86-NEXT:    shll $9, %eax
+; X86-NEXT:    retl
+;
+; X64-LABEL: shift_zext_shl2:
+; X64:       # %bb.0:
+; X64-NEXT:    movl %edi, %eax
+; X64-NEXT:    andl $64, %eax
+; X64-NEXT:    shll $9, %eax
+; X64-NEXT:    retq
+  %a = and i8 %x, 64
+  %b = zext i8 %a to i32
+  %c = shl i32 %b, 9
+  ret i32 %c
+}
+
+define <4 x i32> @shift_zext_shl_vec(<4 x i8> %x) {
----------------
RKSimon wrote:

Add nounwind to get rid of CFI noise

https://github.com/llvm/llvm-project/pull/85573