[llvm] [SimplifyCFG] Delete the unnecessary range check for small mask operation (PR #65835)

[via llvm-commits]

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@@ -0,0 +1,57 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -passes=simplifycfg --switch-to-lookup -S < %s | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+; https://alive2.llvm.org/ce/z/tuxLhJ
+define i1 @switch_lookup_with_small_mask(i64 %x) {
+; CHECK-LABEL: @switch_lookup_with_small_mask(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[AND:%.*]] = and i64 [[X:%.*]], 15
+; CHECK-NEXT:    [[SWITCH_CAST:%.*]] = trunc i64 [[AND]] to i16
+; CHECK-NEXT:    [[SWITCH_SHIFTAMT:%.*]] = mul nuw nsw i16 [[SWITCH_CAST]], 1
+; CHECK-NEXT:    [[SWITCH_DOWNSHIFT:%.*]] = lshr i16 1030, [[SWITCH_SHIFTAMT]]
+; CHECK-NEXT:    [[SWITCH_MASKED:%.*]] = trunc i16 [[SWITCH_DOWNSHIFT]] to i1
+; CHECK-NEXT:    ret i1 [[SWITCH_MASKED]]
+;
+entry:
+  %and = and i64 %x, 15
+  switch i64 %and, label %default [
+  i64 10, label %lor.end
+  i64 1, label %lor.end
+  i64 2, label %lor.end
+  ]
+
+default:                                          ; preds = %entry
+  br label %lor.end
+
+lor.end:                                          ; preds = %entry, %entry, %entry, %default
+  %0 = phi i1 [ true, %entry ], [ false, %default ], [ true, %entry ], [ true, %entry ]
+  ret i1 %0
+}
+
+define i1 @switch_lookup_with_small_urem(i64 %x) {
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zmodem wrote:

This isn't much different from the previous test case. Maybe we could skip it?

https://github.com/llvm/llvm-project/pull/65835