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[InstCombine] rearrange saturated add folds; NFC 

This is no-functional-change-intended, but that was also
true when it was part of rL354276, and I managed to lose
2 predicates for the fold with constant...causing much bot
distress. So this time I'm adding a couple of negative tests
to avoid that.

llvm-svn: 354384
This commit is contained in:
Sanjay Patel 2019-02-19 21:46:13 +00:00
parent 9845da93e1
commit dcb93c0dda
2 changed files with 44 additions and 12 deletions
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26
llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
View File

@ -680,10 +680,22 @@ static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
if (!Cmp->hasOneUse())
return nullptr;
// Canonicalize to 'ULT' to simplify matching below.
// Match unsigned saturated add with constant.
Value *Cmp0 = Cmp->getOperand(0);
Value *Cmp1 = Cmp->getOperand(1);
ICmpInst::Predicate Pred = Cmp->getPredicate();
Value *X;
const APInt *C, *CmpC;
if (Pred == ICmpInst::ICMP_ULT &&
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);
}
// Canonicalize to 'ULT' to simplify matching below.
if (Pred == ICmpInst::ICMP_UGT) {
Pred = ICmpInst::ICMP_ULT;
std::swap(Cmp0, Cmp1);
@ -694,7 +706,7 @@ static Value *canonicalizeSaturatedAdd(ICmpInst *Cmp, Value *TVal, Value *FVal,
// Match unsigned saturated add of 2 variables with an unnecessary 'not'.
// TODO: There are more variations of this pattern.
Value *X, *Y;
Value *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) {
// Change the comparison to use the sum (false value of the select). That is
@ -706,16 +718,6 @@ 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;
}

30
llvm/test/Transforms/InstCombine/saturating-add-sub.ll
View File

@ -771,6 +771,36 @@ define i32 @uadd_sat_commute_select_ugt_commute_add(i32 %xp, i32 %y) {
ret i32 %r
}
; Negative test - make sure we have a -1 in the select.
define i32 @not_uadd_sat(i32 %x, i32 %y) {
; CHECK-LABEL: @not_uadd_sat(
; CHECK-NEXT: [[A:%.*]] = add i32 [[X:%.*]], -2
; CHECK-NEXT: [[C:%.*]] = icmp ugt i32 [[X]], 1
; CHECK-NEXT: [[R:%.*]] = select i1 [[C]], i32 [[A]], i32 [[Y:%.*]]
; CHECK-NEXT: ret i32 [[R]]
;
%a = add i32 %x, -2
%c = icmp ugt i32 %x, 1
%r = select i1 %c, i32 %a, i32 %y
ret i32 %r
}
; Negative test - make sure the predicate is 'ult'.
define i32 @not_uadd_sat2(i32 %x, i32 %y) {
; CHECK-LABEL: @not_uadd_sat2(
; CHECK-NEXT: [[A:%.*]] = add i32 [[X:%.*]], -2
; CHECK-NEXT: [[C:%.*]] = icmp ugt i32 [[X]], 1
; CHECK-NEXT: [[R:%.*]] = select i1 [[C]], i32 [[A]], i32 -1
; CHECK-NEXT: ret i32 [[R]]
;
%a = add i32 %x, -2
%c = icmp ugt i32 %x, 1
%r = select i1 %c, i32 %a, i32 -1
ret i32 %r
}
define i32 @uadd_sat_constant(i32 %x) {
; CHECK-LABEL: @uadd_sat_constant(
; CHECK-NEXT: [[A:%.*]] = add i32 [[X:%.*]], 42