[llvm] [LAA] Fix non-NFC parts of 1aded51 (PR #160701)

[Ramkumar Ramachandra via llvm-commits]

https://github.com/artagnon created https://github.com/llvm/llvm-project/pull/160701

1aded51 ([LAA] Prepare to handle diff type sizes (NFC)) was supposed to be a non-functional patch, but introduced functional changes as known-non-negative and known-non-positive is not equivalent to !known-non-zero. Fix this.

>From eeb73a9e6ebd0a88874d0508406b8e24307f6d83 Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Thu, 25 Sep 2025 12:47:30 +0100
Subject: [PATCH 1/2] [LAA] Pre-commit test for possibly-zero-dist-diff-typesz

---
 .../LoopAccessAnalysis/depend_diff_types.ll   | 46 +++++++++++++++++++
 1 file changed, 46 insertions(+)

diff --git a/llvm/test/Analysis/LoopAccessAnalysis/depend_diff_types.ll b/llvm/test/Analysis/LoopAccessAnalysis/depend_diff_types.ll
index 023a8c056968f..840fe915e0570 100644
--- a/llvm/test/Analysis/LoopAccessAnalysis/depend_diff_types.ll
+++ b/llvm/test/Analysis/LoopAccessAnalysis/depend_diff_types.ll
@@ -187,6 +187,52 @@ exit:
   ret void
 }
 
+; In the following test, dependence distance is possibly zero,
+; but this is not equivalent to the condition known-non-positive
+; and known-non-negative.
+
+define void @possibly_zero_dist_diff_typesz(ptr %p) {
+; CHECK-LABEL: 'possibly_zero_dist_diff_typesz'
+; CHECK-NEXT:    loop:
+; CHECK-NEXT:      Memory dependences are safe with run-time checks
+; CHECK-NEXT:      Dependences:
+; CHECK-NEXT:      Run-time memory checks:
+; CHECK-NEXT:      Check 0:
+; CHECK-NEXT:        Comparing group GRP0:
+; CHECK-NEXT:          %gep.p.iv.i16 = getelementptr inbounds nuw i16, ptr %p, i16 %iv
+; CHECK-NEXT:        Against group GRP1:
+; CHECK-NEXT:          %gep.p.iv.i32 = getelementptr inbounds nuw i32, ptr %p, i16 %iv
+; CHECK-NEXT:      Grouped accesses:
+; CHECK-NEXT:        Group GRP0:
+; CHECK-NEXT:          (Low: %p High: (64 + %p))
+; CHECK-NEXT:            Member: {%p,+,2}<nuw><%loop>
+; CHECK-NEXT:        Group GRP1:
+; CHECK-NEXT:          (Low: %p High: (128 + %p))
+; CHECK-NEXT:            Member: {%p,+,4}<nuw><%loop>
+; CHECK-EMPTY:
+; CHECK-NEXT:      Non vectorizable stores to invariant address were not found in loop.
+; CHECK-NEXT:      SCEV assumptions:
+; CHECK-EMPTY:
+; CHECK-NEXT:      Expressions re-written:
+;
+entry:
+  br label %loop
+
+loop:
+  %iv = phi i16 [ 0, %entry ], [ %iv.next, %loop ]
+  %gep.p.iv.i32 = getelementptr inbounds nuw i32, ptr %p, i16 %iv
+  %ld.p = load i32, ptr %gep.p.iv.i32, align 1
+  %trunc = trunc i32 %ld.p to i16
+  %gep.p.iv.i16 = getelementptr inbounds nuw i16, ptr %p, i16 %iv
+  store i16 %trunc, ptr %gep.p.iv.i16, align 1
+  %iv.next = add nuw nsw i16 %iv, 1
+  %exit.cond = icmp eq i16 %iv.next, 32
+  br i1 %exit.cond, label %exit, label %loop
+
+exit:
+  ret void
+}
+
 ; In the following test, the sink is loop-invariant.
 
 define void @type_size_equivalence_sink_loopinv(ptr nocapture %vec, i64 %n) {

>From 55811d76c7fb7c5a78de547852d305b8c1fd3939 Mon Sep 17 00:00:00 2001
From: Ramkumar Ramachandra <ramkumar.ramachandra at codasip.com>
Date: Thu, 25 Sep 2025 12:50:14 +0100
Subject: [PATCH 2/2] [LAA] Fix non-NFC parts of 1aded51

1aded51 ([LAA] Prepare to handle diff type sizes (NFC)) was supposed to
be a non-functional patch, but introduced functional changes as
known-non-negative and known-non-positive is not equivalent to
!known-non-zero. Fix this.
---
 llvm/lib/Analysis/LoopAccessAnalysis.cpp        |  3 ++-
 .../LoopAccessAnalysis/depend_diff_types.ll     | 17 +++++------------
 2 files changed, 7 insertions(+), 13 deletions(-)

diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index d6ad855cad9a7..512ae415d1c3b 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -2122,7 +2122,8 @@ MemoryDepChecker::getDependenceDistanceStrideAndSize(
   // dependence.
   TypeSize AStoreSz = DL.getTypeStoreSize(ATy);
   TypeSize BStoreSz = DL.getTypeStoreSize(BTy);
-  if (AStoreSz != BStoreSz && !SE.isKnownNonZero(Dist)) {
+  if (AStoreSz != BStoreSz && SE.isKnownNonPositive(Dist) &&
+      SE.isKnownNonNegative(Dist)) {
     LLVM_DEBUG(dbgs() << "LAA: possibly zero dependence distance with "
                          "different type sizes\n");
     return Dependence::Unknown;
diff --git a/llvm/test/Analysis/LoopAccessAnalysis/depend_diff_types.ll b/llvm/test/Analysis/LoopAccessAnalysis/depend_diff_types.ll
index 840fe915e0570..c367b31f6d445 100644
--- a/llvm/test/Analysis/LoopAccessAnalysis/depend_diff_types.ll
+++ b/llvm/test/Analysis/LoopAccessAnalysis/depend_diff_types.ll
@@ -194,21 +194,14 @@ exit:
 define void @possibly_zero_dist_diff_typesz(ptr %p) {
 ; CHECK-LABEL: 'possibly_zero_dist_diff_typesz'
 ; CHECK-NEXT:    loop:
-; CHECK-NEXT:      Memory dependences are safe with run-time checks
+; CHECK-NEXT:      Memory dependences are safe
 ; CHECK-NEXT:      Dependences:
+; CHECK-NEXT:        Forward:
+; CHECK-NEXT:            %ld.p = load i32, ptr %gep.p.iv.i32, align 1 ->
+; CHECK-NEXT:            store i16 %trunc, ptr %gep.p.iv.i16, align 1
+; CHECK-EMPTY:
 ; CHECK-NEXT:      Run-time memory checks:
-; CHECK-NEXT:      Check 0:
-; CHECK-NEXT:        Comparing group GRP0:
-; CHECK-NEXT:          %gep.p.iv.i16 = getelementptr inbounds nuw i16, ptr %p, i16 %iv
-; CHECK-NEXT:        Against group GRP1:
-; CHECK-NEXT:          %gep.p.iv.i32 = getelementptr inbounds nuw i32, ptr %p, i16 %iv
 ; CHECK-NEXT:      Grouped accesses:
-; CHECK-NEXT:        Group GRP0:
-; CHECK-NEXT:          (Low: %p High: (64 + %p))
-; CHECK-NEXT:            Member: {%p,+,2}<nuw><%loop>
-; CHECK-NEXT:        Group GRP1:
-; CHECK-NEXT:          (Low: %p High: (128 + %p))
-; CHECK-NEXT:            Member: {%p,+,4}<nuw><%loop>
 ; CHECK-EMPTY:
 ; CHECK-NEXT:      Non vectorizable stores to invariant address were not found in loop.
 ; CHECK-NEXT:      SCEV assumptions: