[llvm] [ConstantRange] Improve ConstantRange::binaryXor (PR #80146)

[via llvm-commits]

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@@ -0,0 +1,55 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt < %s -passes=ipsccp -S | FileCheck %s
+
+; Tests from PR79696
+
+define i1 @constant_range_xor(i64 %a) {
+; CHECK-LABEL: define i1 @constant_range_xor(
+; CHECK-SAME: i64 [[A:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i64 [[A]], 8192
+; CHECK-NEXT:    br i1 [[CMP]], label [[THEN:%.*]], label [[ELSE:%.*]]
+; CHECK:       then:
+; CHECK-NEXT:    [[CTLZ:%.*]] = call i64 @llvm.ctlz.i64(i64 [[A]], i1 true)
+; CHECK-NEXT:    [[CONV:%.*]] = xor i64 [[CTLZ]], 63
+; CHECK-NEXT:    ret i1 false
+; CHECK:       else:
+; CHECK-NEXT:    ret i1 false
+;
+entry:
+  %cmp = icmp ugt i64 %a, 8192
+  br i1 %cmp, label %then, label %else
+then:
+  %ctlz = call i64 @llvm.ctlz.i64(i64 %a, i1 true) ;[0, 50]
+  %conv = xor i64 %ctlz, 63                        ;[13, 63]
+  %cmp1 = icmp ult i64 %conv, 13
+  ret i1 %cmp1
+else:
+  ret i1 false
+}
+
+define i1 @constant_range_xor_negative(i64 %a) {
+; CHECK-LABEL: define i1 @constant_range_xor_negative(
+; CHECK-SAME: i64 [[A:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ugt i64 [[A]], 8192
+; CHECK-NEXT:    br i1 [[CMP]], label [[THEN:%.*]], label [[ELSE:%.*]]
+; CHECK:       then:
+; CHECK-NEXT:    [[CTLZ:%.*]] = call i64 @llvm.ctlz.i64(i64 [[A]], i1 true)
+; CHECK-NEXT:    [[CONV:%.*]] = xor i64 [[CTLZ]], 62
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp ult i64 [[CONV]], 13
+; CHECK-NEXT:    ret i1 [[CMP1]]
+; CHECK:       else:
+; CHECK-NEXT:    ret i1 false
+;
+entry:
+  %cmp = icmp ugt i64 %a, 8192
+  br i1 %cmp, label %then, label %else
+then:
+  %ctlz = call i64 @llvm.ctlz.i64(i64 %a, i1 true) ;[0, 50]
+  %conv = xor i64 %ctlz, 62                        ;[12, 63]
+  %cmp1 = icmp ult i64 %conv, 13
+  ret i1 %cmp1
+else:
+  ret i1 false
+}
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XChy wrote:

If I reason correctly, when both LHS and RHS are consecutive ranges with multiple elements, their KnownBits can't be the subset of that of the other, since the first bit of them is unknown. Thus, we just need more tests with `A xor C`, where `A` can be `and %a, 62` or other variants, and `C` is an appropriate constant.

https://github.com/llvm/llvm-project/pull/80146