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Teach InstructionSimplify how to look through PHI nodes. Since PHI

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nodes can be used in loops, this could result in infinite looping
if there is no recursion limit, so add such a limit.  It is also
used for the SelectInst case because in theory there could be an
infinite loop there too if the basic block is unreachable.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@118694 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2010-11-10 18:23:01 +00:00
parent b395e4a026
commit a74a58c83b
2 changed files with 213 additions and 35 deletions
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201
lib/Analysis/InstructionSimplify.cpp
View File

@ -21,12 +21,19 @@
using namespace llvm;
using namespace llvm::PatternMatch;
#define MaxRecursionDepth 5
static Value *SimplifyBinOp(unsigned, Value *, Value *, const TargetData *,
unsigned);
static Value *SimplifyCmpInst(unsigned, Value *, Value *, const TargetData *,
unsigned);
/// ThreadBinOpOverSelect - In the case of a binary operation with a select
/// instruction as an operand, try to simplify the binop by seeing whether
/// evaluating it on both branches of the select results in the same value.
/// Returns the common value if so, otherwise returns null.
static Value *ThreadBinOpOverSelect(unsigned Opcode, Value *LHS, Value *RHS,
const TargetData *TD) {
const TargetData *TD, unsigned MaxRecurse) {
SelectInst *SI;
if (isa<SelectInst>(LHS)) {
SI = cast<SelectInst>(LHS);
@ -39,11 +46,11 @@ static Value *ThreadBinOpOverSelect(unsigned Opcode, Value *LHS, Value *RHS,
Value *TV;
Value *FV;
if (SI == LHS) {
TV = SimplifyBinOp(Opcode, SI->getTrueValue(), RHS, TD);
FV = SimplifyBinOp(Opcode, SI->getFalseValue(), RHS, TD);
TV = SimplifyBinOp(Opcode, SI->getTrueValue(), RHS, TD, MaxRecurse);
FV = SimplifyBinOp(Opcode, SI->getFalseValue(), RHS, TD, MaxRecurse);
} else {
TV = SimplifyBinOp(Opcode, LHS, SI->getTrueValue(), TD);
FV = SimplifyBinOp(Opcode, LHS, SI->getFalseValue(), TD);
TV = SimplifyBinOp(Opcode, LHS, SI->getTrueValue(), TD, MaxRecurse);
FV = SimplifyBinOp(Opcode, LHS, SI->getFalseValue(), TD, MaxRecurse);
}
// If they simplified to the same value, then return the common value.
@ -94,7 +101,8 @@ static Value *ThreadBinOpOverSelect(unsigned Opcode, Value *LHS, Value *RHS,
/// result in the same value. Returns the common value if so, otherwise returns
/// null.
static Value *ThreadCmpOverSelect(CmpInst::Predicate Pred, Value *LHS,
Value *RHS, const TargetData *TD) {
Value *RHS, const TargetData *TD,
unsigned MaxRecurse) {
// Make sure the select is on the LHS.
if (!isa<SelectInst>(LHS)) {
std::swap(LHS, RHS);
@ -105,9 +113,11 @@ static Value *ThreadCmpOverSelect(CmpInst::Predicate Pred, Value *LHS,
// Now that we have "cmp select(cond, TV, FV), RHS", analyse it.
// Does "cmp TV, RHS" simplify?
if (Value *TCmp = SimplifyCmpInst(Pred, SI->getTrueValue(), RHS, TD))
if (Value *TCmp = SimplifyCmpInst(Pred, SI->getTrueValue(), RHS, TD,
MaxRecurse))
// It does! Does "cmp FV, RHS" simplify?
if (Value *FCmp = SimplifyCmpInst(Pred, SI->getFalseValue(), RHS, TD))
if (Value *FCmp = SimplifyCmpInst(Pred, SI->getFalseValue(), RHS, TD,
MaxRecurse))
// It does! If they simplified to the same value, then use it as the
// result of the original comparison.
if (TCmp == FCmp)
@ -115,6 +125,65 @@ static Value *ThreadCmpOverSelect(CmpInst::Predicate Pred, Value *LHS,
return 0;
}
/// ThreadBinOpOverPHI - In the case of a binary operation with an operand that
/// is a PHI instruction, try to simplify the binop by seeing whether evaluating
/// it on the incoming phi values yields the same result for every value. If so
/// returns the common value, otherwise returns null.
static Value *ThreadBinOpOverPHI(unsigned Opcode, Value *LHS, Value *RHS,
const TargetData *TD, unsigned MaxRecurse) {
PHINode *PI;
if (isa<PHINode>(LHS)) {
PI = cast<PHINode>(LHS);
} else {
assert(isa<PHINode>(RHS) && "No PHI instruction operand!");
PI = cast<PHINode>(RHS);
}
// Evaluate the BinOp on the incoming phi values.
Value *CommonValue = 0;
for (unsigned i = 0, e = PI->getNumIncomingValues(); i != e; ++i) {
Value *V = PI == LHS ?
SimplifyBinOp(Opcode, PI->getIncomingValue(i), RHS, TD, MaxRecurse) :
SimplifyBinOp(Opcode, LHS, PI->getIncomingValue(i), TD, MaxRecurse);
// If the operation failed to simplify, or simplified to a different value
// to previously, then give up.
if (!V || (CommonValue && V != CommonValue))
return 0;
CommonValue = V;
}
return CommonValue;
}
/// ThreadCmpOverPHI - In the case of a comparison with a PHI instruction, try
/// try to simplify the comparison by seeing whether comparing with all of the
/// incoming phi values yields the same result every time. If so returns the
/// common result, otherwise returns null.
static Value *ThreadCmpOverPHI(CmpInst::Predicate Pred, Value *LHS, Value *RHS,
const TargetData *TD, unsigned MaxRecurse) {
// Make sure the phi is on the LHS.
if (!isa<PHINode>(LHS)) {
std::swap(LHS, RHS);
Pred = CmpInst::getSwappedPredicate(Pred);
}
assert(isa<PHINode>(LHS) && "Not comparing with a phi instruction!");
PHINode *PI = cast<PHINode>(LHS);
// Evaluate the BinOp on the incoming phi values.
Value *CommonValue = 0;
for (unsigned i = 0, e = PI->getNumIncomingValues(); i != e; ++i) {
Value *V = SimplifyCmpInst(Pred, PI->getIncomingValue(i), RHS, TD,
MaxRecurse);
// If the operation failed to simplify, or simplified to a different value
// to previously, then give up.
if (!V || (CommonValue && V != CommonValue))
return 0;
CommonValue = V;
}
return CommonValue;
}
/// SimplifyAddInst - Given operands for an Add, see if we can
/// fold the result. If not, this returns null.
Value *llvm::SimplifyAddInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
@ -146,7 +215,8 @@ Value *llvm::SimplifyAddInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
/// SimplifyAndInst - Given operands for an And, see if we can
/// fold the result. If not, this returns null.
Value *llvm::SimplifyAndInst(Value *Op0, Value *Op1, const TargetData *TD) {
static Value *SimplifyAndInst(Value *Op0, Value *Op1, const TargetData *TD,
unsigned MaxRecurse) {
if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
Constant *Ops[] = { CLHS, CRHS };
@ -212,16 +282,29 @@ Value *llvm::SimplifyAndInst(Value *Op0, Value *Op1, const TargetData *TD) {
// If the operation is with the result of a select instruction, check whether
// operating on either branch of the select always yields the same value.
if (isa<SelectInst>(Op0) || isa<SelectInst>(Op1))
if (Value *V = ThreadBinOpOverSelect(Instruction::And, Op0, Op1, TD))
if (MaxRecurse && (isa<SelectInst>(Op0) || isa<SelectInst>(Op1)))
if (Value *V = ThreadBinOpOverSelect(Instruction::And, Op0, Op1, TD,
MaxRecurse-1))
return V;
// If the operation is with the result of a phi instruction, check whether
// operating on all incoming values of the phi always yields the same value.
if (MaxRecurse && (isa<PHINode>(Op0) || isa<PHINode>(Op1)))
if (Value *V = ThreadBinOpOverPHI(Instruction::And, Op0, Op1, TD,
MaxRecurse-1))
return V;
return 0;
}
Value *llvm::SimplifyAndInst(Value *Op0, Value *Op1, const TargetData *TD) {
return ::SimplifyAndInst(Op0, Op1, TD, MaxRecursionDepth);
}
/// SimplifyOrInst - Given operands for an Or, see if we can
/// fold the result. If not, this returns null.
Value *llvm::SimplifyOrInst(Value *Op0, Value *Op1, const TargetData *TD) {
static Value *SimplifyOrInst(Value *Op0, Value *Op1, const TargetData *TD,
unsigned MaxRecurse) {
if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
Constant *Ops[] = { CLHS, CRHS };
@ -287,13 +370,24 @@ Value *llvm::SimplifyOrInst(Value *Op0, Value *Op1, const TargetData *TD) {
// If the operation is with the result of a select instruction, check whether
// operating on either branch of the select always yields the same value.
if (isa<SelectInst>(Op0) || isa<SelectInst>(Op1))
if (Value *V = ThreadBinOpOverSelect(Instruction::Or, Op0, Op1, TD))
if (MaxRecurse && (isa<SelectInst>(Op0) || isa<SelectInst>(Op1)))
if (Value *V = ThreadBinOpOverSelect(Instruction::Or, Op0, Op1, TD,
MaxRecurse-1))
return V;
// If the operation is with the result of a phi instruction, check whether
// operating on all incoming values of the phi always yields the same value.
if (MaxRecurse && (isa<PHINode>(Op0) || isa<PHINode>(Op1)))
if (Value *V = ThreadBinOpOverPHI(Instruction::Or, Op0, Op1, TD,
MaxRecurse-1))
return V;
return 0;
}
Value *llvm::SimplifyOrInst(Value *Op0, Value *Op1, const TargetData *TD) {
return ::SimplifyOrInst(Op0, Op1, TD, MaxRecursionDepth);
}
static const Type *GetCompareTy(Value *Op) {
return CmpInst::makeCmpResultType(Op->getType());
@ -301,8 +395,8 @@ static const Type *GetCompareTy(Value *Op) {
/// SimplifyICmpInst - Given operands for an ICmpInst, see if we can
/// fold the result. If not, this returns null.
Value *llvm::SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD) {
static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD, unsigned MaxRecurse) {
CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
assert(CmpInst::isIntPredicate(Pred) && "Not an integer compare!");
@ -360,17 +454,28 @@ Value *llvm::SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
// If the comparison is with the result of a select instruction, check whether
// comparing with either branch of the select always yields the same value.
if (isa<SelectInst>(LHS) || isa<SelectInst>(RHS))
if (Value *V = ThreadCmpOverSelect(Pred, LHS, RHS, TD))
if (MaxRecurse && (isa<SelectInst>(LHS) || isa<SelectInst>(RHS)))
if (Value *V = ThreadCmpOverSelect(Pred, LHS, RHS, TD, MaxRecurse-1))
return V;
// If the comparison is with the result of a phi instruction, check whether
// doing the compare with each incoming phi value yields a common result.
if (MaxRecurse && (isa<PHINode>(LHS) || isa<PHINode>(RHS)))
if (Value *V = ThreadCmpOverPHI(Pred, LHS, RHS, TD, MaxRecurse-1))
return V;
return 0;
}
Value *llvm::SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD) {
return ::SimplifyICmpInst(Predicate, LHS, RHS, TD, MaxRecursionDepth);
}
/// SimplifyFCmpInst - Given operands for an FCmpInst, see if we can
/// fold the result. If not, this returns null.
Value *llvm::SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD) {
static Value *SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD, unsigned MaxRecurse) {
CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
assert(CmpInst::isFPPredicate(Pred) && "Not an FP compare!");
@ -443,13 +548,24 @@ Value *llvm::SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
// If the comparison is with the result of a select instruction, check whether
// comparing with either branch of the select always yields the same value.
if (isa<SelectInst>(LHS) || isa<SelectInst>(RHS))
if (Value *V = ThreadCmpOverSelect(Pred, LHS, RHS, TD))
if (MaxRecurse && (isa<SelectInst>(LHS) || isa<SelectInst>(RHS)))
if (Value *V = ThreadCmpOverSelect(Pred, LHS, RHS, TD, MaxRecurse-1))
return V;
// If the comparison is with the result of a phi instruction, check whether
// doing the compare with each incoming phi value yields a common result.
if (MaxRecurse && (isa<PHINode>(LHS) || isa<PHINode>(RHS)))
if (Value *V = ThreadCmpOverPHI(Pred, LHS, RHS, TD, MaxRecurse-1))
return V;
return 0;
}
Value *llvm::SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD) {
return ::SimplifyFCmpInst(Predicate, LHS, RHS, TD, MaxRecursionDepth);
}
/// SimplifySelectInst - Given operands for a SelectInst, see if we can fold
/// the result. If not, this returns null.
Value *llvm::SimplifySelectInst(Value *CondVal, Value *TrueVal, Value *FalseVal,
@ -509,11 +625,11 @@ Value *llvm::SimplifyGEPInst(Value *const *Ops, unsigned NumOps,
/// SimplifyBinOp - Given operands for a BinaryOperator, see if we can
/// fold the result. If not, this returns null.
Value *llvm::SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS,
const TargetData *TD) {
static Value *SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS,
const TargetData *TD, unsigned MaxRecurse) {
switch (Opcode) {
case Instruction::And: return SimplifyAndInst(LHS, RHS, TD);
case Instruction::Or: return SimplifyOrInst(LHS, RHS, TD);
case Instruction::And: return SimplifyAndInst(LHS, RHS, TD, MaxRecurse);
case Instruction::Or: return SimplifyOrInst(LHS, RHS, TD, MaxRecurse);
default:
if (Constant *CLHS = dyn_cast<Constant>(LHS))
if (Constant *CRHS = dyn_cast<Constant>(RHS)) {
@ -523,23 +639,38 @@ Value *llvm::SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS,
// If the operation is with the result of a select instruction, check whether
// operating on either branch of the select always yields the same value.
if (isa<SelectInst>(LHS) || isa<SelectInst>(RHS))
if (Value *V = ThreadBinOpOverSelect(Opcode, LHS, RHS, TD))
if (MaxRecurse && (isa<SelectInst>(LHS) || isa<SelectInst>(RHS)))
if (Value *V = ThreadBinOpOverSelect(Opcode, LHS, RHS, TD, MaxRecurse-1))
return V;
// If the operation is with the result of a phi instruction, check whether
// operating on all incoming values of the phi always yields the same value.
if (MaxRecurse && (isa<PHINode>(LHS) || isa<PHINode>(RHS)))
if (Value *V = ThreadBinOpOverPHI(Opcode, LHS, RHS, TD, MaxRecurse-1))
return V;
return 0;
}
}
/// SimplifyCmpInst - Given operands for a CmpInst, see if we can
/// fold the result.
Value *llvm::SimplifyCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD) {
if (CmpInst::isIntPredicate((CmpInst::Predicate)Predicate))
return SimplifyICmpInst(Predicate, LHS, RHS, TD);
return SimplifyFCmpInst(Predicate, LHS, RHS, TD);
Value *llvm::SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS,
const TargetData *TD) {
return ::SimplifyBinOp(Opcode, LHS, RHS, TD, MaxRecursionDepth);
}
/// SimplifyCmpInst - Given operands for a CmpInst, see if we can
/// fold the result.
static Value *SimplifyCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD, unsigned MaxRecurse) {
if (CmpInst::isIntPredicate((CmpInst::Predicate)Predicate))
return SimplifyICmpInst(Predicate, LHS, RHS, TD, MaxRecurse);
return SimplifyFCmpInst(Predicate, LHS, RHS, TD, MaxRecurse);
}
Value *llvm::SimplifyCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
const TargetData *TD) {
return ::SimplifyCmpInst(Predicate, LHS, RHS, TD, MaxRecursionDepth);
}
/// SimplifyInstruction - See if we can compute a simplified version of this
/// instruction. If not, this returns null.

47
test/Transforms/InstCombine/select.ll
View File

@ -499,3 +499,50 @@ define i1 @test40(i1 %cond) {
; CHECK: @test40
; CHECK: ret i1 false
}
define i1 @test41(i1 %cond) {
%zero = alloca i32
%one = alloca i32
br i1 %cond, label %true, label %false
true:
br label %ret
false:
br label %ret
ret:
%ptr = phi i32* [ %zero, %true ] , [ %one, %false ]
%isnull = icmp eq i32* %ptr, null
ret i1 %isnull
; CHECK: @test41
; CHECK: ret i1 false
}
define i1 @test42(i1 %cond, double %x) {
br i1 %cond, label %true, label %false
true:
br label %ret
false:
br label %ret
ret:
%p = phi double [ %x, %true ], [ 0x7FF0000000000000, %false ]; RHS = +infty
%cmp = fcmp ule double %x, %p
ret i1 %cmp
; CHECK: @test42
; CHECK: ret i1 true
}
define i1 @test43(i1 %cond) {
%a = alloca i32
%b = alloca i32
%c = alloca i32
br i1 %cond, label %true, label %false
true:
br label %ret
false:
br label %ret
ret:
%p = phi i32* [ %a, %true ], [ %b, %false ]
%r = icmp eq i32* %p, %c
ret i1 %r
; CHECK: @test43
; CHECK: ret i1 false
}