Commit bf21f0d4 authored by David Green's avatar David Green
Browse files

[InstCombine] Extra combine for uadd_sat 

This is an extra fold for a canonical form of uadd_sat, as shown in
D68651. It essentially selects uadd from an add and a select.

Differential Revision: https://reviews.llvm.org/D69244
parent d157a9bc

llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp

+7 −0
Original line number Diff line number Diff line
@@ -781,6 +781,13 @@ static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal, 
    return Builder.CreateBinaryIntrinsic(

        Intrinsic::uadd_sat, BO->getOperand(0), BO->getOperand(1));

  }

  // The overflow may be detected via the add wrapping round.

  if (match(Cmp0, m_c_Add(m_Specific(Cmp1), m_Value(Y))) &&

      match(FVal, m_c_Add(m_Specific(Cmp1), m_Specific(Y)))) {

    // ((X + Y) u< X) ? -1 : (X + Y) --> uadd.sat(X, Y)

    // ((X + Y) u< Y) ? -1 : (X + Y) --> uadd.sat(X, Y)

    return Builder.CreateBinaryIntrinsic(Intrinsic::uadd_sat, Cmp1, Y);

  }



  return nullptr;

}

llvm/test/Transforms/InstCombine/saturating-add-sub.ll

+4 −8
Original line number Diff line number Diff line
@@ -1486,10 +1486,8 @@ define i32 @uadd_sat_constant_commute(i32 %x) { 


define i32 @uadd_sat_canon(i32 %x, i32 %y) {

; CHECK-LABEL: @uadd_sat_canon(

; CHECK-NEXT:    [[A:%.*]] = add i32 [[X:%.*]], [[Y:%.*]]

; CHECK-NEXT:    [[C:%.*]] = icmp ult i32 [[A]], [[X]]

; CHECK-NEXT:    [[R:%.*]] = select i1 [[C]], i32 -1, i32 [[A]]

; CHECK-NEXT:    ret i32 [[R]]

; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.uadd.sat.i32(i32 [[X:%.*]], i32 [[Y:%.*]])

; CHECK-NEXT:    ret i32 [[TMP1]]

;

  %a = add i32 %x, %y

  %c = icmp ult i32 %a, %x
@@ -1499,10 +1497,8 @@ define i32 @uadd_sat_canon(i32 %x, i32 %y) { 


define i32 @uadd_sat_canon_y(i32 %x, i32 %y) {

; CHECK-LABEL: @uadd_sat_canon_y(

; CHECK-NEXT:    [[A:%.*]] = add i32 [[X:%.*]], [[Y:%.*]]

; CHECK-NEXT:    [[C:%.*]] = icmp ult i32 [[A]], [[Y]]

; CHECK-NEXT:    [[R:%.*]] = select i1 [[C]], i32 -1, i32 [[A]]

; CHECK-NEXT:    ret i32 [[R]]

; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.uadd.sat.i32(i32 [[Y:%.*]], i32 [[X:%.*]])

; CHECK-NEXT:    ret i32 [[TMP1]]

;

  %a = add i32 %x, %y

  %c = icmp ult i32 %a, %y