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[InstCombine] fold urem with sext bool divisor 

Similar to other patches in this series:
https://reviews.llvm.org/rL335512
https://reviews.llvm.org/rL335527
https://reviews.llvm.org/rL335597
https://reviews.llvm.org/rL335616

...this is filling a gap in analysis that is exposed by an unrelated select-of-constants transform.
I didn't see a way to unify the sext cases because each div/rem opcode results in a different fold.

Note that in this case, the backend might want to convert the select into math:
Name: sext urem
%e = sext i1 %x to i32
%r = urem i32 %y, %e
=>
%c = icmp eq i32 %y, -1
%z = zext i1 %c to i32
%r = add i32 %z, %y

llvm-svn: 335622
This commit is contained in:
Sanjay Patel 2018-06-26 16:30:00 +00:00
parent bbfc18b5b5
commit 3575f0c0b3
2 changed files with 17 additions and 6 deletions
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15
llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
View File

@ -1295,8 +1295,9 @@ Instruction *InstCombiner::visitURem(BinaryOperator &I) {
// X urem Y -> X and Y-1, where Y is a power of 2,
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
Type *Ty = I.getType();
if (isKnownToBeAPowerOfTwo(Op1, /*OrZero*/ true, 0, &I)) {
Constant *N1 = Constant::getAllOnesValue(I.getType());
Constant *N1 = Constant::getAllOnesValue(Ty);
Value *Add = Builder.CreateAdd(Op1, N1);
return BinaryOperator::CreateAnd(Op0, Add);
}
@ -1304,7 +1305,7 @@ Instruction *InstCombiner::visitURem(BinaryOperator &I) {
// 1 urem X -> zext(X != 1)
if (match(Op0, m_One())) {
Value *Cmp = Builder.CreateICmpNE(Op1, Op0);
Value *Ext = Builder.CreateZExt(Cmp, I.getType());
Value *Ext = Builder.CreateZExt(Cmp, Ty);
return replaceInstUsesWith(I, Ext);
}
@ -1315,6 +1316,16 @@ Instruction *InstCombiner::visitURem(BinaryOperator &I) {
return SelectInst::Create(Cmp, Op0, Sub);
}
// If the divisor is a sext of a boolean, then the divisor must be max
// unsigned value (-1). Therefore, the remainder is Op0 unless Op0 is also
// max unsigned value. In that case, the remainder is 0:
// urem Op0, (sext i1 X) --> (Op0 == -1) ? 0 : Op0
Value *X;
if (match(Op1, m_SExt(m_Value(X))) && X->getType()->isIntOrIntVectorTy(1)) {
Value *Cmp = Builder.CreateICmpEQ(Op0, ConstantInt::getAllOnesValue(Ty));
return SelectInst::Create(Cmp, ConstantInt::getNullValue(Ty), Op0);
}
return nullptr;
}

8
llvm/test/Transforms/InstCombine/rem.ll
View File

@ -60,8 +60,8 @@ define i5 @biggest_divisor(i5 %x) {
define i8 @urem_with_sext_bool_divisor(i1 %x, i8 %y) {
; CHECK-LABEL: @urem_with_sext_bool_divisor(
; CHECK-NEXT: [[S:%.*]] = sext i1 [[X:%.*]] to i8
; CHECK-NEXT: [[REM:%.*]] = urem i8 [[Y:%.*]], [[S]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq i8 [[Y:%.*]], -1
; CHECK-NEXT: [[REM:%.*]] = select i1 [[TMP1]], i8 0, i8 [[Y]]
; CHECK-NEXT: ret i8 [[REM]]
;
%s = sext i1 %x to i8
@ -71,8 +71,8 @@ define i8 @urem_with_sext_bool_divisor(i1 %x, i8 %y) {
define <2 x i8> @urem_with_sext_bool_divisor_vec(<2 x i1> %x, <2 x i8> %y) {
; CHECK-LABEL: @urem_with_sext_bool_divisor_vec(
; CHECK-NEXT: [[S:%.*]] = sext <2 x i1> [[X:%.*]] to <2 x i8>
; CHECK-NEXT: [[REM:%.*]] = urem <2 x i8> [[Y:%.*]], [[S]]
; CHECK-NEXT: [[TMP1:%.*]] = icmp eq <2 x i8> [[Y:%.*]], <i8 -1, i8 -1>
; CHECK-NEXT: [[REM:%.*]] = select <2 x i1> [[TMP1]], <2 x i8> zeroinitializer, <2 x i8> [[Y]]
; CHECK-NEXT: ret <2 x i8> [[REM]]
;
%s = sext <2 x i1> %x to <2 x i8>