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

[via llvm-commits]

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@@ -0,0 +1,112 @@
+; 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_i1(i64 %x) {
+; CHECK-LABEL: @switch_lookup_with_small_i1(
+; 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
+}
+
+; https://godbolt.org/z/sjbjorKon
+define i8 @switch_lookup_with_small_i8(i64 %x) {
+; CHECK-LABEL: @switch_lookup_with_small_i8(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[REM:%.*]] = urem i64 [[X:%.*]], 5
+; CHECK-NEXT:    [[SWITCH_CAST:%.*]] = trunc i64 [[REM]] to i40
+; CHECK-NEXT:    [[SWITCH_SHIFTAMT:%.*]] = mul nuw nsw i40 [[SWITCH_CAST]], 8
+; CHECK-NEXT:    [[SWITCH_DOWNSHIFT:%.*]] = lshr i40 460303, [[SWITCH_SHIFTAMT]]
+; CHECK-NEXT:    [[SWITCH_MASKED:%.*]] = trunc i40 [[SWITCH_DOWNSHIFT]] to i8
+; CHECK-NEXT:    ret i8 [[SWITCH_MASKED]]
+;
+entry:
+  %rem = urem i64 %x, 5
+  switch i64 %rem, label %default [
+  i64 0, label %sw.bb0
+  i64 1, label %sw.bb1
+  i64 2, label %sw.bb2
+  ]
+
+sw.bb0:                                           ; preds = %entry
+  br label %lor.end
+
+sw.bb1:                                           ; preds = %entry
+  br label %lor.end
+
+sw.bb2:                                           ; preds = %entry
+  br label %lor.end
+
+default:                                          ; preds = %entry
+  br label %lor.end
+
+lor.end:
+  %0 = phi i8 [ 15, %sw.bb0 ], [ 6, %sw.bb1 ], [ 7, %sw.bb2 ], [ 0, %default ]
+  ret i8 %0
+}
+
+; Negative test: Table size would not fit the register.
+define i32 @switch_lookup_with_small_i32_negative(i64 %x) {
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vfdff wrote:

update, now it has a branch with loopup table

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