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Added inst combine tarnsform for (1 << X) & C pattrens where C is (some PowerOf2 - 1)

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This patch can handles following cases from http://nondot.org/sabre/LLVMNotes/InstCombine.txt
  "((1 << X) & 7) == 0" ==> "X > 2"
  "((1 << X) & 7) != 0" ==> "X < 3".

Differential Revision: http://reviews.llvm.org/D3678



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210007 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dinesh Dwivedi 2014-06-02 07:57:24 +00:00
parent c469e543a0
commit bcc4bce6b7
2 changed files with 41 additions and 8 deletions
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32
lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -2540,7 +2540,7 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
// bit is set. If the comparison is against zero, then this is a check
// to see if *that* bit is set.
APInt Op0KnownZeroInverted = ~Op0KnownZero;
if (~Op1KnownZero == 0 && Op0KnownZeroInverted.isPowerOf2()) {
if (~Op1KnownZero == 0) {
// If the LHS is an AND with the same constant, look through it.
Value *LHS = nullptr;
ConstantInt *LHSC = nullptr;
@ -2550,11 +2550,19 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
// If the LHS is 1 << x, and we know the result is a power of 2 like 8,
// then turn "((1 << x)&8) == 0" into "x != 3".
// or turn "((1 << x)&7) == 0" into "x > 2".
Value *X = nullptr;
if (match(LHS, m_Shl(m_One(), m_Value(X)))) {
unsigned CmpVal = Op0KnownZeroInverted.countTrailingZeros();
return new ICmpInst(ICmpInst::ICMP_NE, X,
ConstantInt::get(X->getType(), CmpVal));
APInt ValToCheck = Op0KnownZeroInverted;
if (ValToCheck.isPowerOf2()) {
unsigned CmpVal = ValToCheck.countTrailingZeros();
return new ICmpInst(ICmpInst::ICMP_NE, X,
ConstantInt::get(X->getType(), CmpVal));
} else if ((++ValToCheck).isPowerOf2()) {
unsigned CmpVal = ValToCheck.countTrailingZeros() - 1;
return new ICmpInst(ICmpInst::ICMP_UGT, X,
ConstantInt::get(X->getType(), CmpVal));
}
}
// If the LHS is 8 >>u x, and we know the result is a power of 2 like 1,
@ -2577,7 +2585,7 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
// bit is set. If the comparison is against zero, then this is a check
// to see if *that* bit is set.
APInt Op0KnownZeroInverted = ~Op0KnownZero;
if (~Op1KnownZero == 0 && Op0KnownZeroInverted.isPowerOf2()) {
if (~Op1KnownZero == 0) {
// If the LHS is an AND with the same constant, look through it.
Value *LHS = nullptr;
ConstantInt *LHSC = nullptr;
@ -2587,11 +2595,19 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
// If the LHS is 1 << x, and we know the result is a power of 2 like 8,
// then turn "((1 << x)&8) != 0" into "x == 3".
// or turn "((1 << x)&7) != 0" into "x < 3".
Value *X = nullptr;
if (match(LHS, m_Shl(m_One(), m_Value(X)))) {
unsigned CmpVal = Op0KnownZeroInverted.countTrailingZeros();
return new ICmpInst(ICmpInst::ICMP_EQ, X,
ConstantInt::get(X->getType(), CmpVal));
APInt ValToCheck = Op0KnownZeroInverted;
if (ValToCheck.isPowerOf2()) {
unsigned CmpVal = ValToCheck.countTrailingZeros();
return new ICmpInst(ICmpInst::ICMP_EQ, X,
ConstantInt::get(X->getType(), CmpVal));
} else if ((++ValToCheck).isPowerOf2()) {
unsigned CmpVal = ValToCheck.countTrailingZeros();
return new ICmpInst(ICmpInst::ICMP_ULT, X,
ConstantInt::get(X->getType(), CmpVal));
}
}
// If the LHS is 8 >>u x, and we know the result is a power of 2 like 1,

17
test/Transforms/InstCombine/icmp.ll
View File

@ -166,6 +166,14 @@ define i1 @test17(i32 %x) nounwind {
; CHECK-NEXT: %cmp = icmp ne i32 %x, 3
}
define i1 @test17a(i32 %x) nounwind {
%shl = shl i32 1, %x
%and = and i32 %shl, 7
%cmp = icmp eq i32 %and, 0
ret i1 %cmp
; CHECK-LABEL: @test17a(
; CHECK-NEXT: %cmp = icmp ugt i32 %x, 2
}
define i1 @test18(i32 %x) nounwind {
%sh = lshr i32 8, %x
@ -194,6 +202,15 @@ define i1 @test20(i32 %x) nounwind {
; CHECK-NEXT: %cmp = icmp eq i32 %x, 3
}
define i1 @test20a(i32 %x) nounwind {
%shl = shl i32 1, %x
%and = and i32 %shl, 7
%cmp = icmp ne i32 %and, 0
ret i1 %cmp
; CHECK-LABEL: @test20a(
; CHECK-NEXT: %cmp = icmp ult i32 %x, 3
}
define i1 @test21(i8 %x, i8 %y) {
; CHECK-LABEL: @test21(
; CHECK-NOT: or i8