[llvm] [InstCombine] Generalize trunc-shift-icmp fold from (1 << Y) to (Pow2 << Y) (PR #169163)

[Pedro Lobo via llvm-commits]

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@@ -526,24 +520,36 @@ define i1 @shl2_trunc_eq8_i32(i32 %a) {
 }
 
 define i1 @shl2_trunc_ne8_i32(i32 %a) {
-; DL64-LABEL: @shl2_trunc_ne8_i32(
-; DL64-NEXT:    [[SHL:%.*]] = shl i32 2, [[A:%.*]]
-; DL64-NEXT:    [[TMP1:%.*]] = and i32 [[SHL]], 65534
-; DL64-NEXT:    [[R:%.*]] = icmp ne i32 [[TMP1]], 8
-; DL64-NEXT:    ret i1 [[R]]
-;
-; DL8-LABEL: @shl2_trunc_ne8_i32(
-; DL8-NEXT:    [[SHL:%.*]] = shl i32 2, [[A:%.*]]
-; DL8-NEXT:    [[T:%.*]] = trunc i32 [[SHL]] to i16
-; DL8-NEXT:    [[R:%.*]] = icmp ne i16 [[T]], 8
-; DL8-NEXT:    ret i1 [[R]]
+; CHECK-LABEL: @shl2_trunc_ne8_i32(
+; CHECK-NEXT:    [[R:%.*]] = icmp ne i32 [[A:%.*]], 2
+; CHECK-NEXT:    ret i1 [[R]]
 ;
   %shl = shl i32 2, %a
   %t = trunc i32 %shl to i16
   %r = icmp ne i16 %t, 8
   ret i1 %r
 }
 
+define i1 @neg_shl2_trunc_eq0_i8(i8 %a) {
+; CHECK-LABEL: @neg_shl2_trunc_eq0_i8(
+; CHECK-NEXT:    ret i1 true
+;
+  %shl = shl i8 256, %a
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pedroclobo wrote:

Right, thanks!

https://github.com/llvm/llvm-project/pull/169163