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merged 3 commits into from
Sep 20, 2025
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[ValueTracking] a - b == NonZero -> a != b #159792

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45d0824
[ValueTracking] Add pre-commit tests. NFC.
dtcxzyw Sep 19, 2025
e2bbe01
[ValueTracking] a - b == NonZero -> a != b
dtcxzyw Sep 19, 2025
eb18e43
[ValueTracking] Rename RHSC to L1C. NFC.
dtcxzyw Sep 20, 2025
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22 changes: 21 additions & 1 deletion llvm/lib/Analysis/ValueTracking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -9425,6 +9425,21 @@ isImpliedCondICmps(CmpPredicate LPred, const Value *L0, const Value *L1,
return true;
}

// a - b == NonZero -> a != b
// ptrtoint(a) - ptrtoint(b) == NonZero -> a != b
const APInt *L1C;
Value *A, *B;
if (LPred == ICmpInst::ICMP_EQ && ICmpInst::isEquality(RPred) &&
match(L1, m_APInt(L1C)) && !L1C->isZero() &&
match(L0, m_Sub(m_Value(A), m_Value(B))) &&
((A == R0 && B == R1) || (A == R1 && B == R0) ||
(match(A, m_PtrToInt(m_Specific(R0))) &&
match(B, m_PtrToInt(m_Specific(R1)))) ||
(match(A, m_PtrToInt(m_Specific(R1))) &&
match(B, m_PtrToInt(m_Specific(R0)))))) {
return RPred.dropSameSign() == ICmpInst::ICMP_NE;
}

// L0 = R0 = L1 + R1, L0 >=u L1 implies R0 >=u R1, L0 <u L1 implies R0 <u R1
if (L0 == R0 &&
(LPred == ICmpInst::ICMP_ULT || LPred == ICmpInst::ICMP_UGE) &&
Expand Down Expand Up @@ -10180,15 +10195,20 @@ void llvm::findValuesAffectedByCondition(
AddAffected(B);
if (HasRHSC) {
Value *Y;
// (X & C) or (X | C).
// (X << C) or (X >>_s C) or (X >>_u C).
if (match(A, m_Shift(m_Value(X), m_ConstantInt())))
AddAffected(X);
// (X & C) or (X | C).
else if (match(A, m_And(m_Value(X), m_Value(Y))) ||
match(A, m_Or(m_Value(X), m_Value(Y)))) {
AddAffected(X);
AddAffected(Y);
}
// X - Y
else if (match(A, m_Sub(m_Value(X), m_Value(Y)))) {
AddAffected(X);
AddAffected(Y);
}
}
} else {
AddCmpOperands(A, B);
Expand Down
186 changes: 186 additions & 0 deletions llvm/test/Transforms/InstCombine/icmp.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -6054,3 +6054,189 @@ define i1 @icmp_samesign_logical_or(i32 %In) {
%V = select i1 %c1, i1 true, i1 %c2
ret i1 %V
}

define i1 @non_zero_ptrdiff_implies_icmp_eq(ptr %p0, ptr %p1) {
; CHECK-LABEL: define i1 @non_zero_ptrdiff_implies_icmp_eq(
; CHECK-SAME: ptr [[P0:%.*]], ptr [[P1:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[I0:%.*]] = ptrtoint ptr [[P0]] to i64
; CHECK-NEXT: [[I1:%.*]] = ptrtoint ptr [[P1]] to i64
; CHECK-NEXT: [[DIFF:%.*]] = sub i64 [[I0]], [[I1]]
; CHECK-NEXT: [[COND:%.*]] = icmp eq i64 [[DIFF]], 12
; CHECK-NEXT: call void @llvm.assume(i1 [[COND]])
; CHECK-NEXT: ret i1 false
;
entry:
%i0 = ptrtoint ptr %p0 to i64
%i1 = ptrtoint ptr %p1 to i64
%diff = sub i64 %i0, %i1
%cond = icmp eq i64 %diff, 12
call void @llvm.assume(i1 %cond)
%cmp = icmp eq ptr %p0, %p1
ret i1 %cmp
}

define i1 @non_zero_ptrdiff_implies_icmp_eq_commuted(ptr %p0, ptr %p1) {
; CHECK-LABEL: define i1 @non_zero_ptrdiff_implies_icmp_eq_commuted(
; CHECK-SAME: ptr [[P0:%.*]], ptr [[P1:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[I0:%.*]] = ptrtoint ptr [[P0]] to i64
; CHECK-NEXT: [[I1:%.*]] = ptrtoint ptr [[P1]] to i64
; CHECK-NEXT: [[DIFF:%.*]] = sub i64 [[I0]], [[I1]]
; CHECK-NEXT: [[COND:%.*]] = icmp eq i64 [[DIFF]], 12
; CHECK-NEXT: call void @llvm.assume(i1 [[COND]])
; CHECK-NEXT: ret i1 false
;
entry:
%i0 = ptrtoint ptr %p0 to i64
%i1 = ptrtoint ptr %p1 to i64
%diff = sub i64 %i0, %i1
%cond = icmp eq i64 %diff, 12
call void @llvm.assume(i1 %cond)
%cmp = icmp eq ptr %p1, %p0
ret i1 %cmp
}

define i1 @non_zero_ptrdiff_implies_icmp_ne(ptr %p0, ptr %p1) {
; CHECK-LABEL: define i1 @non_zero_ptrdiff_implies_icmp_ne(
; CHECK-SAME: ptr [[P0:%.*]], ptr [[P1:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[I0:%.*]] = ptrtoint ptr [[P0]] to i64
; CHECK-NEXT: [[I1:%.*]] = ptrtoint ptr [[P1]] to i64
; CHECK-NEXT: [[DIFF:%.*]] = sub i64 [[I0]], [[I1]]
; CHECK-NEXT: [[COND:%.*]] = icmp eq i64 [[DIFF]], 12
; CHECK-NEXT: call void @llvm.assume(i1 [[COND]])
; CHECK-NEXT: ret i1 true
;
entry:
%i0 = ptrtoint ptr %p0 to i64
%i1 = ptrtoint ptr %p1 to i64
%diff = sub i64 %i0, %i1
%cond = icmp eq i64 %diff, 12
call void @llvm.assume(i1 %cond)
%cmp = icmp ne ptr %p0, %p1
ret i1 %cmp
}

; TODO: Handle this case if it is shown in real code.
define i1 @non_zero_truncated_ptrdiff_implies_icmp_ne(ptr %p0, ptr %p1) {
; CHECK-LABEL: define i1 @non_zero_truncated_ptrdiff_implies_icmp_ne(
; CHECK-SAME: ptr [[P0:%.*]], ptr [[P1:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[TMP0:%.*]] = ptrtoint ptr [[P0]] to i64
; CHECK-NEXT: [[I0:%.*]] = trunc i64 [[TMP0]] to i8
; CHECK-NEXT: [[TMP1:%.*]] = ptrtoint ptr [[P1]] to i64
; CHECK-NEXT: [[I1:%.*]] = trunc i64 [[TMP1]] to i8
; CHECK-NEXT: [[DIFF:%.*]] = sub i8 [[I0]], [[I1]]
; CHECK-NEXT: [[COND:%.*]] = icmp eq i8 [[DIFF]], 12
; CHECK-NEXT: call void @llvm.assume(i1 [[COND]])
; CHECK-NEXT: [[CMP:%.*]] = icmp ne ptr [[P0]], [[P1]]
; CHECK-NEXT: ret i1 [[CMP]]
;
entry:
%i0 = ptrtoint ptr %p0 to i8
%i1 = ptrtoint ptr %p1 to i8
%diff = sub i8 %i0, %i1
%cond = icmp eq i8 %diff, 12
call void @llvm.assume(i1 %cond)
%cmp = icmp ne ptr %p0, %p1
ret i1 %cmp
}

define i1 @non_zero_diff_implies_icmp_eq(i8 %p0, i8 %p1) {
; CHECK-LABEL: define i1 @non_zero_diff_implies_icmp_eq(
; CHECK-SAME: i8 [[P0:%.*]], i8 [[P1:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[DIFF:%.*]] = sub i8 [[P0]], [[P1]]
; CHECK-NEXT: [[COND:%.*]] = icmp eq i8 [[DIFF]], 12
; CHECK-NEXT: call void @llvm.assume(i1 [[COND]])
; CHECK-NEXT: ret i1 false
;
entry:
%diff = sub i8 %p0, %p1
%cond = icmp eq i8 %diff, 12
call void @llvm.assume(i1 %cond)
%cmp = icmp eq i8 %p0, %p1
ret i1 %cmp
}

define i1 @non_zero_diff_implies_icmp_eq_commuted(i8 %p0, i8 %p1) {
; CHECK-LABEL: define i1 @non_zero_diff_implies_icmp_eq_commuted(
; CHECK-SAME: i8 [[P0:%.*]], i8 [[P1:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[DIFF:%.*]] = sub i8 [[P0]], [[P1]]
; CHECK-NEXT: [[COND:%.*]] = icmp eq i8 [[DIFF]], 12
; CHECK-NEXT: call void @llvm.assume(i1 [[COND]])
; CHECK-NEXT: ret i1 false
;
entry:
%diff = sub i8 %p0, %p1
%cond = icmp eq i8 %diff, 12
call void @llvm.assume(i1 %cond)
%cmp = icmp eq i8 %p1, %p0
ret i1 %cmp
}

; Negative tests

define i1 @unknown_ptrdiff_implies_icmp_eq1(ptr %p0, ptr %p1) {
; CHECK-LABEL: define i1 @unknown_ptrdiff_implies_icmp_eq1(
; CHECK-SAME: ptr [[P0:%.*]], ptr [[P1:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[I0:%.*]] = ptrtoint ptr [[P0]] to i64
; CHECK-NEXT: [[I1:%.*]] = ptrtoint ptr [[P1]] to i64
; CHECK-NEXT: [[DIFF:%.*]] = sub i64 [[I0]], [[I1]]
; CHECK-NEXT: [[COND:%.*]] = icmp ne i64 [[DIFF]], 12
; CHECK-NEXT: call void @llvm.assume(i1 [[COND]])
; CHECK-NEXT: [[CMP:%.*]] = icmp eq ptr [[P0]], [[P1]]
; CHECK-NEXT: ret i1 [[CMP]]
;
entry:
%i0 = ptrtoint ptr %p0 to i64
%i1 = ptrtoint ptr %p1 to i64
%diff = sub i64 %i0, %i1
%cond = icmp ne i64 %diff, 12
call void @llvm.assume(i1 %cond)
%cmp = icmp eq ptr %p0, %p1
ret i1 %cmp
}

define i1 @unknown_ptrdiff_implies_icmp_eq2(ptr %p0, ptr %p1, i64 %x) {
; CHECK-LABEL: define i1 @unknown_ptrdiff_implies_icmp_eq2(
; CHECK-SAME: ptr [[P0:%.*]], ptr [[P1:%.*]], i64 [[X:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[I0:%.*]] = ptrtoint ptr [[P0]] to i64
; CHECK-NEXT: [[I1:%.*]] = ptrtoint ptr [[P1]] to i64
; CHECK-NEXT: [[DIFF:%.*]] = sub i64 [[I0]], [[I1]]
; CHECK-NEXT: [[COND:%.*]] = icmp eq i64 [[DIFF]], [[X]]
; CHECK-NEXT: call void @llvm.assume(i1 [[COND]])
; CHECK-NEXT: [[CMP:%.*]] = icmp eq ptr [[P0]], [[P1]]
; CHECK-NEXT: ret i1 [[CMP]]
;
entry:
%i0 = ptrtoint ptr %p0 to i64
%i1 = ptrtoint ptr %p1 to i64
%diff = sub i64 %i0, %i1
%cond = icmp eq i64 %diff, %x
call void @llvm.assume(i1 %cond)
%cmp = icmp eq ptr %p0, %p1
ret i1 %cmp
}

define i1 @non_zero_diff_implies_icmp_ult(i8 %p0, i8 %p1) {
; CHECK-LABEL: define i1 @non_zero_diff_implies_icmp_ult(
; CHECK-SAME: i8 [[P0:%.*]], i8 [[P1:%.*]]) {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[DIFF:%.*]] = sub i8 [[P0]], [[P1]]
; CHECK-NEXT: [[COND:%.*]] = icmp eq i8 [[DIFF]], 12
; CHECK-NEXT: call void @llvm.assume(i1 [[COND]])
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[P0]], [[P1]]
; CHECK-NEXT: ret i1 [[CMP]]
;
entry:
%diff = sub i8 %p0, %p1
%cond = icmp eq i8 %diff, 12
call void @llvm.assume(i1 %cond)
%cmp = icmp ult i8 %p0, %p1
ret i1 %cmp
}