[llvm] [ValueTracking] Analyze `Select` in `isKnownNonEqual`. (PR #68427)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

<details>
<summary>Changes</summary>

Basic way to recursively analyze `select` in `isKnownNonEqual`: `select %c, %t, %f` is non-equal to `%x` if `%t` is non-equal to `%x` and `%f` is non-equal to `%x`.

---
Full diff: https://github.com/llvm/llvm-project/pull/68427.diff


2 Files Affected:

- (modified) llvm/lib/Analysis/ValueTracking.cpp (+20) 
- (added) llvm/test/Analysis/BasicAA/non-equal-select.ll (+33) 


``````````diff
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 3af5a6d9a167de4..1c284e8d85ca417 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -3112,6 +3112,23 @@ static bool isNonEqualPHIs(const PHINode *PN1, const PHINode *PN2,
   return true;
 }
 
+static bool isNonEqualSELECT(const Value *V1, const Value *V2, unsigned Depth,
+                             const SimplifyQuery &Q) {
+  const SelectInst *SI1 = dyn_cast<SelectInst>(V1);
+  if (!SI1)
+    return false;
+
+  if (const SelectInst *SI2 = dyn_cast<SelectInst>(V2)) {
+    if (SI1->getCondition() == SI2->getCondition())
+      return isKnownNonEqual(SI1->getTrueValue(), SI2->getTrueValue(),
+                             Depth + 1, Q) &&
+             isKnownNonEqual(SI1->getFalseValue(), SI2->getFalseValue(),
+                             Depth + 1, Q);
+  }
+  return isKnownNonEqual(SI1->getTrueValue(), V2, Depth + 1, Q) &&
+         isKnownNonEqual(SI1->getFalseValue(), V2, Depth + 1, Q);
+}
+
 /// Return true if it is known that V1 != V2.
 static bool isKnownNonEqual(const Value *V1, const Value *V2, unsigned Depth,
                             const SimplifyQuery &Q) {
@@ -3142,6 +3159,9 @@ static bool isKnownNonEqual(const Value *V1, const Value *V2, unsigned Depth,
     };
   }
 
+  if (isNonEqualSELECT(V1, V2, Depth, Q) || isNonEqualSELECT(V2, V1, Depth, Q))
+    return true;
+
   if (isAddOfNonZero(V1, V2, Depth, Q) || isAddOfNonZero(V2, V1, Depth, Q))
     return true;
 
diff --git a/llvm/test/Analysis/BasicAA/non-equal-select.ll b/llvm/test/Analysis/BasicAA/non-equal-select.ll
new file mode 100644
index 000000000000000..1af37245c6d85a6
--- /dev/null
+++ b/llvm/test/Analysis/BasicAA/non-equal-select.ll
@@ -0,0 +1,33 @@
+; RUN: opt < %s -aa-pipeline=basic-aa -passes=aa-eval -print-all-alias-modref-info -disable-output 2>&1 | FileCheck %s
+ at G = global [10 x i32] zeroinitializer, align 4
+
+; Function Attrs: mustprogress nofree norecurse nosync nounwind willreturn memory(readwrite, argmem: none, inaccessiblemem: none) uwtable
+define void @select_in_gep1(i1 %c, i64 noundef %x) {
+entry:
+; CHECK: Function: select_in_gep1
+; CHECK: NoAlias: i32* %arrayidx1, i32* %arrayidx2
+  %add1_ = add nsw i64 %x, 1
+  %add2_ = add nsw i64 %x, 2
+  %select_ = select i1 %c, i64 %add1_, i64 %add2_
+  %arrayidx1 = getelementptr inbounds [10 x i32], ptr @G, i64 0, i64 %select_
+  store i32 42, ptr %arrayidx1, align 4
+  %arrayidx2 = getelementptr inbounds [10 x i32], ptr @G, i64 0, i64 %x
+  store i32 43, ptr %arrayidx2, align 4
+  ret void
+}
+
+define void @select_in_gep2(i1 %c, i64 noundef %x) {
+entry:
+  ; TODO: should be "NoAlias" here as well.
+; CHECK: Function: select_in_gep2
+; CHECK: MayAlias:     i32* %arrayidx1, i32* %arrayidx2
+  %add1_ = add nsw i64 %x, 1
+  %add2_ = add nsw i64 %x, 2
+  %add3_ = add nsw i64 %x, 3
+  %select_ = select i1 %c, i64 %add1_, i64 %add2_
+  %arrayidx1 = getelementptr inbounds [10 x i32], ptr @G, i64 0, i64 %select_
+  store i32 42, ptr %arrayidx1, align 4
+  %arrayidx2 = getelementptr inbounds [10 x i32], ptr @G, i64 0, i64 %add3_
+  store i32 43, ptr %arrayidx2, align 4
+  ret void
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/68427