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InstCombine: Optimize (1 << X) Pred CstP2 to X Pred Log2(CstP2) 

We may, after other optimizations, find ourselves with IR that looks
like:

  %shl = shl i32 1, %y
  %cmp = icmp ult i32 %shl, 32

Instead, we should just compare the shift count:

  %cmp = icmp ult i32 %y, 5

llvm-svn: 185242
This commit is contained in:
David Majnemer 2013-06-28 23:42:03 +00:00
parent bb97db3df9
commit b889e405eb
2 changed files with 177 additions and 3 deletions
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76
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -1319,10 +1319,80 @@ Instruction *InstCombiner::visitICmpInstWithInstAndIntCst(ICmpInst &ICI,
}
case Instruction::Shl: { // (icmp pred (shl X, ShAmt), CI)
ConstantInt *ShAmt = dyn_cast<ConstantInt>(LHSI->getOperand(1));
if (!ShAmt) break;
uint32_t TypeBits = RHSV.getBitWidth();
ConstantInt *ShAmt = dyn_cast<ConstantInt>(LHSI->getOperand(1));
if (!ShAmt) {
Value *X;
// (1 << X) pred P2 -> X pred Log2(P2)
if (match(LHSI, m_Shl(m_One(), m_Value(X)))) {
bool RHSVIsPowerOf2 = RHSV.isPowerOf2();
ICmpInst::Predicate Pred = ICI.getPredicate();
if (ICI.isUnsigned()) {
if (!RHSVIsPowerOf2) {
// (1 << X) < 30 -> X <= 4
// (1 << X) <= 30 -> X <= 4
// (1 << X) >= 30 -> X > 4
// (1 << X) > 30 -> X > 4
if (Pred == ICmpInst::ICMP_ULT)
Pred = ICmpInst::ICMP_ULE;
else if (Pred == ICmpInst::ICMP_UGE)
Pred = ICmpInst::ICMP_UGT;
}
unsigned RHSLog2 = RHSV.logBase2();
// (1 << X) >= 2147483648 -> X >= 31 -> X == 31
// (1 << X) > 2147483648 -> X > 31 -> false
// (1 << X) <= 2147483648 -> X <= 31 -> true
// (1 << X) < 2147483648 -> X < 31 -> X != 31
if (RHSLog2 == TypeBits-1) {
if (Pred == ICmpInst::ICMP_UGE)
Pred = ICmpInst::ICMP_EQ;
else if (Pred == ICmpInst::ICMP_UGT)
return ReplaceInstUsesWith(ICI, Builder->getFalse());
else if (Pred == ICmpInst::ICMP_ULE)
return ReplaceInstUsesWith(ICI, Builder->getTrue());
else if (Pred == ICmpInst::ICMP_ULT)
Pred = ICmpInst::ICMP_NE;
}
return new ICmpInst(Pred, X,
ConstantInt::get(RHS->getType(), RHSLog2));
} else if (ICI.isSigned()) {
if (RHSV.isAllOnesValue()) {
// (1 << X) <= -1 -> X == 31
if (Pred == ICmpInst::ICMP_SLE)
return new ICmpInst(ICmpInst::ICMP_EQ, X,
ConstantInt::get(RHS->getType(), TypeBits-1));
// (1 << X) > -1 -> X != 31
if (Pred == ICmpInst::ICMP_SGT)
return new ICmpInst(ICmpInst::ICMP_NE, X,
ConstantInt::get(RHS->getType(), TypeBits-1));
} else if (!RHSV) {
// (1 << X) < 0 -> X == 31
// (1 << X) <= 0 -> X == 31
if (Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_SLE)
return new ICmpInst(ICmpInst::ICMP_EQ, X,
ConstantInt::get(RHS->getType(), TypeBits-1));
// (1 << X) >= 0 -> X != 31
// (1 << X) > 0 -> X != 31
if (Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_SGE)
return new ICmpInst(ICmpInst::ICMP_NE, X,
ConstantInt::get(RHS->getType(), TypeBits-1));
}
} else if (ICI.isEquality()) {
if (RHSVIsPowerOf2)
return new ICmpInst(
Pred, X, ConstantInt::get(RHS->getType(), RHSV.logBase2()));
return ReplaceInstUsesWith(
ICI, Pred == ICmpInst::ICMP_EQ ? Builder->getFalse()
: Builder->getTrue());
}
}
break;
}
// Check that the shift amount is in range. If not, don't perform
// undefined shifts. When the shift is visited it will be

104
llvm/test/Transforms/InstCombine/icmp.ll
View File

@ -998,3 +998,107 @@ define i1 @test71(i8* %x) {
%c = icmp ugt i8* %a, %b
ret i1 %c
}
; CHECK: @icmp_shl_1_V_ult_32
; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp ult i32 %V, 5
; CHECK-NEXT: ret i1 [[CMP]]
define i1 @icmp_shl_1_V_ult_32(i32 %V) {
%shl = shl i32 1, %V
%cmp = icmp ult i32 %shl, 32
ret i1 %cmp
}
; CHECK: @icmp_shl_1_V_eq_32
; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp eq i32 %V, 5
; CHECK-NEXT: ret i1 [[CMP]]
define i1 @icmp_shl_1_V_eq_32(i32 %V) {
%shl = shl i32 1, %V
%cmp = icmp eq i32 %shl, 32
ret i1 %cmp
}
; CHECK: @icmp_shl_1_V_eq_31
; CHECK-NEXT: ret i1 false
define i1 @icmp_shl_1_V_eq_31(i32 %V) {
%shl = shl i32 1, %V
%cmp = icmp eq i32 %shl, 31
ret i1 %cmp
}
; CHECK: @icmp_shl_1_V_ne_31
; CHECK-NEXT: ret i1 true
define i1 @icmp_shl_1_V_ne_31(i32 %V) {
%shl = shl i32 1, %V
%cmp = icmp ne i32 %shl, 31
ret i1 %cmp
}
; CHECK: @icmp_shl_1_V_ult_30
; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp ult i32 %V, 5
; CHECK-NEXT: ret i1 [[CMP]]
define i1 @icmp_shl_1_V_ult_30(i32 %V) {
%shl = shl i32 1, %V
%cmp = icmp ult i32 %shl, 30
ret i1 %cmp
}
; CHECK: @icmp_shl_1_V_ugt_30
; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp ugt i32 %V, 4
; CHECK-NEXT: ret i1 [[CMP]]
define i1 @icmp_shl_1_V_ugt_30(i32 %V) {
%shl = shl i32 1, %V
%cmp = icmp ugt i32 %shl, 30
ret i1 %cmp
}
; CHECK: @icmp_shl_1_V_ule_30
; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp ult i32 %V, 5
; CHECK-NEXT: ret i1 [[CMP]]
define i1 @icmp_shl_1_V_ule_30(i32 %V) {
%shl = shl i32 1, %V
%cmp = icmp ule i32 %shl, 30
ret i1 %cmp
}
; CHECK: @icmp_shl_1_V_uge_30
; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp ugt i32 %V, 4
; CHECK-NEXT: ret i1 [[CMP]]
define i1 @icmp_shl_1_V_uge_30(i32 %V) {
%shl = shl i32 1, %V
%cmp = icmp uge i32 %shl, 30
ret i1 %cmp
}
; CHECK: @icmp_shl_1_V_uge_2147483648
; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp eq i32 %V, 31
; CHECK-NEXT: ret i1 [[CMP]]
define i1 @icmp_shl_1_V_uge_2147483648(i32 %V) {
%shl = shl i32 1, %V
%cmp = icmp uge i32 %shl, 2147483648
ret i1 %cmp
}
; CHECK: @icmp_shl_1_V_ugt_2147483648
; CHECK-NEXT: ret i1 false
define i1 @icmp_shl_1_V_ugt_2147483648(i32 %V) {
%shl = shl i32 1, %V
%cmp = icmp ugt i32 %shl, 2147483648
ret i1 %cmp
}
; CHECK: @icmp_shl_1_V_ule_2147483648
; CHECK-NEXT: ret i1 true
define i1 @icmp_shl_1_V_ule_2147483648(i32 %V) {
%shl = shl i32 1, %V
%cmp = icmp ule i32 %shl, 2147483648
ret i1 %cmp
}
; CHECK: @icmp_shl_1_V_ult_2147483648
; CHECK-NEXT: [[CMP:%[a-z0-9]+]] = icmp ne i32 %V, 31
; CHECK-NEXT: ret i1 [[CMP]]
define i1 @icmp_shl_1_V_ult_2147483648(i32 %V) {
%shl = shl i32 1, %V
%cmp = icmp ult i32 %shl, 2147483648
ret i1 %cmp
}