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[InstCombine] reduce more unsigned saturated add with 'not' op 

We want to use the sum in the icmp to allow matching with
m_UAddWithOverflow and eliminate the 'not'. This is discussed
in D51929 and is another step towards solving PR14613:
https://bugs.llvm.org/show_bug.cgi?id=14613

  Name: not op
  %notx = xor i32 %x, -1
  %a = add i32 %x, %y
  %c = icmp ult i32 %notx, %y
  %r = select i1 %c, i32 -1, i32 %a
  =>
  %a = add i32 %x, %y
  %c2 = icmp ult i32 %a, %y
  %r = select i1 %c2, i32 -1, i32 %a

  Name: not op ugt
  %notx = xor i32 %x, -1
  %a = add i32 %x, %y
  %c = icmp ugt i32 %y, %notx
  %r = select i1 %c, i32 -1, i32 %a
  =>
  %a = add i32 %x, %y
  %c2 = icmp ult i32 %a, %y
  %r = select i1 %c2, i32 -1, i32 %a

https://rise4fun.com/Alive/niom

(The matching here is still incomplete.)

llvm-svn: 354224
This commit is contained in:
Sanjay Patel 2019-02-17 16:48:50 +00:00
parent db02293d9d
commit b341ee7071
2 changed files with 20 additions and 12 deletions
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16
llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
View File

@ -677,13 +677,23 @@ static Value *canonicalizeSaturatedSubtract(const ICmpInst *ICI,
static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
InstCombiner::BuilderTy &Builder) {
if (!Cmp->hasOneUse() || Cmp->getPredicate() != ICmpInst::ICMP_ULT)
if (!Cmp->hasOneUse())
return nullptr;
// Canonicalize to 'ULT' to simplify matching below.
Value *Cmp0 = Cmp->getOperand(0);
Value *Cmp1 = Cmp->getOperand(1);
ICmpInst::Predicate Pred = Cmp->getPredicate();
if (Pred == ICmpInst::ICMP_UGT) {
Pred = ICmpInst::ICMP_ULT;
std::swap(Cmp0, Cmp1);
}
if (Pred != ICmpInst::ICMP_ULT)
return nullptr;
// Match unsigned saturated add of 2 variables with an unnecessary 'not'.
// TODO: There are more variations of this pattern.
Value *Cmp0 = Cmp->getOperand(0);
Value *Cmp1 = Cmp->getOperand(1);
Value *X, *Y;
if (match(TVal, m_AllOnes()) && match(Cmp0, m_Not(m_Value(X))) &&
match(FVal, m_c_Add(m_Specific(X), m_Value(Y))) && Y == Cmp1) {

16
llvm/test/Transforms/InstCombine/saturating-add-sub.ll
View File

@ -672,11 +672,10 @@ define i32 @uadd_sat_commute_add(i32 %xp, i32 %y) {
define i32 @uadd_sat_ugt(i32 %x, i32 %yp) {
; CHECK-LABEL: @uadd_sat_ugt(
; CHECK-NEXT: [[Y:%.*]] = sdiv i32 [[YP:%.*]], 2442
; CHECK-NEXT: [[NOTX:%.*]] = xor i32 [[X:%.*]], -1
; CHECK-NEXT: [[A:%.*]] = add i32 [[Y]], [[X]]
; CHECK-NEXT: [[C:%.*]] = icmp ugt i32 [[Y]], [[NOTX]]
; CHECK-NEXT: [[R:%.*]] = select i1 [[C]], i32 -1, i32 [[A]]
; CHECK-NEXT: ret i32 [[R]]
; CHECK-NEXT: [[A:%.*]] = add i32 [[Y]], [[X:%.*]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp ult i32 [[A]], [[Y]]
; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i32 -1, i32 [[A]]
; CHECK-NEXT: ret i32 [[TMP2]]
;
%y = sdiv i32 %yp, 2442 ; thwart complexity-based-canonicalization
%notx = xor i32 %x, -1
@ -690,11 +689,10 @@ define i32 @uadd_sat_ugt_commute_add(i32 %xp, i32 %yp) {
; CHECK-LABEL: @uadd_sat_ugt_commute_add(
; CHECK-NEXT: [[Y:%.*]] = sdiv i32 [[YP:%.*]], 2442
; CHECK-NEXT: [[X:%.*]] = srem i32 42, [[XP:%.*]]
; CHECK-NEXT: [[NOTX:%.*]] = xor i32 [[X]], -1
; CHECK-NEXT: [[A:%.*]] = add i32 [[X]], [[Y]]
; CHECK-NEXT: [[C:%.*]] = icmp ugt i32 [[Y]], [[NOTX]]
; CHECK-NEXT: [[R:%.*]] = select i1 [[C]], i32 -1, i32 [[A]]
; CHECK-NEXT: ret i32 [[R]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp ult i32 [[A]], [[Y]]
; CHECK-NEXT: [[TMP2:%.*]] = select i1 [[TMP1]], i32 -1, i32 [[A]]
; CHECK-NEXT: ret i32 [[TMP2]]
;
%y = sdiv i32 %yp, 2442 ; thwart complexity-based-canonicalization
%x = srem i32 42, %xp ; thwart complexity-based-canonicalization