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

[Nikita Popov 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) {
----------------
nikic wrote:

This test fails switch to lookup table conversion entirely. What we want is that it creates the lookup table with the branch, but wouldn't create it is we increased the range.

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