[InstCombine] Drop samesign flags in foldLogOpOfMaskedICmps_NotAllZeros_BMask_Mixed#120373
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@llvm/pr-subscribers-llvm-transforms Author: Yingwei Zheng (dtcxzyw) ChangesCounterexamples: https://alive2.llvm.org/ce/z/6Ks8Qz Full diff: https://github.com/llvm/llvm-project/pull/120373.diff 2 Files Affected:
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index dff9304be64ddb..e576eea4ca36a1 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -455,14 +455,20 @@ static Value *foldLogOpOfMaskedICmps_NotAllZeros_BMask_Mixed(
// RHS. For example,
// (icmp ne (A & 255), 0) & (icmp eq (A & 15), 8) -> (icmp eq (A & 15), 8).
// (icmp ne (A & 15), 0) & (icmp eq (A & 15), 8) -> (icmp eq (A & 15), 8).
- if (IsSuperSetOrEqual(BCst, DCst))
+ if (IsSuperSetOrEqual(BCst, DCst)) {
+ // We can't guarantee that samesign hold after this fold.
+ RHS->setSameSign(false);
return RHS;
+ }
// Otherwise, B is a subset of D. If B and E have a common bit set,
// ie. (B & E) != 0, then LHS is subsumed by RHS. For example.
// (icmp ne (A & 12), 0) & (icmp eq (A & 15), 8) -> (icmp eq (A & 15), 8).
assert(IsSubSetOrEqual(BCst, DCst) && "Precondition due to above code");
- if ((*BCst & ECst) != 0)
+ if ((*BCst & ECst) != 0) {
+ // We can't guarantee that samesign hold after this fold.
+ RHS->setSameSign(false);
return RHS;
+ }
// Otherwise, LHS and RHS contradict and the whole expression becomes false
// (or true if negated.) For example,
// (icmp ne (A & 7), 0) & (icmp eq (A & 15), 8) -> false.
diff --git a/llvm/test/Transforms/InstCombine/icmp-logical.ll b/llvm/test/Transforms/InstCombine/icmp-logical.ll
index 50feb51092fd9e..df8442e069b788 100644
--- a/llvm/test/Transforms/InstCombine/icmp-logical.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-logical.ll
@@ -1900,3 +1900,28 @@ define i1 @masked_icmps_bmask_notmixed_not_subset_notoptimized(i32 %A) {
%res = and i1 %tst1, %tst2
ret i1 %res
}
+
+define i1 @pr120361(i8 %x, i8 %y) {
+; CHECK-LABEL: @pr120361(
+; CHECK-NEXT: [[CMP1:%.*]] = icmp eq i8 [[X:%.*]], -1
+; CHECK-NEXT: ret i1 [[CMP1]]
+;
+ %cmp1 = icmp samesign eq i8 %x, -1
+ %cmp2 = icmp ne i8 %x, 0
+ %result = select i1 %cmp2, i1 %cmp1, i1 false
+ ret i1 %result
+}
+
+define i1 @pr120361_v2(i32 %x) {
+; CHECK-LABEL: @pr120361_v2(
+; CHECK-NEXT: [[AND2:%.*]] = and i32 [[X:%.*]], -113
+; CHECK-NEXT: [[CMP2:%.*]] = icmp eq i32 [[AND2]], 15
+; CHECK-NEXT: ret i1 [[CMP2]]
+;
+ %and1 = and i32 %x, 15
+ %cmp1 = icmp ne i32 %and1, 0
+ %and2 = and i32 %x, -113
+ %cmp2 = icmp samesign eq i32 %and2, 15
+ %and = select i1 %cmp1, i1 %cmp2, i1 false
+ ret i1 %and
+}
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This was referenced Dec 18, 2024
nikic
approved these changes
Dec 18, 2024
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/30/builds/12533 Here is the relevant piece of the build log for the reference |
This was referenced Jun 2, 2025
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Counterexamples: https://alive2.llvm.org/ce/z/6Ks8Qz
Closes #120361.