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InstCombine: Match min/max hidden by sext/zext
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X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X
X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X
X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X
X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X
X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X
X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X

Instead of calculating this with mixed types promote all to the
larger type. This enables scalar evolution to analyze this
expression. PR8866

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123034 91177308-0d34-0410-b5e6-96231b3b80d8
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@tobiasgrosser
tobiasgrosser committed Jan 7, 2011
1 parent 8d088bd commit 46431d7
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Showing 2 changed files with 152 additions and 35 deletions.
105 changes: 70 additions & 35 deletions lib/Transforms/InstCombine/InstCombineSelect.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -285,48 +285,83 @@ Instruction *InstCombiner::visitSelectInstWithICmp(SelectInst &SI,
// place here, so make sure the select is the only user.
if (ICI->hasOneUse())
if (ConstantInt *CI = dyn_cast<ConstantInt>(CmpRHS)) {
// X < MIN ? T : F --> F
if ((Pred == ICmpInst::ICMP_SLT || Pred == ICmpInst::ICMP_ULT)
&& CI->isMinValue(Pred == ICmpInst::ICMP_SLT))
return ReplaceInstUsesWith(SI, FalseVal);
// X > MAX ? T : F --> F
else if ((Pred == ICmpInst::ICMP_SGT || Pred == ICmpInst::ICMP_UGT)
&& CI->isMaxValue(Pred == ICmpInst::ICMP_SGT))
return ReplaceInstUsesWith(SI, FalseVal);
switch (Pred) {
default: break;
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_SLT: {
// X < MIN ? T : F --> F
if (CI->isMinValue(Pred == ICmpInst::ICMP_SLT))
return ReplaceInstUsesWith(SI, FalseVal);
// X < C ? X : C-1 --> X > C-1 ? C-1 : X
Constant *AdjustedRHS =
ConstantInt::get(CI->getContext(), CI->getValue()-1);
if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
(CmpLHS == FalseVal && AdjustedRHS == TrueVal)) {
Pred = ICmpInst::getSwappedPredicate(Pred);
CmpRHS = AdjustedRHS;
std::swap(FalseVal, TrueVal);
ICI->setPredicate(Pred);
ICI->setOperand(1, CmpRHS);
SI.setOperand(1, TrueVal);
SI.setOperand(2, FalseVal);
Changed = true;
}
break;
}
case ICmpInst::ICMP_SLT:
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_SGT: {
// X > MAX ? T : F --> F
if (CI->isMaxValue(Pred == ICmpInst::ICMP_SGT))
return ReplaceInstUsesWith(SI, FalseVal);
Constant *AdjustedRHS;
if (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_SGT)
AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() + 1);
else // (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_SLT)
AdjustedRHS = ConstantInt::get(CI->getContext(), CI->getValue() - 1);

// X > C ? X : C+1 --> X < C+1 ? C+1 : X
Constant *AdjustedRHS =
ConstantInt::get(CI->getContext(), CI->getValue()+1);
// X < C ? X : C-1 --> X > C-1 ? C-1 : X
if ((CmpLHS == TrueVal && AdjustedRHS == FalseVal) ||
(CmpLHS == FalseVal && AdjustedRHS == TrueVal)) {
Pred = ICmpInst::getSwappedPredicate(Pred);
CmpRHS = AdjustedRHS;
std::swap(FalseVal, TrueVal);
ICI->setPredicate(Pred);
ICI->setOperand(1, CmpRHS);
SI.setOperand(1, TrueVal);
SI.setOperand(2, FalseVal);
Changed = true;
}
(CmpLHS == FalseVal && AdjustedRHS == TrueVal))
; // Nothing to do here. Values match without any sign/zero extension.

// Types do not match. Instead of calculating this with mixed types
// promote all to the larger type. This enables scalar evolution to
// analyze this expression.
else if (CmpRHS->getType()->getScalarSizeInBits()
< SI.getType()->getScalarSizeInBits()) {
Constant *sextRHS = ConstantExpr::getSExt(AdjustedRHS,
SI.getType());

// X = sext x; x >s c ? X : C+1 --> X = sext x; X <s C+1 ? C+1 : X
// X = sext x; x <s c ? X : C-1 --> X = sext x; X >s C-1 ? C-1 : X
// X = sext x; x >u c ? X : C+1 --> X = sext x; X <u C+1 ? C+1 : X
// X = sext x; x <u c ? X : C-1 --> X = sext x; X >u C-1 ? C-1 : X
if (match(TrueVal, m_SExt(m_Specific(CmpLHS))) &&
sextRHS == FalseVal) {
CmpLHS = TrueVal;
AdjustedRHS = sextRHS;
} else if (match(FalseVal, m_SExt(m_Specific(CmpLHS))) &&
sextRHS == TrueVal) {
CmpLHS = FalseVal;
AdjustedRHS = sextRHS;
} else if (ICI->isUnsigned()) {
Constant *zextRHS = ConstantExpr::getZExt(AdjustedRHS,
SI.getType());
// X = zext x; x >u c ? X : C+1 --> X = zext x; X <u C+1 ? C+1 : X
// X = zext x; x <u c ? X : C-1 --> X = zext x; X >u C-1 ? C-1 : X
// zext + signed compare cannot be changed:
// 0xff <s 0x00, but 0x00ff >s 0x0000
if (match(TrueVal, m_ZExt(m_Specific(CmpLHS))) &&
zextRHS == FalseVal) {
CmpLHS = TrueVal;
AdjustedRHS = zextRHS;
} else if (match(FalseVal, m_ZExt(m_Specific(CmpLHS))) &&
zextRHS == TrueVal) {
CmpLHS = FalseVal;
AdjustedRHS = zextRHS;
} else
break;
} else
break;
} else
break;

Pred = ICmpInst::getSwappedPredicate(Pred);
CmpRHS = AdjustedRHS;
std::swap(FalseVal, TrueVal);
ICI->setPredicate(Pred);
ICI->setOperand(0, CmpLHS);
ICI->setOperand(1, CmpRHS);
SI.setOperand(1, TrueVal);
SI.setOperand(2, FalseVal);
Changed = true;
break;
}
}
Expand Down
82 changes: 82 additions & 0 deletions test/Transforms/InstCombine/select.ll
View file
Original file line number Diff line number Diff line change
Expand Up @@ -596,3 +596,85 @@ define i32 @test42(i32 %x, i32 %y) {
; CHECK-NEXT: %c = add i32 %b, %y
; CHECK-NEXT: ret i32 %c
}

define i64 @test43(i32 %a) nounwind {
%a_ext = sext i32 %a to i64
%is_a_nonnegative = icmp sgt i32 %a, -1
%max = select i1 %is_a_nonnegative, i64 %a_ext, i64 0
ret i64 %max
; CHECK: @test43
; CHECK-NEXT: %a_ext = sext i32 %a to i64
; CHECK-NEXT: %is_a_nonnegative = icmp slt i64 %a_ext, 0
; CHECK-NEXT: %max = select i1 %is_a_nonnegative, i64 0, i64 %a_ext
; CHECK-NEXT: ret i64 %max
}

define i64 @test44(i32 %a) nounwind {
%a_ext = sext i32 %a to i64
%is_a_nonpositive = icmp slt i32 %a, 1
%min = select i1 %is_a_nonpositive, i64 %a_ext, i64 0
ret i64 %min
; CHECK: @test44
; CHECK-NEXT: %a_ext = sext i32 %a to i64
; CHECK-NEXT: %is_a_nonpositive = icmp sgt i64 %a_ext, 0
; CHECK-NEXT: %min = select i1 %is_a_nonpositive, i64 0, i64 %a_ext
; CHECK-NEXT: ret i64 %min
}
define i64 @test45(i32 %a) nounwind {
%a_ext = zext i32 %a to i64
%is_a_nonnegative = icmp ugt i32 %a, 2
%max = select i1 %is_a_nonnegative, i64 %a_ext, i64 3
ret i64 %max
; CHECK: @test45
; CHECK-NEXT: %a_ext = zext i32 %a to i64
; CHECK-NEXT: %is_a_nonnegative = icmp ult i64 %a_ext, 3
; CHECK-NEXT: %max = select i1 %is_a_nonnegative, i64 3, i64 %a_ext
; CHECK-NEXT: ret i64 %max
}

define i64 @test46(i32 %a) nounwind {
%a_ext = zext i32 %a to i64
%is_a_nonpositive = icmp ult i32 %a, 3
%min = select i1 %is_a_nonpositive, i64 %a_ext, i64 2
ret i64 %min
; CHECK: @test46
; CHECK-NEXT: %a_ext = zext i32 %a to i64
; CHECK-NEXT: %is_a_nonpositive = icmp ugt i64 %a_ext, 2
; CHECK-NEXT: %min = select i1 %is_a_nonpositive, i64 2, i64 %a_ext
; CHECK-NEXT: ret i64 %min
}
define i64 @test47(i32 %a) nounwind {
%a_ext = sext i32 %a to i64
%is_a_nonnegative = icmp ugt i32 %a, 2
%max = select i1 %is_a_nonnegative, i64 %a_ext, i64 3
ret i64 %max
; CHECK: @test47
; CHECK-NEXT: %a_ext = sext i32 %a to i64
; CHECK-NEXT: %is_a_nonnegative = icmp ult i64 %a_ext, 3
; CHECK-NEXT: %max = select i1 %is_a_nonnegative, i64 3, i64 %a_ext
; CHECK-NEXT: ret i64 %max
}

define i64 @test48(i32 %a) nounwind {
%a_ext = sext i32 %a to i64
%is_a_nonpositive = icmp ult i32 %a, 3
%min = select i1 %is_a_nonpositive, i64 %a_ext, i64 2
ret i64 %min
; CHECK: @test48
; CHECK-NEXT: %a_ext = sext i32 %a to i64
; CHECK-NEXT: %is_a_nonpositive = icmp ugt i64 %a_ext, 2
; CHECK-NEXT: %min = select i1 %is_a_nonpositive, i64 2, i64 %a_ext
; CHECK-NEXT: ret i64 %min
}

define i64 @test49(i32 %a) nounwind {
%a_ext = sext i32 %a to i64
%is_a_nonpositive = icmp ult i32 %a, 3
%min = select i1 %is_a_nonpositive, i64 2, i64 %a_ext
ret i64 %min
; CHECK: @test49
; CHECK-NEXT: %a_ext = sext i32 %a to i64
; CHECK-NEXT: %is_a_nonpositive = icmp ugt i64 %a_ext, 2
; CHECK-NEXT: %min = select i1 %is_a_nonpositive, i64 %a_ext, i64 2
; CHECK-NEXT: ret i64 %min
}

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