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[InstCombine] handle (X + A) % Op1 for small X, A #140369

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73d88b3
[test] precommit some tests for (X+A)%Op1
DesWurstes May 17, 2025
76171ed
[InstCombine] handle (X + A) % Op1 for small X, A
DesWurstes May 17, 2025
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18 changes: 18 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2461,6 +2461,24 @@ Instruction *InstCombinerImpl::visitURem(BinaryOperator &I) {
}
}

// For "(X + A) % Op1" and if (X u< Op1 && A u< Op1)
// => (X + A) >= Op1 ? X + A - Op1 : X + A .
Value *A = nullptr;
if (match(Op0, m_Add(m_Value(X), m_Value(A)))) {
Value *Val_X =
simplifyICmpInst(ICmpInst::ICMP_ULT, X, Op1, SQ.getWithInstruction(&I));
Value *Val_A =
simplifyICmpInst(ICmpInst::ICMP_ULT, A, Op1, SQ.getWithInstruction(&I));
if (Val_X && match(Val_X, m_One()) && Val_A && match(Val_A, m_One())) {
Value *FrozenOp0 = Op0;
if (!isGuaranteedNotToBeUndef(Op0))
FrozenOp0 = Builder.CreateFreeze(Op0, Op0->getName() + ".frozen");
Value *Cmp = Builder.CreateICmpUGE(FrozenOp0, Op1);
Value *Sub = Builder.CreateSub(FrozenOp0, Op1);
return SelectInst::Create(Cmp, Sub, FrozenOp0);
}
}

return nullptr;
}

Expand Down
200 changes: 200 additions & 0 deletions llvm/test/Transforms/InstCombine/urem-via-cmp-select.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,29 @@ define i8 @urem_assume(i8 %x, i8 %n) {
ret i8 %out
}

; https://alive2.llvm.org/ce/z/NXHJJD
define i8 @urem_assume_a(i8 %x, i8 %n, i8 %a) {
; CHECK-LABEL: @urem_assume_a(
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[X_FR:%.*]], [[N:%.*]]
; CHECK-NEXT: tail call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[CMP_A:%.*]] = icmp ult i8 [[A:%.*]], [[N]]
; CHECK-NEXT: tail call void @llvm.assume(i1 [[CMP_A]])
; CHECK-NEXT: [[ADD:%.*]] = add nuw i8 [[X_FR]], [[A]]
; CHECK-NEXT: [[ADD_FROZEN:%.*]] = freeze i8 [[ADD]]
; CHECK-NEXT: [[DOTNOT:%.*]] = icmp ult i8 [[ADD_FROZEN]], [[N]]
; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[DOTNOT]], i8 0, i8 [[N]]
; CHECK-NEXT: [[OUT:%.*]] = sub i8 [[ADD_FROZEN]], [[TMP1]]
; CHECK-NEXT: ret i8 [[OUT]]
;
%cmp = icmp ult i8 %x, %n
tail call void @llvm.assume(i1 %cmp)
%cmp_a = icmp ult i8 %a, %n
tail call void @llvm.assume(i1 %cmp_a)
%add = add nuw i8 %x, %a
%out = urem i8 %add, %n
ret i8 %out
}

; https://alive2.llvm.org/ce/z/MGgtYN
define i8 @urem_assume_without_nuw(i8 %x, i8 %n) {
; CHECK-LABEL: @urem_assume_without_nuw(
Expand Down Expand Up @@ -53,6 +76,48 @@ define i8 @urem_assume_eq(i8 %x, i8 %n) {
ret i8 %out
}

; Negative test: The assume is false
define i8 @urem_assume_eq_x(i8 %x, i8 %n, i8 %a) {
; CHECK-LABEL: @urem_assume_eq_x(
; CHECK-NEXT: [[CMP:%.*]] = icmp eq i8 [[X:%.*]], [[N:%.*]]
; CHECK-NEXT: tail call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[CMP_A:%.*]] = icmp ult i8 [[A:%.*]], [[N]]
; CHECK-NEXT: tail call void @llvm.assume(i1 [[CMP_A]])
; CHECK-NEXT: [[ADD:%.*]] = add i8 [[X]], 1
; CHECK-NEXT: [[OUT:%.*]] = urem i8 [[ADD]], [[N]]
; CHECK-NEXT: ret i8 [[OUT]]
;
%cmp = icmp eq i8 %x, %n
tail call void @llvm.assume(i1 %cmp)
%cmp_a = icmp ult i8 %a, %n
tail call void @llvm.assume(i1 %cmp_a)
%add = add i8 %x, 1
%out = urem i8 %add, %n
ret i8 %out
}

; Negative test: The assume is false
define i8 @urem_assume_eq_a(i8 %x, i8 %n, i8 %a) {
; CHECK-LABEL: @urem_assume_eq_a(
; CHECK-NEXT: [[X_FR:%.*]] = freeze i8 [[X:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[X_FR]], [[N:%.*]]
; CHECK-NEXT: tail call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[CMP_A:%.*]] = icmp eq i8 [[A:%.*]], [[N]]
; CHECK-NEXT: tail call void @llvm.assume(i1 [[CMP_A]])
; CHECK-NEXT: [[ADD:%.*]] = add i8 [[X_FR]], 1
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i8 [[ADD]], [[N]]
; CHECK-NEXT: [[OUT:%.*]] = select i1 [[TMP1]], i8 0, i8 [[ADD]]
; CHECK-NEXT: ret i8 [[OUT]]
;
%cmp = icmp ult i8 %x, %n
tail call void @llvm.assume(i1 %cmp)
%cmp_a = icmp eq i8 %a, %n
tail call void @llvm.assume(i1 %cmp_a)
%add = add i8 %x, 1
%out = urem i8 %add, %n
ret i8 %out
}

; Negative test: The assume is false
define i8 @urem_assume_ne(i8 %x, i8 %n) {
; CHECK-LABEL: @urem_assume_ne(
Expand All @@ -71,6 +136,52 @@ start:
ret i8 %out
}

; Negative test: The assume is false
define i8 @urem_assume_ne_x(i8 %x, i8 %n, i8 %a) {
; CHECK-LABEL: @urem_assume_ne_x(
; CHECK-NEXT: start:
; CHECK-NEXT: [[CMP:%.*]] = icmp ne i8 [[X:%.*]], [[N:%.*]]
; CHECK-NEXT: tail call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[CMP_A:%.*]] = icmp ult i8 [[A:%.*]], [[N]]
; CHECK-NEXT: tail call void @llvm.assume(i1 [[CMP_A]])
; CHECK-NEXT: [[ADD:%.*]] = add i8 [[X]], 1
; CHECK-NEXT: [[OUT:%.*]] = urem i8 [[ADD]], [[N]]
; CHECK-NEXT: ret i8 [[OUT]]
;
start:
%cmp = icmp ne i8 %x, %n
tail call void @llvm.assume(i1 %cmp)
%cmp_a = icmp ult i8 %a, %n
tail call void @llvm.assume(i1 %cmp_a)
%add = add i8 %x, 1
%out = urem i8 %add, %n
ret i8 %out
}

; Negative test: The assume is false
define i8 @urem_assume_ne_a(i8 %x, i8 %n, i8 %a) {
; CHECK-LABEL: @urem_assume_ne_a(
; CHECK-NEXT: start:
; CHECK-NEXT: [[X_FR:%.*]] = freeze i8 [[X:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp ult i8 [[X_FR]], [[N:%.*]]
; CHECK-NEXT: tail call void @llvm.assume(i1 [[CMP]])
; CHECK-NEXT: [[CMP_A:%.*]] = icmp ne i8 [[A:%.*]], [[N]]
; CHECK-NEXT: tail call void @llvm.assume(i1 [[CMP_A]])
; CHECK-NEXT: [[ADD:%.*]] = add i8 [[X_FR]], 1
; CHECK-NEXT: [[TMP0:%.*]] = icmp eq i8 [[ADD]], [[N]]
; CHECK-NEXT: [[OUT:%.*]] = select i1 [[TMP0]], i8 0, i8 [[ADD]]
; CHECK-NEXT: ret i8 [[OUT]]
;
start:
%cmp = icmp ult i8 %x, %n
tail call void @llvm.assume(i1 %cmp)
%cmp_a = icmp ne i8 %a, %n
tail call void @llvm.assume(i1 %cmp_a)
%add = add i8 %x, 1
%out = urem i8 %add, %n
ret i8 %out
}

; Negative test: The add constant is not 1
define i8 @urem_assume_with_unexpected_const(i8 %x, i8 %n) {
; CHECK-LABEL: @urem_assume_with_unexpected_const(
Expand Down Expand Up @@ -103,6 +214,39 @@ define i8 @urem_without_assume(i8 %arg, i8 %arg2) {
ret i8 %out
}

; Negative test: The add constant is not less than %arg2
define i8 @urem_without_assume_a_var(i8 %arg, i8 %arg2, i8 %a) {
; CHECK-LABEL: @urem_without_assume_a_var(
; CHECK-NEXT: [[X:%.*]] = urem i8 [[ARG:%.*]], [[ARG2:%.*]]
; CHECK-NEXT: [[ADD:%.*]] = add i8 [[X]], [[A:%.*]]
; CHECK-NEXT: [[OUT:%.*]] = urem i8 [[ADD]], [[ARG2]]
; CHECK-NEXT: ret i8 [[OUT]]
;
%x = urem i8 %arg, %arg2
%add = add i8 %x, %a
%out = urem i8 %add, %arg2
ret i8 %out
}

; https://alive2.llvm.org/ce/z/tcdf4d
define i8 @urem_without_assume_a(i8 %arg, i8 %arg2, i8 %a) {
; CHECK-LABEL: @urem_without_assume_a(
; CHECK-NEXT: [[X_REM:%.*]] = urem i8 [[ARG:%.*]], [[ARG2:%.*]]
; CHECK-NEXT: [[A_REM:%.*]] = urem i8 [[A:%.*]], [[ARG2]]
; CHECK-NEXT: [[ADDD:%.*]] = add i8 [[X_REM]], [[A_REM]]
; CHECK-NEXT: [[ADD_FROZEN:%.*]] = freeze i8 [[ADDD]]
; CHECK-NEXT: [[DOTNOT:%.*]] = icmp ult i8 [[ADD_FROZEN]], [[ARG2]]
; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[DOTNOT]], i8 0, i8 [[ARG2]]
; CHECK-NEXT: [[OUT:%.*]] = sub i8 [[ADD_FROZEN]], [[TMP1]]
; CHECK-NEXT: ret i8 [[OUT]]
;
%x_rem = urem i8 %arg, %arg2
%a_rem = urem i8 %a, %arg2
%add = add i8 %x_rem, %a_rem
%out = urem i8 %add, %arg2
ret i8 %out
}

; https://alive2.llvm.org/ce/z/eHkgRa
define i8 @urem_with_dominating_condition(i8 %x, i8 %n) {
; CHECK-LABEL: @urem_with_dominating_condition(
Expand Down Expand Up @@ -177,4 +321,60 @@ define noundef i8 @urem_with_opposite_condition(i8 %x, i8 %n) {
ret i8 0
}

; Negative test
define noundef i8 @urem_with_opposite_condition_x(i8 %x, i8 %n, i8 %a) {
; CHECK-LABEL: @urem_with_opposite_condition_x(
; CHECK-NEXT: [[COND:%.*]] = icmp ult i8 [[X:%.*]], [[N:%.*]]
; CHECK-NEXT: br i1 [[COND]], label [[DOTBB2:%.*]], label [[DOTBB0:%.*]]
; CHECK: .bb0:
; CHECK-NEXT: [[COND2:%.*]] = icmp ult i8 [[A:%.*]], [[N]]
; CHECK-NEXT: br i1 [[COND2]], label [[DOTBB1:%.*]], label [[DOTBB2]]
; CHECK: .bb1:
; CHECK-NEXT: [[ADD:%.*]] = add i8 [[X]], [[A]]
; CHECK-NEXT: [[OUT:%.*]] = urem i8 [[ADD]], [[N]]
; CHECK-NEXT: ret i8 [[OUT]]
; CHECK: .bb2:
; CHECK-NEXT: ret i8 0
;
%cond = icmp ult i8 %x, %n
br i1 %cond, label %.bb2, label %.bb0 ; Revert the condition
.bb0:
%cond2 = icmp ult i8 %a, %n
br i1 %cond2, label %.bb1, label %.bb2
.bb1:
%add = add i8 %x, %a
%out = urem i8 %add, %n
ret i8 %out
.bb2:
ret i8 0
}

; Negative test
define noundef i8 @urem_with_opposite_condition_a(i8 %x, i8 %n, i8 %a) {
; CHECK-LABEL: @urem_with_opposite_condition_a(
; CHECK-NEXT: [[COND:%.*]] = icmp ult i8 [[X:%.*]], [[N:%.*]]
; CHECK-NEXT: br i1 [[COND]], label [[DOTBB0:%.*]], label [[DOTBB2:%.*]]
; CHECK: .bb0:
; CHECK-NEXT: [[COND2:%.*]] = icmp ult i8 [[A:%.*]], [[N]]
; CHECK-NEXT: br i1 [[COND2]], label [[DOTBB2]], label [[DOTBB1:%.*]]
; CHECK: .bb1:
; CHECK-NEXT: [[ADD:%.*]] = add i8 [[X]], [[A]]
; CHECK-NEXT: [[OUT:%.*]] = urem i8 [[ADD]], [[N]]
; CHECK-NEXT: ret i8 [[OUT]]
; CHECK: .bb2:
; CHECK-NEXT: ret i8 0
;
%cond = icmp ult i8 %x, %n
br i1 %cond, label %.bb0, label %.bb2
.bb0:
%cond2 = icmp ult i8 %a, %n
br i1 %cond2, label %.bb2, label %.bb1 ; Revert the condition
.bb1:
%add = add i8 %x, %a
%out = urem i8 %add, %n
ret i8 %out
.bb2:
ret i8 0
}

declare void @llvm.assume(i1 noundef)
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