ValueTracking: introduce llvm::isNotCrossLaneOperation (llvm#112011)

Factor out and unify common code from InstSimplify and InstCombine that
partially guard against cross-lane vector operations into
llvm::isNotCrossLaneOperation in ValueTracking.

Alive2 proofs for changed tests: https://alive2.llvm.org/ce/z/68H4ka

Author: artagnon

llvm/include/llvm/Analysis/ValueTracking.h

@@ -791,6 +791,9 @@ bool onlyUsedByLifetimeMarkers(const Value *V);
 /// droppable instructions.
 bool onlyUsedByLifetimeMarkersOrDroppableInsts(const Value *V);
 
+/// Return true if the instruction doesn't potentially cross vector lanes.
+bool isNotCrossLaneOperation(const Instruction *I);
+
 /// Return true if the instruction does not have any effects besides
 /// calculating the result and does not have undefined behavior.
 ///

llvm/lib/Analysis/InstructionSimplify.cpp

@@ -4343,13 +4343,10 @@ static Value *simplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
   if (isa<PHINode>(I))
     return nullptr;
 
-  if (Op->getType()->isVectorTy()) {
-    // For vector types, the simplification must hold per-lane, so forbid
-    // potentially cross-lane operations like shufflevector.
-    if (!I->getType()->isVectorTy() || isa<ShuffleVectorInst>(I) ||
-        isa<CallBase>(I) || isa<BitCastInst>(I))
-      return nullptr;
-  }
+  // For vector types, the simplification must hold per-lane, so forbid
+  // potentially cross-lane operations like shufflevector.
+  if (Op->getType()->isVectorTy() && !isNotCrossLaneOperation(I))
+    return nullptr;
 
   // Don't fold away llvm.is.constant checks based on assumptions.
   if (match(I, m_Intrinsic<Intrinsic::is_constant>()))

llvm/lib/Analysis/ValueTracking.cpp

@@ -6947,6 +6947,29 @@ bool llvm::onlyUsedByLifetimeMarkersOrDroppableInsts(const Value *V) {
       V, /* AllowLifetime */ true, /* AllowDroppable */ true);
 }
 
+bool llvm::isNotCrossLaneOperation(const Instruction *I) {
+  if (auto *II = dyn_cast<IntrinsicInst>(I)) {
+    switch (II->getIntrinsicID()) {
+    // TODO: expand this list.
+    case Intrinsic::ctlz:
+    case Intrinsic::cttz:
+    case Intrinsic::ctpop:
+    case Intrinsic::umin:
+    case Intrinsic::umax:
+    case Intrinsic::smin:
+    case Intrinsic::smax:
+    case Intrinsic::usub_sat:
+    case Intrinsic::uadd_sat:
+    case Intrinsic::ssub_sat:
+    case Intrinsic::sadd_sat:
+      return true;
+    default:
+      return false;
+    }
+  }
+  return !isa<CallBase, BitCastInst, ShuffleVectorInst, ExtractElementInst>(I);
+}
+
 bool llvm::isSafeToSpeculativelyExecute(const Instruction *Inst,
                                         const Instruction *CtxI,
                                         AssumptionCache *AC,

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -3636,26 +3636,12 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
   //  * The intrinsic is speculatable.
   //  * The select condition is not a vector, or the intrinsic does not
   //    perform cross-lane operations.
-  switch (IID) {
-  case Intrinsic::ctlz:
-  case Intrinsic::cttz:
-  case Intrinsic::ctpop:
-  case Intrinsic::umin:
-  case Intrinsic::umax:
-  case Intrinsic::smin:
-  case Intrinsic::smax:
-  case Intrinsic::usub_sat:
-  case Intrinsic::uadd_sat:
-  case Intrinsic::ssub_sat:
-  case Intrinsic::sadd_sat:
+  if (isSafeToSpeculativelyExecuteWithVariableReplaced(&CI) &&
+      isNotCrossLaneOperation(II))
     for (Value *Op : II->args())
       if (auto *Sel = dyn_cast<SelectInst>(Op))
         if (Instruction *R = FoldOpIntoSelect(*II, Sel))
           return R;
-    [[fallthrough]];
-  default:
-    break;
-  }
 
   if (Instruction *Shuf = foldShuffledIntrinsicOperands(II, Builder))
     return Shuf;

llvm/test/Transforms/InstCombine/ispow2.ll

@@ -977,11 +977,7 @@ define i1 @is_pow2or0_ctpop_wrong_pred2_logical(i32 %x) {
 
 define <2 x i1> @is_pow2or0_ctpop_commute_vec_wrong_pred3(<2 x i8> %x) {
 ; CHECK-LABEL: @is_pow2or0_ctpop_commute_vec_wrong_pred3(
-; CHECK-NEXT:    [[T0:%.*]] = tail call range(i8 0, 9) <2 x i8> @llvm.ctpop.v2i8(<2 x i8> [[X:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq <2 x i8> [[T0]], <i8 1, i8 1>
-; CHECK-NEXT:    [[ISZERO:%.*]] = icmp eq <2 x i8> [[X]], zeroinitializer
-; CHECK-NEXT:    [[R:%.*]] = and <2 x i1> [[CMP]], [[ISZERO]]
-; CHECK-NEXT:    ret <2 x i1> [[R]]
+; CHECK-NEXT:    ret <2 x i1> zeroinitializer
 ;
   %t0 = tail call <2 x i8> @llvm.ctpop.v2i8(<2 x i8> %x)
   %cmp = icmp eq <2 x i8> %t0, <i8 1, i8 1>
@@ -1174,11 +1170,7 @@ define i1 @isnot_pow2nor0_ctpop_wrong_pred2_logical(i32 %x) {
 
 define <2 x i1> @isnot_pow2nor0_wrong_pred3_ctpop_commute_vec(<2 x i8> %x) {
 ; CHECK-LABEL: @isnot_pow2nor0_wrong_pred3_ctpop_commute_vec(
-; CHECK-NEXT:    [[T0:%.*]] = tail call range(i8 0, 9) <2 x i8> @llvm.ctpop.v2i8(<2 x i8> [[X:%.*]])
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ne <2 x i8> [[T0]], <i8 1, i8 1>
-; CHECK-NEXT:    [[NOTZERO:%.*]] = icmp ne <2 x i8> [[X]], zeroinitializer
-; CHECK-NEXT:    [[R:%.*]] = or <2 x i1> [[CMP]], [[NOTZERO]]
-; CHECK-NEXT:    ret <2 x i1> [[R]]
+; CHECK-NEXT:    ret <2 x i1> <i1 true, i1 true>
 ;
   %t0 = tail call <2 x i8> @llvm.ctpop.v2i8(<2 x i8> %x)
   %cmp = icmp ne <2 x i8> %t0, <i8 1, i8 1>

llvm/test/Transforms/InstCombine/select-ctlz-to-cttz.ll

@@ -208,10 +208,8 @@ define <2 x i32> @select_clz_to_ctz_vec_with_undef(<2 x i32> %a) {
 ; CHECK-NEXT:    [[SUB:%.*]] = sub <2 x i32> zeroinitializer, [[A:%.*]]
 ; CHECK-NEXT:    [[AND:%.*]] = and <2 x i32> [[A]], [[SUB]]
 ; CHECK-NEXT:    [[LZ:%.*]] = tail call range(i32 0, 33) <2 x i32> @llvm.ctlz.v2i32(<2 x i32> [[AND]], i1 true)
-; CHECK-NEXT:    [[TOBOOL:%.*]] = icmp eq <2 x i32> [[A]], zeroinitializer
 ; CHECK-NEXT:    [[SUB1:%.*]] = xor <2 x i32> [[LZ]], <i32 31, i32 undef>
-; CHECK-NEXT:    [[COND:%.*]] = select <2 x i1> [[TOBOOL]], <2 x i32> [[LZ]], <2 x i32> [[SUB1]]
-; CHECK-NEXT:    ret <2 x i32> [[COND]]
+; CHECK-NEXT:    ret <2 x i32> [[SUB1]]
 ;
   %sub = sub <2 x i32> zeroinitializer, %a
   %and = and <2 x i32> %sub, %a

llvm/test/Transforms/InstSimplify/select.ll

@@ -1087,13 +1087,10 @@ define i32 @select_ctpop_zero(i32 %x) {
   ret i32 %sel
 }
 
-; FIXME: This is safe to fold.
 define <2 x i32> @select_ctpop_zero_vec(<2 x i32> %x) {
 ; CHECK-LABEL: @select_ctpop_zero_vec(
-; CHECK-NEXT:    [[T0:%.*]] = icmp eq <2 x i32> [[X:%.*]], zeroinitializer
-; CHECK-NEXT:    [[T1:%.*]] = call <2 x i32> @llvm.ctpop.v2i32(<2 x i32> [[X]])
-; CHECK-NEXT:    [[SEL:%.*]] = select <2 x i1> [[T0]], <2 x i32> zeroinitializer, <2 x i32> [[T1]]
-; CHECK-NEXT:    ret <2 x i32> [[SEL]]
+; CHECK-NEXT:    [[T1:%.*]] = call <2 x i32> @llvm.ctpop.v2i32(<2 x i32> [[X:%.*]])
+; CHECK-NEXT:    ret <2 x i32> [[T1]]
 ;
   %t0 = icmp eq <2 x i32> %x, zeroinitializer
   %t1 = call <2 x i32> @llvm.ctpop.v2i32(<2 x i32> %x)