[ValueTracking] Add support for xor/disjoint or in isKnownNonZero

[goldsteinn]

• [ValueTracking] Add tests for xor/disjoint or in isKnownNonZero; NFC
• [ValueTracking] Add support for xor/disjoint or in isKnownNonZero

Handles cases like X ^ Y == X / X disjoint| Y == X.

Both of these cases have identical logic to the existing add case,
so just converting the add code to a more general helper.

Proofs: https://alive2.llvm.org/ce/z/Htm7pe

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

@llvm/pr-subscribers-llvm-analysis

Author: None (goldsteinn)

Changes

• [ValueTracking] Add tests for xor/disjoint or in isKnownNonZero; NFC
• [ValueTracking] Add support for xor/disjoint or in isKnownNonZero

---

Full diff: https://github.com/llvm/llvm-project/pull/87706.diff

2 Files Affected:

• (modified) llvm/lib/Analysis/ValueTracking.cpp (+27-13)
• (modified) llvm/test/Transforms/InstSimplify/icmp.ll (+60-1)

diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 5ad4da43bca7db..a4b1352b8cea1e 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -3092,20 +3092,33 @@ getInvertibleOperands(const Operator *Op1,
   return std::nullopt;
 }
 
-/// Return true if V2 == V1 + X, where X is known non-zero.
-static bool isAddOfNonZero(const Value *V1, const Value *V2, unsigned Depth,
-                           const SimplifyQuery &Q) {
+/// Return true if V1 == (binop V2, X), where X is known non-zero.
+/// Only handle a small subset of binops where (binop V2, X) with non-zero X
+/// implies V2 != V1.
+static bool isModifyingBinopOfNonZero(const Value *V1, const Value *V2,
+                                      unsigned Depth, const SimplifyQuery &Q) {
   const BinaryOperator *BO = dyn_cast<BinaryOperator>(V1);
-  if (!BO || BO->getOpcode() != Instruction::Add)
+  if (!BO)
     return false;
-  Value *Op = nullptr;
-  if (V2 == BO->getOperand(0))
-    Op = BO->getOperand(1);
-  else if (V2 == BO->getOperand(1))
-    Op = BO->getOperand(0);
-  else
-    return false;
-  return isKnownNonZero(Op, Depth + 1, Q);
+  switch (BO->getOpcode()) {
+  default:
+    break;
+  case Instruction::Or:
+    if (!cast<PossiblyDisjointInst>(V1)->isDisjoint())
+      break;
+    [[fallthrough]];
+  case Instruction::Xor:
+  case Instruction::Add:
+    Value *Op = nullptr;
+    if (V2 == BO->getOperand(0))
+      Op = BO->getOperand(1);
+    else if (V2 == BO->getOperand(1))
+      Op = BO->getOperand(0);
+    else
+      return false;
+    return isKnownNonZero(Op, Depth + 1, Q);
+  }
+  return false;
 }
 
 /// Return true if V2 == V1 * C, where V1 is known non-zero, C is not 0/1 and
@@ -3265,7 +3278,8 @@ static bool isKnownNonEqual(const Value *V1, const Value *V2, unsigned Depth,
     };
   }
 
-  if (isAddOfNonZero(V1, V2, Depth, Q) || isAddOfNonZero(V2, V1, Depth, Q))
+  if (isModifyingBinopOfNonZero(V1, V2, Depth, Q) ||
+      isModifyingBinopOfNonZero(V2, V1, Depth, Q))
     return true;
 
   if (isNonEqualMul(V1, V2, Depth, Q) || isNonEqualMul(V2, V1, Depth, Q))
diff --git a/llvm/test/Transforms/InstSimplify/icmp.ll b/llvm/test/Transforms/InstSimplify/icmp.ll
index 3109768bdfe005..2e6d4a4b981a2e 100644
--- a/llvm/test/Transforms/InstSimplify/icmp.ll
+++ b/llvm/test/Transforms/InstSimplify/icmp.ll
@@ -270,7 +270,7 @@ define i1 @load_ptr(ptr %p) {
 
 define i1 @load_ptr_null_valid(ptr %p) null_pointer_is_valid {
 ; CHECK-LABEL: @load_ptr_null_valid(
-; CHECK-NEXT:    [[LOAD_P:%.*]] = load ptr, ptr [[P:%.*]], align 8, !dereferenceable !0
+; CHECK-NEXT:    [[LOAD_P:%.*]] = load ptr, ptr [[P:%.*]], align 8, !dereferenceable [[META0:![0-9]+]]
 ; CHECK-NEXT:    [[R:%.*]] = icmp ne ptr [[LOAD_P]], null
 ; CHECK-NEXT:    ret i1 [[R]]
 ;
@@ -278,3 +278,62 @@ define i1 @load_ptr_null_valid(ptr %p) null_pointer_is_valid {
   %r = icmp ne ptr %load_p, null
   ret i1 %r
 }
+
+
+define i1 @non_eq_disjoint_or(i8 %x, i8 %yy, i8 %w) {
+; CHECK-LABEL: @non_eq_disjoint_or(
+; CHECK-NEXT:    ret i1 false
+;
+  %y = add nuw i8 %yy, 1
+  %lhs = add i8 %x, %w
+  %val = or disjoint i8 %y, %w
+  %rhs = add i8 %x, %val
+  %r = icmp eq i8 %lhs, %rhs
+  ret i1 %r
+}
+
+define i1 @non_eq_or_fail(i8 %x, i8 %yy, i8 %w) {
+; CHECK-LABEL: @non_eq_or_fail(
+; CHECK-NEXT:    [[Y:%.*]] = add nuw i8 [[YY:%.*]], 1
+; CHECK-NEXT:    [[LHS:%.*]] = add i8 [[X:%.*]], [[W:%.*]]
+; CHECK-NEXT:    [[VAL:%.*]] = or i8 [[Y]], [[W]]
+; CHECK-NEXT:    [[RHS:%.*]] = add i8 [[X]], [[VAL]]
+; CHECK-NEXT:    [[R:%.*]] = icmp eq i8 [[LHS]], [[RHS]]
+; CHECK-NEXT:    ret i1 [[R]]
+;
+  %y = add nuw i8 %yy, 1
+  %lhs = add i8 %x, %w
+  %val = or i8 %y, %w
+  %rhs = add i8 %x, %val
+  %r = icmp eq i8 %lhs, %rhs
+  ret i1 %r
+}
+
+define i1 @non_eq_xor(i8 %x, i8 %yy, i8 %w) {
+; CHECK-LABEL: @non_eq_xor(
+; CHECK-NEXT:    ret i1 false
+;
+  %y = add nuw i8 %yy, 1
+  %lhs = add i8 %x, %w
+  %val = xor i8 %y, %w
+  %rhs = add i8 %x, %val
+  %r = icmp eq i8 %lhs, %rhs
+  ret i1 %r
+}
+
+define i1 @non_eq_xor_fail(i8 %x, i8 %yy, i8 %w) {
+; CHECK-LABEL: @non_eq_xor_fail(
+; CHECK-NEXT:    [[Y:%.*]] = add nsw i8 [[YY:%.*]], 1
+; CHECK-NEXT:    [[LHS:%.*]] = add i8 [[X:%.*]], [[W:%.*]]
+; CHECK-NEXT:    [[VAL:%.*]] = xor i8 [[Y]], [[W]]
+; CHECK-NEXT:    [[RHS:%.*]] = add i8 [[X]], [[VAL]]
+; CHECK-NEXT:    [[R:%.*]] = icmp eq i8 [[LHS]], [[RHS]]
+; CHECK-NEXT:    ret i1 [[R]]
+;
+  %y = add nsw i8 %yy, 1
+  %lhs = add i8 %x, %w
+  %val = xor i8 %y, %w
+  %rhs = add i8 %x, %val
+  %r = icmp eq i8 %lhs, %rhs
+  ret i1 %r
+}

[nikic]

LGTM