[InstCombine] Drop samesign flags in foldLogOpOfMaskedICmps_NotAllZeros_BMask_Mixed
#120373
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
llvmbot
added
llvm:instcombine
|
@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
+}
|
This was referenced Dec 18, 2024
nikic
approved these changes
Dec 18, 2024
|
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
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Counterexamples: https://alive2.llvm.org/ce/z/6Ks8Qz
Closes #120361.