[HashRecognize] Forbid optz when data.next has exit-block user #165574
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
The CRC optimization relies on stripping the auxiliary data completely, and should hence be forbidden when it has a user in the exit-block. Forbid this case, fixing a miscompile. Fixes llvm#165382.
pfusik
reviewed
Oct 29, 2025
llvmbot
added
llvm:analysis
|
@llvm/pr-subscribers-llvm-analysis Author: Ramkumar Ramachandra (artagnon) ChangesThe CRC optimization relies on stripping the auxiliary data completely, and should hence be forbidden when it has a user in the exit-block. Forbid this case, fixing a miscompile. Fixes #165382. Full diff: https://github.com/llvm/llvm-project/pull/165574.diff 3 Files Affected:
diff --git a/llvm/lib/Analysis/HashRecognize.cpp b/llvm/lib/Analysis/HashRecognize.cpp
index 4529123508a7c..9fddb57effd4f 100644
--- a/llvm/lib/Analysis/HashRecognize.cpp
+++ b/llvm/lib/Analysis/HashRecognize.cpp
@@ -487,6 +487,14 @@ std::variant<PolynomialInfo, StringRef> HashRecognize::recognizeCRC() const {
: LHS->getType()->getIntegerBitWidth()))
return "Loop iterations exceed bitwidth of data";
+ // Make sure that the simple recurrence evolution isn't used in the exit
+ // block.
+ if (SimpleRecurrence && any_of(SimpleRecurrence.BO->users(), [Exit](User *U) {
+ auto *UI = dyn_cast<Instruction>(U);
+ return UI && UI->getParent() == Exit;
+ }))
+ return "Recurrences have stray uses";
+
// Make sure that the computed value is used in the exit block: this should be
// true even if it is only really used in an outer loop's exit block, since
// the loop is in LCSSA form.
diff --git a/llvm/test/Analysis/HashRecognize/cyclic-redundancy-check.ll b/llvm/test/Analysis/HashRecognize/cyclic-redundancy-check.ll
index 7dec2f8f96906..78b4139d21982 100644
--- a/llvm/test/Analysis/HashRecognize/cyclic-redundancy-check.ll
+++ b/llvm/test/Analysis/HashRecognize/cyclic-redundancy-check.ll
@@ -1448,4 +1448,85 @@ exit: ; preds = %loop
ret i16 %crc.next
}
+define i16 @not.crc.data.next.outside.user(i16 %crc.init, i16 %data.init) {
+; CHECK-LABEL: 'not.crc.data.next.outside.user'
+; CHECK-NEXT: Did not find a hash algorithm
+; CHECK-NEXT: Reason: Recurrences have stray uses
+;
+entry:
+ br label %loop
+
+loop:
+ %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
+ %crc = phi i16 [ %crc.init, %entry ], [ %crc.next, %loop ]
+ %data = phi i16 [ %data.init, %entry ], [ %data.next, %loop ]
+ %xor.crc.data = xor i16 %data, %crc
+ %crc.shl = shl i16 %crc, 1
+ %crc.xor = xor i16 %crc.shl, 3
+ %check.sb = icmp slt i16 %xor.crc.data, 0
+ %crc.next = select i1 %check.sb, i16 %crc.xor, i16 %crc.shl
+ %data.next = shl i16 %data, 1
+ %iv.next = add nuw nsw i32 %iv, 1
+ %exit.cond = icmp samesign ult i32 %iv, 7
+ br i1 %exit.cond, label %loop, label %exit
+
+exit:
+ %ret = xor i16 %data.next, %crc.next
+ ret i16 %ret
+}
+
+define i16 @not.crc.data.phi.outside.user(i16 %crc.init, i16 %data.init) {
+; CHECK-LABEL: 'not.crc.data.phi.outside.user'
+; CHECK-NEXT: Did not find a hash algorithm
+; CHECK-NEXT: Reason: Recurrences have stray uses
+;
+entry:
+ br label %loop
+
+loop:
+ %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
+ %crc = phi i16 [ %crc.init, %entry ], [ %crc.next, %loop ]
+ %data = phi i16 [ %data.init, %entry ], [ %data.next, %loop ]
+ %xor.crc.data = xor i16 %data, %crc
+ %crc.shl = shl i16 %crc, 1
+ %crc.xor = xor i16 %crc.shl, 3
+ %check.sb = icmp slt i16 %xor.crc.data, 0
+ %crc.next = select i1 %check.sb, i16 %crc.xor, i16 %crc.shl
+ %data.next = shl i16 %data, 1
+ %iv.next = add nuw nsw i32 %iv, 1
+ %exit.cond = icmp samesign ult i32 %iv, 7
+ br i1 %exit.cond, label %loop, label %exit
+
+exit:
+ %ret = xor i16 %data, %crc.next
+ ret i16 %ret
+}
+
+define i16 @not.crc.crc.phi.outside.user(i16 %crc.init, i16 %data.init) {
+; CHECK-LABEL: 'not.crc.crc.phi.outside.user'
+; CHECK-NEXT: Did not find a hash algorithm
+; CHECK-NEXT: Reason: Recurrences have stray uses
+;
+entry:
+ br label %loop
+
+loop:
+ %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
+ %crc = phi i16 [ %crc.init, %entry ], [ %crc.next, %loop ]
+ %data = phi i16 [ %data.init, %entry ], [ %data.next, %loop ]
+ %xor.crc.data = xor i16 %data, %crc
+ %crc.shl = shl i16 %crc, 1
+ %crc.xor = xor i16 %crc.shl, 3
+ %check.sb = icmp slt i16 %xor.crc.data, 0
+ %crc.next = select i1 %check.sb, i16 %crc.xor, i16 %crc.shl
+ %data.next = shl i16 %data, 1
+ %iv.next = add nuw nsw i32 %iv, 1
+ %exit.cond = icmp samesign ult i32 %iv, 7
+ br i1 %exit.cond, label %loop, label %exit
+
+exit:
+ %ret = xor i16 %crc, %crc.next
+ ret i16 %ret
+}
+
declare i16 @side.effect()
diff --git a/llvm/test/Transforms/LoopIdiom/cyclic-redundancy-check.ll b/llvm/test/Transforms/LoopIdiom/cyclic-redundancy-check.ll
index b2ec53ca405d4..90995a0257721 100644
--- a/llvm/test/Transforms/LoopIdiom/cyclic-redundancy-check.ll
+++ b/llvm/test/Transforms/LoopIdiom/cyclic-redundancy-check.ll
@@ -537,6 +537,52 @@ exit: ; preds = %loop
%ret = and i32 %unrelated.next, %crc.next
ret i32 %ret
}
+
+define i16 @not.crc.data.next.outside.user(i16 %crc.init, i16 %data.init) {
+; CHECK-LABEL: define i16 @not.crc.data.next.outside.user(
+; CHECK-SAME: i16 [[CRC_INIT:%.*]], i16 [[DATA_INIT:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*]]:
+; CHECK-NEXT: br label %[[LOOP:.*]]
+; CHECK: [[LOOP]]:
+; CHECK-NEXT: [[IV:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
+; CHECK-NEXT: [[TBL_LD:%.*]] = phi i16 [ [[CRC_INIT]], %[[ENTRY]] ], [ [[CRC_NEXT:%.*]], %[[LOOP]] ]
+; CHECK-NEXT: [[CRC_BE_SHIFT:%.*]] = phi i16 [ [[DATA_INIT]], %[[ENTRY]] ], [ [[DATA_NEXT:%.*]], %[[LOOP]] ]
+; CHECK-NEXT: [[CRC_NEXT3:%.*]] = xor i16 [[CRC_BE_SHIFT]], [[TBL_LD]]
+; CHECK-NEXT: [[CRC_SHL:%.*]] = shl i16 [[TBL_LD]], 1
+; CHECK-NEXT: [[CRC_XOR:%.*]] = xor i16 [[CRC_SHL]], 3
+; CHECK-NEXT: [[CHECK_SB:%.*]] = icmp slt i16 [[CRC_NEXT3]], 0
+; CHECK-NEXT: [[CRC_NEXT]] = select i1 [[CHECK_SB]], i16 [[CRC_XOR]], i16 [[CRC_SHL]]
+; CHECK-NEXT: [[DATA_NEXT]] = shl i16 [[CRC_BE_SHIFT]], 1
+; CHECK-NEXT: [[IV_NEXT]] = add nuw nsw i32 [[IV]], 1
+; CHECK-NEXT: [[EXIT_COND:%.*]] = icmp samesign ult i32 [[IV]], 7
+; CHECK-NEXT: br i1 [[EXIT_COND]], label %[[LOOP]], label %[[EXIT:.*]]
+; CHECK: [[EXIT]]:
+; CHECK-NEXT: [[CRC_NEXT_LCSSA:%.*]] = phi i16 [ [[CRC_NEXT]], %[[LOOP]] ]
+; CHECK-NEXT: [[DATA_NEXT_LCSSA:%.*]] = phi i16 [ [[DATA_NEXT]], %[[LOOP]] ]
+; CHECK-NEXT: [[RET:%.*]] = xor i16 [[DATA_NEXT_LCSSA]], [[CRC_NEXT_LCSSA]]
+; CHECK-NEXT: ret i16 [[RET]]
+;
+entry:
+ br label %loop
+
+loop:
+ %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
+ %crc = phi i16 [ %crc.init, %entry ], [ %crc.next, %loop ]
+ %data = phi i16 [ %data.init, %entry ], [ %data.next, %loop ]
+ %xor.crc.data = xor i16 %data, %crc
+ %crc.shl = shl i16 %crc, 1
+ %crc.xor = xor i16 %crc.shl, 3
+ %check.sb = icmp slt i16 %xor.crc.data, 0
+ %crc.next = select i1 %check.sb, i16 %crc.xor, i16 %crc.shl
+ %data.next = shl i16 %data, 1
+ %iv.next = add nuw nsw i32 %iv, 1
+ %exit.cond = icmp samesign ult i32 %iv, 7
+ br i1 %exit.cond, label %loop, label %exit
+
+exit:
+ %ret = xor i16 %data.next, %crc.next
+ ret i16 %ret
+}
;.
; CHECK: attributes #[[ATTR0]] = { optsize }
;.
|
|
@llvm/pr-subscribers-llvm-transforms Author: Ramkumar Ramachandra (artagnon) ChangesThe CRC optimization relies on stripping the auxiliary data completely, and should hence be forbidden when it has a user in the exit-block. Forbid this case, fixing a miscompile. Fixes #165382. Full diff: https://github.com/llvm/llvm-project/pull/165574.diff 3 Files Affected:
diff --git a/llvm/lib/Analysis/HashRecognize.cpp b/llvm/lib/Analysis/HashRecognize.cpp
index 4529123508a7c..9fddb57effd4f 100644
--- a/llvm/lib/Analysis/HashRecognize.cpp
+++ b/llvm/lib/Analysis/HashRecognize.cpp
@@ -487,6 +487,14 @@ std::variant<PolynomialInfo, StringRef> HashRecognize::recognizeCRC() const {
: LHS->getType()->getIntegerBitWidth()))
return "Loop iterations exceed bitwidth of data";
+ // Make sure that the simple recurrence evolution isn't used in the exit
+ // block.
+ if (SimpleRecurrence && any_of(SimpleRecurrence.BO->users(), [Exit](User *U) {
+ auto *UI = dyn_cast<Instruction>(U);
+ return UI && UI->getParent() == Exit;
+ }))
+ return "Recurrences have stray uses";
+
// Make sure that the computed value is used in the exit block: this should be
// true even if it is only really used in an outer loop's exit block, since
// the loop is in LCSSA form.
diff --git a/llvm/test/Analysis/HashRecognize/cyclic-redundancy-check.ll b/llvm/test/Analysis/HashRecognize/cyclic-redundancy-check.ll
index 7dec2f8f96906..78b4139d21982 100644
--- a/llvm/test/Analysis/HashRecognize/cyclic-redundancy-check.ll
+++ b/llvm/test/Analysis/HashRecognize/cyclic-redundancy-check.ll
@@ -1448,4 +1448,85 @@ exit: ; preds = %loop
ret i16 %crc.next
}
+define i16 @not.crc.data.next.outside.user(i16 %crc.init, i16 %data.init) {
+; CHECK-LABEL: 'not.crc.data.next.outside.user'
+; CHECK-NEXT: Did not find a hash algorithm
+; CHECK-NEXT: Reason: Recurrences have stray uses
+;
+entry:
+ br label %loop
+
+loop:
+ %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
+ %crc = phi i16 [ %crc.init, %entry ], [ %crc.next, %loop ]
+ %data = phi i16 [ %data.init, %entry ], [ %data.next, %loop ]
+ %xor.crc.data = xor i16 %data, %crc
+ %crc.shl = shl i16 %crc, 1
+ %crc.xor = xor i16 %crc.shl, 3
+ %check.sb = icmp slt i16 %xor.crc.data, 0
+ %crc.next = select i1 %check.sb, i16 %crc.xor, i16 %crc.shl
+ %data.next = shl i16 %data, 1
+ %iv.next = add nuw nsw i32 %iv, 1
+ %exit.cond = icmp samesign ult i32 %iv, 7
+ br i1 %exit.cond, label %loop, label %exit
+
+exit:
+ %ret = xor i16 %data.next, %crc.next
+ ret i16 %ret
+}
+
+define i16 @not.crc.data.phi.outside.user(i16 %crc.init, i16 %data.init) {
+; CHECK-LABEL: 'not.crc.data.phi.outside.user'
+; CHECK-NEXT: Did not find a hash algorithm
+; CHECK-NEXT: Reason: Recurrences have stray uses
+;
+entry:
+ br label %loop
+
+loop:
+ %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
+ %crc = phi i16 [ %crc.init, %entry ], [ %crc.next, %loop ]
+ %data = phi i16 [ %data.init, %entry ], [ %data.next, %loop ]
+ %xor.crc.data = xor i16 %data, %crc
+ %crc.shl = shl i16 %crc, 1
+ %crc.xor = xor i16 %crc.shl, 3
+ %check.sb = icmp slt i16 %xor.crc.data, 0
+ %crc.next = select i1 %check.sb, i16 %crc.xor, i16 %crc.shl
+ %data.next = shl i16 %data, 1
+ %iv.next = add nuw nsw i32 %iv, 1
+ %exit.cond = icmp samesign ult i32 %iv, 7
+ br i1 %exit.cond, label %loop, label %exit
+
+exit:
+ %ret = xor i16 %data, %crc.next
+ ret i16 %ret
+}
+
+define i16 @not.crc.crc.phi.outside.user(i16 %crc.init, i16 %data.init) {
+; CHECK-LABEL: 'not.crc.crc.phi.outside.user'
+; CHECK-NEXT: Did not find a hash algorithm
+; CHECK-NEXT: Reason: Recurrences have stray uses
+;
+entry:
+ br label %loop
+
+loop:
+ %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
+ %crc = phi i16 [ %crc.init, %entry ], [ %crc.next, %loop ]
+ %data = phi i16 [ %data.init, %entry ], [ %data.next, %loop ]
+ %xor.crc.data = xor i16 %data, %crc
+ %crc.shl = shl i16 %crc, 1
+ %crc.xor = xor i16 %crc.shl, 3
+ %check.sb = icmp slt i16 %xor.crc.data, 0
+ %crc.next = select i1 %check.sb, i16 %crc.xor, i16 %crc.shl
+ %data.next = shl i16 %data, 1
+ %iv.next = add nuw nsw i32 %iv, 1
+ %exit.cond = icmp samesign ult i32 %iv, 7
+ br i1 %exit.cond, label %loop, label %exit
+
+exit:
+ %ret = xor i16 %crc, %crc.next
+ ret i16 %ret
+}
+
declare i16 @side.effect()
diff --git a/llvm/test/Transforms/LoopIdiom/cyclic-redundancy-check.ll b/llvm/test/Transforms/LoopIdiom/cyclic-redundancy-check.ll
index b2ec53ca405d4..90995a0257721 100644
--- a/llvm/test/Transforms/LoopIdiom/cyclic-redundancy-check.ll
+++ b/llvm/test/Transforms/LoopIdiom/cyclic-redundancy-check.ll
@@ -537,6 +537,52 @@ exit: ; preds = %loop
%ret = and i32 %unrelated.next, %crc.next
ret i32 %ret
}
+
+define i16 @not.crc.data.next.outside.user(i16 %crc.init, i16 %data.init) {
+; CHECK-LABEL: define i16 @not.crc.data.next.outside.user(
+; CHECK-SAME: i16 [[CRC_INIT:%.*]], i16 [[DATA_INIT:%.*]]) {
+; CHECK-NEXT: [[ENTRY:.*]]:
+; CHECK-NEXT: br label %[[LOOP:.*]]
+; CHECK: [[LOOP]]:
+; CHECK-NEXT: [[IV:%.*]] = phi i32 [ 0, %[[ENTRY]] ], [ [[IV_NEXT:%.*]], %[[LOOP]] ]
+; CHECK-NEXT: [[TBL_LD:%.*]] = phi i16 [ [[CRC_INIT]], %[[ENTRY]] ], [ [[CRC_NEXT:%.*]], %[[LOOP]] ]
+; CHECK-NEXT: [[CRC_BE_SHIFT:%.*]] = phi i16 [ [[DATA_INIT]], %[[ENTRY]] ], [ [[DATA_NEXT:%.*]], %[[LOOP]] ]
+; CHECK-NEXT: [[CRC_NEXT3:%.*]] = xor i16 [[CRC_BE_SHIFT]], [[TBL_LD]]
+; CHECK-NEXT: [[CRC_SHL:%.*]] = shl i16 [[TBL_LD]], 1
+; CHECK-NEXT: [[CRC_XOR:%.*]] = xor i16 [[CRC_SHL]], 3
+; CHECK-NEXT: [[CHECK_SB:%.*]] = icmp slt i16 [[CRC_NEXT3]], 0
+; CHECK-NEXT: [[CRC_NEXT]] = select i1 [[CHECK_SB]], i16 [[CRC_XOR]], i16 [[CRC_SHL]]
+; CHECK-NEXT: [[DATA_NEXT]] = shl i16 [[CRC_BE_SHIFT]], 1
+; CHECK-NEXT: [[IV_NEXT]] = add nuw nsw i32 [[IV]], 1
+; CHECK-NEXT: [[EXIT_COND:%.*]] = icmp samesign ult i32 [[IV]], 7
+; CHECK-NEXT: br i1 [[EXIT_COND]], label %[[LOOP]], label %[[EXIT:.*]]
+; CHECK: [[EXIT]]:
+; CHECK-NEXT: [[CRC_NEXT_LCSSA:%.*]] = phi i16 [ [[CRC_NEXT]], %[[LOOP]] ]
+; CHECK-NEXT: [[DATA_NEXT_LCSSA:%.*]] = phi i16 [ [[DATA_NEXT]], %[[LOOP]] ]
+; CHECK-NEXT: [[RET:%.*]] = xor i16 [[DATA_NEXT_LCSSA]], [[CRC_NEXT_LCSSA]]
+; CHECK-NEXT: ret i16 [[RET]]
+;
+entry:
+ br label %loop
+
+loop:
+ %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
+ %crc = phi i16 [ %crc.init, %entry ], [ %crc.next, %loop ]
+ %data = phi i16 [ %data.init, %entry ], [ %data.next, %loop ]
+ %xor.crc.data = xor i16 %data, %crc
+ %crc.shl = shl i16 %crc, 1
+ %crc.xor = xor i16 %crc.shl, 3
+ %check.sb = icmp slt i16 %xor.crc.data, 0
+ %crc.next = select i1 %check.sb, i16 %crc.xor, i16 %crc.shl
+ %data.next = shl i16 %data, 1
+ %iv.next = add nuw nsw i32 %iv, 1
+ %exit.cond = icmp samesign ult i32 %iv, 7
+ br i1 %exit.cond, label %loop, label %exit
+
+exit:
+ %ret = xor i16 %data.next, %crc.next
+ ret i16 %ret
+}
;.
; CHECK: attributes #[[ATTR0]] = { optsize }
;.
|
pfusik
reviewed
Oct 29, 2025
aokblast
pushed a commit
to aokblast/llvm-project
that referenced
this pull request
Oct 30, 2025
…165574) The CRC optimization relies on stripping the auxiliary data completely, and should hence be forbidden when it has a user in the exit-block. Forbid this case, fixing a miscompile. Fixes llvm#165382.
DEBADRIBASAK
pushed a commit
to DEBADRIBASAK/llvm-project
that referenced
this pull request
Nov 3, 2025
…165574) The CRC optimization relies on stripping the auxiliary data completely, and should hence be forbidden when it has a user in the exit-block. Forbid this case, fixing a miscompile. Fixes llvm#165382.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 participants
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.
The CRC optimization relies on stripping the auxiliary data completely, and should hence be forbidden when it has a user in the exit-block. Forbid this case, fixing a miscompile.
Fixes #165382.