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

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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: uaddsat, -1 fval
  %notx = xor i32 %x, -1
  %a = add i32 %x, %y
  %c = icmp ugt i32 %notx, %y
  %r = select i1 %c, i32 %a, i32 -1
  =>
  %a = add i32 %x, %y
  %c2 = icmp ugt i32 %y, %a
  %r = select i1 %c2, i32 -1, i32 %a

  Name: uaddsat, -1 fval + ult
  %notx = xor i32 %x, -1
  %a = add i32 %x, %y
  %c = icmp ult i32 %y, %notx
  %r = select i1 %c, i32 %a, i32 -1
  =>
  %a = add i32 %x, %y
  %c2 = icmp ugt i32 %y, %a
  %r = select i1 %c2, i32 -1, i32 %a

https://rise4fun.com/Alive/nTp

llvm-svn: 354276
This commit is contained in:
Sanjay Patel 2019-02-18 15:21:39 +00:00
parent c8cc085915
commit 732e40de19
2 changed files with 42 additions and 35 deletions
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45
lib/Transforms/InstCombine/InstCombineSelect.cpp
View File

@ -680,25 +680,46 @@ static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
if (!Cmp->hasOneUse())
return nullptr;
// Canonicalize to 'ULT' to simplify matching below.
Value *Cmp0 = Cmp->getOperand(0);
Value *Cmp1 = Cmp->getOperand(1);
// Match unsigned saturated add with constant.
Value *X;
const APInt *C, *CmpC;
if (match(TVal, m_Add(m_Value(X), m_APInt(C))) && X == Cmp0 &&
match(Cmp1, m_APInt(CmpC)) && *CmpC == ~*C) {
// Commute compare predicate and select operands. The backend is expecting
// this form (-1 is true value). If this changes, the backend must be
// updated too:
// (X u< ~C) ? (X + C) : -1 --> (X u> ~C) ? -1 : (X + C)
Value *NewCmp = Builder.CreateICmp(ICmpInst::ICMP_UGT, X, Cmp1);
return Builder.CreateSelect(NewCmp, FVal, TVal);
}
// Match unsigned saturated add of 2 variables with an unnecessary 'not'.
// There are 8 commuted variants.
// Canonicalize -1 (saturated result) to true value of the select.
if (match(FVal, m_AllOnes())) {
std::swap(TVal, FVal);
std::swap(Cmp0, Cmp1);
}
if (!match(TVal, m_AllOnes()))
return nullptr;
// Canonicalize predicate to 'ULT'.
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 *X, *Y;
if (match(TVal, m_AllOnes()) && match(Cmp0, m_Not(m_Value(X))) &&
Value *Y;
if (match(Cmp0, m_Not(m_Value(X))) &&
match(FVal, m_c_Add(m_Specific(X), m_Value(Y))) && Y == Cmp1) {
// Change the comparison to use the sum (false value of the select). That is
// the canonical pattern match form for uadd.with.overflow and eliminates a
// a canonical pattern match form for uadd.with.overflow and eliminates a
// use of the 'not' op:
// (~X u< Y) ? -1 : (X + Y) --> ((X + Y) u< Y) ? -1 : (X + Y)
// (~X u< Y) ? -1 : (Y + X) --> ((Y + X) u< Y) ? -1 : (Y + X)
@ -706,16 +727,6 @@ static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
return Builder.CreateSelect(NewCmp, TVal, FVal);
}
// Match unsigned saturated add with constant.
const APInt *C, *CmpC;
if (match(TVal, m_Add(m_Value(X), m_APInt(C))) && X == Cmp0 &&
match(FVal, m_AllOnes()) && match(Cmp1, m_APInt(CmpC)) && *CmpC == ~*C) {
// Commute compare predicate and select operands:
// (X u< ~C) ? (X + C) : -1 --> (X u> ~C) ? -1 : (X + C)
Value *NewCmp = Builder.CreateICmp(ICmpInst::ICMP_UGT, X, Cmp1);
return Builder.CreateSelect(NewCmp, FVal, TVal);
}
return nullptr;
}

32
test/Transforms/InstCombine/saturating-add-sub.ll
View File

@ -706,11 +706,10 @@ define <2 x i32> @uadd_sat_ugt_commute_add(<2 x i32> %xp, <2 x i32> %yp) {
define i32 @uadd_sat_commute_select(i32 %x, i32 %yp) {
; CHECK-LABEL: @uadd_sat_commute_select(
; 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 ult i32 [[Y]], [[NOTX]]
; CHECK-NEXT: [[R:%.*]] = select i1 [[C]], i32 [[A]], i32 -1
; 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
@ -724,11 +723,10 @@ define i32 @uadd_sat_commute_select_commute_add(i32 %xp, i32 %yp) {
; CHECK-LABEL: @uadd_sat_commute_select_commute_add(
; CHECK-NEXT: [[X:%.*]] = urem i32 42, [[XP:%.*]]
; CHECK-NEXT: [[Y:%.*]] = sdiv i32 [[YP:%.*]], 2442
; CHECK-NEXT: [[NOTX:%.*]] = xor i32 [[X]], -1
; CHECK-NEXT: [[A:%.*]] = add nsw i32 [[X]], [[Y]]
; CHECK-NEXT: [[C:%.*]] = icmp ult i32 [[Y]], [[NOTX]]
; CHECK-NEXT: [[R:%.*]] = select i1 [[C]], i32 [[A]], i32 -1
; 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]]
;
%x = urem i32 42, %xp ; thwart complexity-based-canonicalization
%y = sdiv i32 %yp, 2442 ; thwart complexity-based-canonicalization
@ -741,11 +739,10 @@ define i32 @uadd_sat_commute_select_commute_add(i32 %xp, i32 %yp) {
define <2 x i32> @uadd_sat_commute_select_ugt(<2 x i32> %x, <2 x i32> %y) {
; CHECK-LABEL: @uadd_sat_commute_select_ugt(
; CHECK-NEXT: [[NOTX:%.*]] = xor <2 x i32> [[X:%.*]], <i32 -1, i32 -1>
; CHECK-NEXT: [[A:%.*]] = add <2 x i32> [[Y:%.*]], [[X]]
; CHECK-NEXT: [[C:%.*]] = icmp ugt <2 x i32> [[NOTX]], [[Y]]
; CHECK-NEXT: [[R:%.*]] = select <2 x i1> [[C]], <2 x i32> [[A]], <2 x i32> <i32 -1, i32 -1>
; CHECK-NEXT: ret <2 x i32> [[R]]
; CHECK-NEXT: [[A:%.*]] = add <2 x i32> [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp ult <2 x i32> [[A]], [[Y]]
; CHECK-NEXT: [[TMP2:%.*]] = select <2 x i1> [[TMP1]], <2 x i32> <i32 -1, i32 -1>, <2 x i32> [[A]]
; CHECK-NEXT: ret <2 x i32> [[TMP2]]
;
%notx = xor <2 x i32> %x, <i32 -1, i32 -1>
%a = add <2 x i32> %y, %x
@ -757,11 +754,10 @@ define <2 x i32> @uadd_sat_commute_select_ugt(<2 x i32> %x, <2 x i32> %y) {
define i32 @uadd_sat_commute_select_ugt_commute_add(i32 %xp, i32 %y) {
; CHECK-LABEL: @uadd_sat_commute_select_ugt_commute_add(
; 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 [[NOTX]], [[Y]]
; CHECK-NEXT: [[R:%.*]] = select i1 [[C]], i32 [[A]], i32 -1
; 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]]
;
%x = srem i32 42, %xp ; thwart complexity-based-canonicalization
%notx = xor i32 %x, -1