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[InstCombine] X | C == C --> (X & ~C) == 0 

We should canonicalize to one of these forms,
and compare-with-zero could be more conducive
to follow-on transforms. This also leads to
generally better codegen as shown in PR40611:
https://bugs.llvm.org/show_bug.cgi?id=40611

llvm-svn: 353313
This commit is contained in:
Sanjay Patel 2019-02-06 16:43:54 +00:00
parent 51abb86f09
commit 68bc5fb0ad
2 changed files with 26 additions and 17 deletions
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19
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -1771,13 +1771,22 @@ Instruction *InstCombiner::foldICmpOrConstant(ICmpInst &Cmp, BinaryOperator *Or,
ConstantInt::get(V->getType(), 1));
}
Value *OrOp0 = Or->getOperand(0), *OrOp1 = Or->getOperand(1);
if (Cmp.isEquality() && Cmp.getOperand(1) == OrOp1) {
// X | C == C --> X <=u C
// X | C != C --> X >u C
// iff C+1 is a power of 2 (C is a bitmask of the low bits)
if (Cmp.isEquality() && Cmp.getOperand(1) == Or->getOperand(1) &&
(C + 1).isPowerOf2()) {
if ((C + 1).isPowerOf2()) {
Pred = (Pred == CmpInst::ICMP_EQ) ? CmpInst::ICMP_ULE : CmpInst::ICMP_UGT;
return new ICmpInst(Pred, Or->getOperand(0), Or->getOperand(1));
return new ICmpInst(Pred, OrOp0, OrOp1);
}
// More general: are all bits outside of a mask constant set or not set?
// X | C == C --> (X & ~C) == 0
// X | C != C --> (X & ~C) != 0
if (Or->hasOneUse()) {
Value *A = Builder.CreateAnd(OrOp0, ~C);
return new ICmpInst(Pred, A, ConstantInt::getNullValue(OrOp0->getType()));
}
}
if (!Cmp.isEquality() || !C.isNullValue() || !Or->hasOneUse())
@ -1798,8 +1807,8 @@ Instruction *InstCombiner::foldICmpOrConstant(ICmpInst &Cmp, BinaryOperator *Or,
// Are we using xors to bitwise check for a pair of (in)equalities? Convert to
// a shorter form that has more potential to be folded even further.
Value *X1, *X2, *X3, *X4;
if (match(Or->getOperand(0), m_OneUse(m_Xor(m_Value(X1), m_Value(X2)))) &&
match(Or->getOperand(1), m_OneUse(m_Xor(m_Value(X3), m_Value(X4))))) {
if (match(OrOp0, m_OneUse(m_Xor(m_Value(X1), m_Value(X2)))) &&
match(OrOp1, m_OneUse(m_Xor(m_Value(X3), m_Value(X4))))) {
// ((X1 ^ X2) || (X3 ^ X4)) == 0 --> (X1 == X2) && (X3 == X4)
// ((X1 ^ X2) || (X3 ^ X4)) != 0 --> (X1 != X2) || (X3 != X4)
Value *Cmp12 = Builder.CreateICmp(Pred, X1, X2);

16
llvm/test/Transforms/InstCombine/icmp.ll
View File

@ -2169,8 +2169,8 @@ define <2 x i1> @or63_ne63_vec(<2 x i8> %x) {
define i1 @orC_eqC(i32 %x) {
; CHECK-LABEL: @orC_eqC(
; CHECK-NEXT: [[T0:%.*]] = or i32 [[X:%.*]], 42
; CHECK-NEXT: [[T1:%.*]] = icmp eq i32 [[T0]], 42
; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[X:%.*]], -43
; CHECK-NEXT: [[T1:%.*]] = icmp eq i32 [[TMP1]], 0
; CHECK-NEXT: ret i1 [[T1]]
;
%t0 = or i32 %x, 42
@ -2182,8 +2182,8 @@ define i1 @orC_eqC(i32 %x) {
define <2 x i1> @orC_eqC_vec(<2 x i8> %x) {
; CHECK-LABEL: @orC_eqC_vec(
; CHECK-NEXT: [[T0:%.*]] = or <2 x i8> [[X:%.*]], <i8 43, i8 43>
; CHECK-NEXT: [[T1:%.*]] = icmp eq <2 x i8> [[T0]], <i8 43, i8 43>
; CHECK-NEXT: [[TMP1:%.*]] = and <2 x i8> [[X:%.*]], <i8 -44, i8 -44>
; CHECK-NEXT: [[T1:%.*]] = icmp eq <2 x i8> [[TMP1]], zeroinitializer
; CHECK-NEXT: ret <2 x i1> [[T1]]
;
%t0 = or <2 x i8> %x, <i8 43, i8 43>
@ -2195,8 +2195,8 @@ define <2 x i1> @orC_eqC_vec(<2 x i8> %x) {
define i1 @orC_neC(i32 %x) {
; CHECK-LABEL: @orC_neC(
; CHECK-NEXT: [[T0:%.*]] = or i32 [[X:%.*]], -42
; CHECK-NEXT: [[T1:%.*]] = icmp ne i32 [[T0]], -42
; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[X:%.*]], 41
; CHECK-NEXT: [[T1:%.*]] = icmp ne i32 [[TMP1]], 0
; CHECK-NEXT: ret i1 [[T1]]
;
%t0 = or i32 %x, -42
@ -2208,8 +2208,8 @@ define i1 @orC_neC(i32 %x) {
define <2 x i1> @orC_neC_vec(<2 x i8> %x) {
; CHECK-LABEL: @orC_neC_vec(
; CHECK-NEXT: [[T0:%.*]] = or <2 x i8> [[X:%.*]], <i8 -43, i8 -43>
; CHECK-NEXT: [[T1:%.*]] = icmp ne <2 x i8> [[T0]], <i8 -43, i8 -43>
; CHECK-NEXT: [[TMP1:%.*]] = and <2 x i8> [[X:%.*]], <i8 42, i8 42>
; CHECK-NEXT: [[T1:%.*]] = icmp ne <2 x i8> [[TMP1]], zeroinitializer
; CHECK-NEXT: ret <2 x i1> [[T1]]
;
%t0 = or <2 x i8> %x, <i8 -43, i8 -43>