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@llvm/pr-subscribers-llvm-analysis

@llvm/pr-subscribers-llvm-transforms

Author: Bobby SONG (bobby-b-song)

define i1 @<!-- -->src(i32 %0, i32 %1) local_unnamed_addr #<!-- -->0 {
common.ret:
  %2 = xor i32 %0, -1
  %3 = icmp ule i32 %1, %2
  %4 = xor i32 %1, -1
  %5 = icmp ugt i32 %0, %4
  %common.ret.op = and i1 %3, %5
  ret i1 %common.ret.op
}

define noundef i1 @<!-- -->tgt(i32 %0, i32 %1) local_unnamed_addr #<!-- -->0 {
common.ret:
  ret i1 false
}

diff --git a/llvm/test/Transforms/InstCombine/and-comparison-not-always-false.ll b/llvm/test/Transforms/InstCombine/and-comparison-not-always-false.ll
new file mode 100644
index 0000000000000..174d97d30bcf8
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/and-comparison-not-always-false.ll
@@ -0,0 +1,21 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+define i1 @test(i32 %0, i32 %1) {
+; CHECK-LABEL: define i1 @test(
+; CHECK-SAME: i32 [[TMP0:%.*]], i32 [[TMP1:%.*]]) {
+; CHECK-NEXT:  [[COMMON_RET:.*:]]
+; CHECK-NEXT:    [[TMP2:%.*]] = xor i32 [[TMP0]], -1
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp ule i32 [[TMP1]], [[TMP2]]
+; CHECK-NEXT:    [[TMP4:%.*]] = xor i32 [[TMP1]], -1
+; CHECK-NEXT:    [[TMP5:%.*]] = icmp ugt i32 [[TMP0]], [[TMP4]]
+; CHECK-NEXT:    [[COMMON_RET_OP:%.*]] = and i1 [[TMP3]], [[TMP5]]
+; CHECK-NEXT:    ret i1 [[COMMON_RET_OP]]
+;
+common.ret:
+  %2 = xor i32 %0, -1
+  %3 = icmp ule i32 %1, %2
+  %4 = xor i32 %1, -1
+  %5 = icmp ugt i32 %0, %4
+  %common.ret.op = and i1 %3, %5
+  ret i1 %common.ret.op
+}

I've further extended the PR with signed numbers and more inclusive/exclusive ranges, the proof of alive2 is at https://alive2.llvm.org/ce/z/z2VcMn.

As I commented in #141479 (comment), both LHS and RHS are uadd-overflow check idiom. I am not sure if it is profitable to canonicalize them into extractvalue uadd.overflow(x, y), 1. If not, we can add a helper function to recognize such overflow-checking patterns. cc @nikic @AZero13

As I commented in #141479 (comment), both LHS and RHS are uadd-overflow check idiom. I am not sure if it is profitable to canonicalize them into extractvalue uadd.overflow(x, y), 1. If not, we can add a helper function to recognize such overflow-checking patterns.

We have m_UAddWithOverflow() for this. It does match the ~x < y pattern as well. But it doesn't match the negated overflow check.