[InstCombine] Fold ceil(X / (2 ^ C)) == 0 -> X == 0

llvm/include/llvm/Analysis/ValueTracking.h

@@ -999,6 +999,11 @@ LLVM_ABI void
 findValuesAffectedByCondition(Value *Cond, bool IsAssume,
                               function_ref<void(Value *)> InsertAffected);
 
+/// Returns the inner value X if the expression has the form f(X)
+/// where f(X) == 0 if and only if X == 0, otherwise returns nullptr.
+LLVM_ABI Value *stripNullTest(Value *V);
+LLVM_ABI const Value *stripNullTest(const Value *V);
+
 } // end namespace llvm
 
 #endif // LLVM_ANALYSIS_VALUETRACKING_H

llvm/lib/Analysis/ValueTracking.cpp

@@ -3521,6 +3521,9 @@ bool isKnownNonZero(const Value *V, const APInt &DemandedElts,
       isKnownNonNullFromDominatingCondition(V, Q.CxtI, Q.DT))
     return true;
 
+  if (const Value *Stripped = stripNullTest(V))
+    return isKnownNonZero(Stripped, DemandedElts, Q, Depth);
+
   return false;
 }
 
@@ -10170,3 +10173,26 @@ void llvm::findValuesAffectedByCondition(
     }
   }
 }
+
+const Value *llvm::stripNullTest(const Value *V) {
+  // (X >> C) or/add (X & mask(C) != 0)
+  if (const auto *BO = dyn_cast<BinaryOperator>(V)) {
+    if (BO->getOpcode() == Instruction::Add ||
+        BO->getOpcode() == Instruction::Or) {
+      const Value *X;
+      const APInt *C1, *C2;
+      if (match(BO, m_c_BinOp(m_LShr(m_Value(X), m_APInt(C1)),
+                              m_ZExt(m_SpecificICmp(
+                                  ICmpInst::ICMP_NE,
+                                  m_And(m_Deferred(X), m_LowBitMask(C2)),
+                                  m_Zero())))) &&
+          C2->popcount() == C1->getZExtValue())
+        return X;
+    }
+  }
+  return nullptr;
+}
+
+Value *llvm::stripNullTest(Value *V) {
+  return const_cast<Value *>(stripNullTest(const_cast<const Value *>(V)));
+}

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -1298,6 +1298,13 @@ Instruction *InstCombinerImpl::foldICmpWithZero(ICmpInst &Cmp) {
     // eq/ne (mul X, Y)) with (icmp eq/ne X/Y) and if X/Y is known non-zero that
     // will fold to a constant elsewhere.
   }
+
+  // (icmp eq/ne f(X), 0) -> (icmp eq/ne X, 0)
+  // where f(X) == 0 if and only if X == 0
+  if (ICmpInst::isEquality(Pred))
+    if (Value *Stripped = stripNullTest(Cmp.getOperand(0)))
+      return new ICmpInst(Pred, Stripped, Cmp.getOperand(1));
+
   return nullptr;
 }
 

llvm/test/Transforms/InstCombine/ceil-shift.ll

@@ -0,0 +1,308 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+define i1 @ceil_shift4(i32 %arg0) {
+; CHECK-LABEL: define i1 @ceil_shift4(
+; CHECK-SAME: i32 [[ARG0:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i32 [[ARG0]], 0
+; CHECK-NEXT:    ret i1 [[TMP1]]
+;
+  %quot = lshr i32 %arg0, 4
+  %rem = and i32 %arg0, 15
+  %has_rem = icmp ne i32 %rem, 0
+  %zext_has_rem = zext i1 %has_rem to i32
+  %quot_or_rem = or i32 %quot, %zext_has_rem
+  %is_zero = icmp eq i32 %quot_or_rem, 0
+  ret i1 %is_zero
+}
+
+define i1 @ceil_shift4_add(i32 %arg0) {
+; CHECK-LABEL: define i1 @ceil_shift4_add(
+; CHECK-SAME: i32 [[ARG0:%.*]]) {
+; CHECK-NEXT:    [[TMP6:%.*]] = icmp eq i32 [[ARG0]], 0
+; CHECK-NEXT:    ret i1 [[TMP6]]
+;
+  %quot = lshr i32 %arg0, 4
+  %rem = and i32 %arg0, 15
+  %has_rem = icmp ne i32 %rem, 0
+  %zext_has_rem = zext i1 %has_rem to i32
+  %ceil = add i32 %quot, %zext_has_rem
+  %res = icmp eq i32 %ceil, 0
+  ret i1 %res
+}
+
+define i1 @ceil_shift6(i32 %arg0) {
+; CHECK-LABEL: define i1 @ceil_shift6(
+; CHECK-SAME: i32 [[ARG0:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i32 [[ARG0]], 0
+; CHECK-NEXT:    ret i1 [[TMP1]]
+;
+  %quot = lshr i32 %arg0, 6
+  %rem = and i32 %arg0, 63
+  %has_rem = icmp ne i32 %rem, 0
+  %zext_has_rem = zext i1 %has_rem to i32
+  %quot_or_rem = or i32 %quot, %zext_has_rem
+  %res = icmp eq i32 %quot_or_rem, 0
+  ret i1 %res
+}
+
+define i1 @ceil_shift6_ne(i32 %arg0) {
+; CHECK-LABEL: define i1 @ceil_shift6_ne(
+; CHECK-SAME: i32 [[ARG0:%.*]]) {
+; CHECK-NEXT:    [[RES:%.*]] = icmp ne i32 [[ARG0]], 0
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %quot = lshr i32 %arg0, 6
+  %rem = and i32 %arg0, 63
+  %has_rem = icmp ne i32 %rem, 0
+  %zext_has_rem = zext i1 %has_rem to i32
+  %quot_or_rem = or i32 %quot, %zext_has_rem
+  %res = icmp ne i32 %quot_or_rem, 0
+  ret i1 %res
+}
+
+define i1 @ceil_shift11(i32 %arg0) {
+; CHECK-LABEL: define i1 @ceil_shift11(
+; CHECK-SAME: i32 [[ARG0:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i32 [[ARG0]], 0
+; CHECK-NEXT:    ret i1 [[TMP1]]
+;
+  %quot = lshr i32 %arg0, 11
+  %rem = and i32 %arg0, 2047
+  %has_rem = icmp ne i32 %rem, 0
+  %zext_has_rem = zext i1 %has_rem to i32
+  %quot_or_rem = or i32 %quot, %zext_has_rem
+  %res = icmp eq i32 %quot_or_rem, 0
+  ret i1 %res
+}
+
+define i1 @ceil_shift11_ne(i32 %arg0) {
+; CHECK-LABEL: define i1 @ceil_shift11_ne(
+; CHECK-SAME: i32 [[ARG0:%.*]]) {
+; CHECK-NEXT:    [[RES:%.*]] = icmp ne i32 [[ARG0]], 0
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %quot = lshr i32 %arg0, 6
+  %rem = and i32 %arg0, 63
+  %has_rem = icmp ne i32 %rem, 0
+  %zext_has_rem = zext i1 %has_rem to i32
+  %quot_or_rem = or i32 %quot, %zext_has_rem
+  %res = icmp ne i32 %quot_or_rem, 0
+  ret i1 %res
+}
+
+define i1 @ceil_shift0(i32 %arg0) {
+; CHECK-LABEL: define i1 @ceil_shift0(
+; CHECK-SAME: i32 [[ARG0:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq i32 [[ARG0]], 0
+; CHECK-NEXT:    ret i1 [[TMP1]]
+;
+  %quot = lshr i32 %arg0, 0
+  %rem = and i32 %arg0, 0
+  %has_rem = icmp ne i32 %rem, 0
+  %zext_has_rem = zext i1 %has_rem to i32
+  %quot_or_rem = or i32 %quot, %zext_has_rem
+  %res = icmp eq i32 %quot_or_rem, 0
+  ret i1 %res
+}
+
+define i1 @ceil_shift4_comm(i32 %arg0) {
+; CHECK-LABEL: define i1 @ceil_shift4_comm(
+; CHECK-SAME: i32 [[ARG0:%.*]]) {
+; CHECK-NEXT:    [[TMP6:%.*]] = icmp eq i32 [[ARG0]], 0
+; CHECK-NEXT:    ret i1 [[TMP6]]
+;
+  %quot = lshr i32 %arg0, 4
+  %rem = and i32 %arg0, 15
+  %has_rem = icmp ne i32 %rem, 0
+  %zext_has_rem = zext i1 %has_rem to i32
+  %quot_or_rem = or i32 %zext_has_rem, %quot
+  %res = icmp eq i32 %quot_or_rem, 0
+  ret i1 %res
+}
+
+declare void @use(i32)
+
+define i1 @ceil_shift4_used_1(i32 %arg0) {
+; CHECK-LABEL: define i1 @ceil_shift4_used_1(
+; CHECK-SAME: i32 [[ARG0:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = lshr i32 [[ARG0]], 4
+; CHECK-NEXT:    call void @use(i32 [[TMP1]])
+; CHECK-NEXT:    [[TMP6:%.*]] = icmp eq i32 [[ARG0]], 0
+; CHECK-NEXT:    ret i1 [[TMP6]]
+;
+  %quot = lshr i32 %arg0, 4
+  call void @use(i32 %quot)
+  %rem = and i32 %arg0, 15
+  %has_rem = icmp ne i32 %rem, 0
+  %zext_has_rem = zext i1 %has_rem to i32
+  %quot_or_rem = or i32 %quot, %zext_has_rem
+  %res = icmp eq i32 %quot_or_rem, 0
+  ret i1 %res
+}
+
+define i1 @ceil_shift4_used_5(i32 %arg0) {
+; CHECK-LABEL: define i1 @ceil_shift4_used_5(
+; CHECK-SAME: i32 [[ARG0:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = lshr i32 [[ARG0]], 4
+; CHECK-NEXT:    [[TMP2:%.*]] = and i32 [[ARG0]], 15
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp ne i32 [[TMP2]], 0
+; CHECK-NEXT:    [[TMP4:%.*]] = zext i1 [[TMP3]] to i32
+; CHECK-NEXT:    [[TMP5:%.*]] = or i32 [[TMP1]], [[TMP4]]
+; CHECK-NEXT:    call void @use(i32 [[TMP5]])
+; CHECK-NEXT:    [[TMP6:%.*]] = icmp eq i32 [[ARG0]], 0
+; CHECK-NEXT:    ret i1 [[TMP6]]
+;
+  %quot = lshr i32 %arg0, 4
+  %rem = and i32 %arg0, 15
+  %has_rem = icmp ne i32 %rem, 0
+  %zext_has_rem = zext i1 %has_rem to i32
+  %quot_or_rem = or i32 %quot, %zext_has_rem
+  call void @use(i32 %quot_or_rem)
+  %res = icmp eq i32 %quot_or_rem, 0
+  ret i1 %res
+}
+
+define i1 @ceil_shift4_used_add_nuw_nsw(i32 %arg0) {
+; CHECK-LABEL: define i1 @ceil_shift4_used_add_nuw_nsw(
+; CHECK-SAME: i32 [[ARG0:%.*]]) {
+; CHECK-NEXT:    [[QUOT:%.*]] = lshr i32 [[ARG0]], 4
+; CHECK-NEXT:    [[REM:%.*]] = and i32 [[ARG0]], 15
+; CHECK-NEXT:    [[HAS_REM:%.*]] = icmp ne i32 [[REM]], 0
+; CHECK-NEXT:    [[ZEXT_HAS_REM:%.*]] = zext i1 [[HAS_REM]] to i32
+; CHECK-NEXT:    [[CEIL:%.*]] = add nuw nsw i32 [[QUOT]], [[ZEXT_HAS_REM]]
+; CHECK-NEXT:    call void @use(i32 [[CEIL]])
+; CHECK-NEXT:    [[RES:%.*]] = icmp eq i32 [[ARG0]], 0
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %quot = lshr i32 %arg0, 4
+  %rem = and i32 %arg0, 15
+  %has_rem = icmp ne i32 %rem, 0
+  %zext_has_rem = zext i1 %has_rem to i32
+  %ceil = add nuw nsw i32 %quot, %zext_has_rem
+  call void @use(i32 %ceil)
+  %res = icmp eq i32 %ceil, 0
+  ret i1 %res
+}
+
+define <4 x i1> @ceil_shift4_v4i32(<4 x i32> %arg0) {
+; CHECK-LABEL: define <4 x i1> @ceil_shift4_v4i32(
+; CHECK-SAME: <4 x i32> [[ARG0:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq <4 x i32> [[ARG0]], zeroinitializer
+; CHECK-NEXT:    ret <4 x i1> [[TMP1]]
+;
+  %quot = lshr <4 x i32> %arg0, splat (i32 16)
+  %rem = and <4 x i32> %arg0, splat (i32 65535)
+  %has_rem = icmp ne <4 x i32> %rem, zeroinitializer
+  %zext_has_rem = zext <4 x i1> %has_rem to <4 x i32>
+  %quot_or_rem = or <4 x i32> %quot, %zext_has_rem
+  %res = icmp eq <4 x i32> %quot_or_rem, zeroinitializer
+  ret <4 x i1> %res
+}
+
+define <8 x i1> @ceil_shift4_v8i16(<8 x i16> %arg0) {
+; CHECK-LABEL: define <8 x i1> @ceil_shift4_v8i16(
+; CHECK-SAME: <8 x i16> [[ARG0:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp eq <8 x i16> [[ARG0]], zeroinitializer
+; CHECK-NEXT:    ret <8 x i1> [[TMP1]]
+;
+  %quot = lshr <8 x i16> %arg0, splat (i16 4)
+  %rem = and <8 x i16> %arg0, splat (i16 15)
+  %has_rem = icmp ne <8 x i16> %rem, zeroinitializer
+  %zext_has_rem = zext <8 x i1> %has_rem to <8 x i16>
+  %quot_or_rem = or <8 x i16> %quot, %zext_has_rem
+  %res = icmp eq <8 x i16> %quot_or_rem, zeroinitializer
+  ret <8 x i1> %res
+}
+
+; negative tests
+
+define i1 @ceil_shift_not_mask_1(i32 %arg0) {
+; CHECK-LABEL: define i1 @ceil_shift_not_mask_1(
+; CHECK-SAME: i32 [[ARG0:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = lshr i32 [[ARG0]], 4
+; CHECK-NEXT:    [[TMP2:%.*]] = and i32 [[ARG0]], 31
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp ne i32 [[TMP2]], 0
+; CHECK-NEXT:    [[TMP4:%.*]] = zext i1 [[TMP3]] to i32
+; CHECK-NEXT:    [[TMP5:%.*]] = or i32 [[TMP1]], [[TMP4]]
+; CHECK-NEXT:    [[TMP6:%.*]] = icmp eq i32 [[TMP5]], 0
+; CHECK-NEXT:    ret i1 [[TMP6]]
+;
+  %quot = lshr i32 %arg0, 4
+  %rem = and i32 %arg0, 31
+  %has_rem = icmp ne i32 %rem, 0
+  %zext_has_rem = zext i1 %has_rem to i32
+  %quot_or_rem = or i32 %quot, %zext_has_rem
+  %res = icmp eq i32 %quot_or_rem, 0
+  ret i1 %res
+}
+
+define i1 @ceil_shift_not_mask_2(i32 %arg0) {
+; CHECK-LABEL: define i1 @ceil_shift_not_mask_2(
+; CHECK-SAME: i32 [[ARG0:%.*]]) {
+; CHECK-NEXT:    [[TMP1:%.*]] = lshr i32 [[ARG0]], 5
+; CHECK-NEXT:    [[TMP2:%.*]] = and i32 [[ARG0]], 15
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp ne i32 [[TMP2]], 0
+; CHECK-NEXT:    [[TMP4:%.*]] = zext i1 [[TMP3]] to i32
+; CHECK-NEXT:    [[TMP5:%.*]] = or i32 [[TMP1]], [[TMP4]]
+; CHECK-NEXT:    [[TMP6:%.*]] = icmp eq i32 [[TMP5]], 0
+; CHECK-NEXT:    ret i1 [[TMP6]]
+;
+  %quot = lshr i32 %arg0, 5
+  %rem = and i32 %arg0, 15
+  %has_rem = icmp ne i32 %rem, 0
+  %zext_has_rem = zext i1 %has_rem to i32
+  %quot_or_rem = or i32 %quot, %zext_has_rem
+  %res = icmp eq i32 %quot_or_rem, 0
+  ret i1 %res
+}
+
+define i1 @ceil_shift_not_add_or(i32 %arg0) {
+; CHECK-LABEL: define i1 @ceil_shift_not_add_or(
+; CHECK-SAME: i32 [[ARG0:%.*]]) {
+; CHECK-NEXT:    [[REM:%.*]] = and i32 [[ARG0]], 15
+; CHECK-NEXT:    [[HAS_REM_NOT:%.*]] = icmp eq i32 [[REM]], 0
+; CHECK-NEXT:    [[TMP1:%.*]] = and i32 [[ARG0]], 32
+; CHECK-NEXT:    [[RES1:%.*]] = icmp eq i32 [[TMP1]], 0
+; CHECK-NEXT:    [[RES:%.*]] = or i1 [[HAS_REM_NOT]], [[RES1]]
+; CHECK-NEXT:    ret i1 [[RES]]
+;
+  %quot = lshr i32 %arg0, 5
+  %rem = and i32 %arg0, 15
+  %has_rem = icmp ne i32 %rem, 0
+  %zext_has_rem = zext i1 %has_rem to i32
+  %quot_and_rem = and i32 %quot, %zext_has_rem
+  %res = icmp eq i32 %quot_and_rem, 0
+  ret i1 %res
+}
+
+define i32 @ceil_shift_should_infer_ge_zero(i32 %x) {
+; CHECK-LABEL: define i32 @ceil_shift_should_infer_ge_zero(
+; CHECK-SAME: i32 [[X:%.*]]) {
+; CHECK-NEXT:    [[COND_NOT:%.*]] = icmp eq i32 [[X]], 0
+; CHECK-NEXT:    br i1 [[COND_NOT]], label %[[IF_ELSE:.*]], label %[[IF_THEN:.*]]
+; CHECK:       [[IF_THEN]]:
+; CHECK-NEXT:    [[TMP1:%.*]] = lshr i32 [[X]], 20
+; CHECK-NEXT:    [[TMP2:%.*]] = and i32 [[X]], 1048575
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp ne i32 [[TMP2]], 0
+; CHECK-NEXT:    [[TMP4:%.*]] = zext i1 [[TMP3]] to i32
+; CHECK-NEXT:    [[TMP5:%.*]] = add nuw nsw i32 [[TMP1]], [[TMP4]]
+; CHECK-NEXT:    ret i32 [[TMP5]]
+; CHECK:       [[IF_ELSE]]:
+; CHECK-NEXT:    ret i32 0
+;
+  %cond = icmp ne i32 %x, 0
+  br i1 %cond, label %if.then, label %if.else
+
+if.then:
+  %quot = lshr i32 %x, 20
+  %rem = and i32 %x, 1048575
+  %has_rem = icmp ne i32 %rem, 0
+  %zext_has_rem = zext i1 %has_rem to i32
+  %ceil = add nuw nsw i32 %quot, %zext_has_rem
+  %max = call i32 @llvm.umax.i32(i32 %ceil, i32 1)
+  ret i32 %max
+
+if.else:
+  ret i32 0
+}