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[InstCombine] Simplify and correct folding fcmps with the same children
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Summary: Take advantage of FCmpInst::Predicate's bit pattern and handle (fcmp *, x, y) | (fcmp *, x, y) and (fcmp *, x, y) & (fcmp *, x, y) more consistently. Also fold more FCmpInst::FCMP_FALSE and FCmpInst::FCMP_TRUE to constants.

Currently InstCombine wrongly folds (fcmp ogt, x, y) | (fcmp ord, x, y) to (fcmp ogt, x, y); this patch also fixes that.

Reviewers: spatel

Subscribers: llvm-commits, iteratee, echristo

Differential Revision: http://reviews.llvm.org/D21775

llvm-svn: 274156
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@timshen91
timshen91 committed Jun 29, 2016
1 parent 860a67e commit aec68b2
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Showing 4 changed files with 283 additions and 598 deletions.
4 changes: 4 additions & 0 deletions llvm/include/llvm/IR/InstrTypes.h
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Expand Up @@ -859,6 +859,10 @@ class CmpInst : public Instruction {
/// Values in the range 0-31 are reserved for FCmpInst, while values in the
/// range 32-64 are reserved for ICmpInst. This is necessary to ensure the
/// predicate values are not overlapping between the classes.
///
/// Some passes (e.g. InstCombine) depend on the bit-wise characteristics of
/// FCMP_* values. Changing the bit patterns requires a potential change to
/// those passes.
enum Predicate {
// Opcode U L G E Intuitive operation
FCMP_FALSE = 0, ///< 0 0 0 0 Always false (always folded)
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198 changes: 76 additions & 122 deletions llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
View file
Expand Up @@ -39,30 +39,29 @@ static inline Value *dyn_castNotVal(Value *V) {
}

/// Similar to getICmpCode but for FCmpInst. This encodes a fcmp predicate into
/// a three bit mask. It also returns whether it is an ordered predicate by
/// reference.
static unsigned getFCmpCode(FCmpInst::Predicate CC, bool &isOrdered) {
isOrdered = false;
switch (CC) {
case FCmpInst::FCMP_ORD: isOrdered = true; return 0; // 000
case FCmpInst::FCMP_UNO: return 0; // 000
case FCmpInst::FCMP_OGT: isOrdered = true; return 1; // 001
case FCmpInst::FCMP_UGT: return 1; // 001
case FCmpInst::FCMP_OEQ: isOrdered = true; return 2; // 010
case FCmpInst::FCMP_UEQ: return 2; // 010
case FCmpInst::FCMP_OGE: isOrdered = true; return 3; // 011
case FCmpInst::FCMP_UGE: return 3; // 011
case FCmpInst::FCMP_OLT: isOrdered = true; return 4; // 100
case FCmpInst::FCMP_ULT: return 4; // 100
case FCmpInst::FCMP_ONE: isOrdered = true; return 5; // 101
case FCmpInst::FCMP_UNE: return 5; // 101
case FCmpInst::FCMP_OLE: isOrdered = true; return 6; // 110
case FCmpInst::FCMP_ULE: return 6; // 110
// True -> 7
default:
// Not expecting FCMP_FALSE and FCMP_TRUE;
llvm_unreachable("Unexpected FCmp predicate!");
}
/// a four bit mask.
static unsigned getFCmpCode(FCmpInst::Predicate CC) {
assert(FCmpInst::FCMP_FALSE <= CC && CC <= FCmpInst::FCMP_TRUE &&
"Unexpected FCmp predicate!");
// Take advantage of the bit pattern of FCmpInst::Predicate here.
// U L G E
static_assert(FCmpInst::FCMP_FALSE == 0, ""); // 0 0 0 0
static_assert(FCmpInst::FCMP_OEQ == 1, ""); // 0 0 0 1
static_assert(FCmpInst::FCMP_OGT == 2, ""); // 0 0 1 0
static_assert(FCmpInst::FCMP_OGE == 3, ""); // 0 0 1 1
static_assert(FCmpInst::FCMP_OLT == 4, ""); // 0 1 0 0
static_assert(FCmpInst::FCMP_OLE == 5, ""); // 0 1 0 1
static_assert(FCmpInst::FCMP_ONE == 6, ""); // 0 1 1 0
static_assert(FCmpInst::FCMP_ORD == 7, ""); // 0 1 1 1
static_assert(FCmpInst::FCMP_UNO == 8, ""); // 1 0 0 0
static_assert(FCmpInst::FCMP_UEQ == 9, ""); // 1 0 0 1
static_assert(FCmpInst::FCMP_UGT == 10, ""); // 1 0 1 0
static_assert(FCmpInst::FCMP_UGE == 11, ""); // 1 0 1 1
static_assert(FCmpInst::FCMP_ULT == 12, ""); // 1 1 0 0
static_assert(FCmpInst::FCMP_ULE == 13, ""); // 1 1 0 1
static_assert(FCmpInst::FCMP_UNE == 14, ""); // 1 1 1 0
static_assert(FCmpInst::FCMP_TRUE == 15, ""); // 1 1 1 1
return CC;
}

/// This is the complement of getICmpCode, which turns an opcode and two
Expand All @@ -78,26 +77,16 @@ static Value *getNewICmpValue(bool Sign, unsigned Code, Value *LHS, Value *RHS,
}

/// This is the complement of getFCmpCode, which turns an opcode and two
/// operands into either a FCmp instruction. isordered is passed in to determine
/// which kind of predicate to use in the new fcmp instruction.
static Value *getFCmpValue(bool isordered, unsigned code,
Value *LHS, Value *RHS,
/// operands into either a FCmp instruction, or a true/false constant.
static Value *getFCmpValue(unsigned Code, Value *LHS, Value *RHS,
InstCombiner::BuilderTy *Builder) {
CmpInst::Predicate Pred;
switch (code) {
default: llvm_unreachable("Illegal FCmp code!");
case 0: Pred = isordered ? FCmpInst::FCMP_ORD : FCmpInst::FCMP_UNO; break;
case 1: Pred = isordered ? FCmpInst::FCMP_OGT : FCmpInst::FCMP_UGT; break;
case 2: Pred = isordered ? FCmpInst::FCMP_OEQ : FCmpInst::FCMP_UEQ; break;
case 3: Pred = isordered ? FCmpInst::FCMP_OGE : FCmpInst::FCMP_UGE; break;
case 4: Pred = isordered ? FCmpInst::FCMP_OLT : FCmpInst::FCMP_ULT; break;
case 5: Pred = isordered ? FCmpInst::FCMP_ONE : FCmpInst::FCMP_UNE; break;
case 6: Pred = isordered ? FCmpInst::FCMP_OLE : FCmpInst::FCMP_ULE; break;
case 7:
if (!isordered)
return ConstantInt::get(CmpInst::makeCmpResultType(LHS->getType()), 1);
Pred = FCmpInst::FCMP_ORD; break;
}
const auto Pred = static_cast<FCmpInst::Predicate>(Code);
assert(FCmpInst::FCMP_FALSE <= Pred && Pred <= FCmpInst::FCMP_TRUE &&
"Unexpected FCmp predicate!");
if (Pred == FCmpInst::FCMP_FALSE)
return ConstantInt::get(CmpInst::makeCmpResultType(LHS->getType()), 0);
if (Pred == FCmpInst::FCMP_TRUE)
return ConstantInt::get(CmpInst::makeCmpResultType(LHS->getType()), 1);
return Builder->CreateFCmp(Pred, LHS, RHS);
}

Expand Down Expand Up @@ -1107,6 +1096,29 @@ Value *InstCombiner::FoldAndOfICmps(ICmpInst *LHS, ICmpInst *RHS) {
/// Optimize (fcmp)&(fcmp). NOTE: Unlike the rest of instcombine, this returns
/// a Value which should already be inserted into the function.
Value *InstCombiner::FoldAndOfFCmps(FCmpInst *LHS, FCmpInst *RHS) {
Value *Op0LHS = LHS->getOperand(0), *Op0RHS = LHS->getOperand(1);
Value *Op1LHS = RHS->getOperand(0), *Op1RHS = RHS->getOperand(1);
FCmpInst::Predicate Op0CC = LHS->getPredicate(), Op1CC = RHS->getPredicate();

if (Op0LHS == Op1RHS && Op0RHS == Op1LHS) {
// Swap RHS operands to match LHS.
Op1CC = FCmpInst::getSwappedPredicate(Op1CC);
std::swap(Op1LHS, Op1RHS);
}

// Simplify (fcmp cc0 x, y) & (fcmp cc1 x, y).
// Suppose the relation between x and y is R, where R is one of
// U(1000), L(0100), G(0010) or E(0001), and CC0 and CC1 are the bitmasks for
// testing the desired relations.
//
// Since (R & CC0) and (R & CC1) are either R or 0, we actually have this:
// bool(R & CC0) && bool(R & CC1)
// = bool((R & CC0) & (R & CC1))
// = bool(R & (CC0 & CC1)) <= by re-association, commutation, and idempotency
if (Op0LHS == Op1LHS && Op0RHS == Op1RHS)
return getFCmpValue(getFCmpCode(Op0CC) & getFCmpCode(Op1CC), Op0LHS, Op0RHS,
Builder);

if (LHS->getPredicate() == FCmpInst::FCMP_ORD &&
RHS->getPredicate() == FCmpInst::FCMP_ORD) {
if (LHS->getOperand(0)->getType() != RHS->getOperand(0)->getType())
Expand All @@ -1130,56 +1142,6 @@ Value *InstCombiner::FoldAndOfFCmps(FCmpInst *LHS, FCmpInst *RHS) {
return nullptr;
}

Value *Op0LHS = LHS->getOperand(0), *Op0RHS = LHS->getOperand(1);
Value *Op1LHS = RHS->getOperand(0), *Op1RHS = RHS->getOperand(1);
FCmpInst::Predicate Op0CC = LHS->getPredicate(), Op1CC = RHS->getPredicate();


if (Op0LHS == Op1RHS && Op0RHS == Op1LHS) {
// Swap RHS operands to match LHS.
Op1CC = FCmpInst::getSwappedPredicate(Op1CC);
std::swap(Op1LHS, Op1RHS);
}

if (Op0LHS == Op1LHS && Op0RHS == Op1RHS) {
// Simplify (fcmp cc0 x, y) & (fcmp cc1 x, y).
if (Op0CC == Op1CC)
return Builder->CreateFCmp((FCmpInst::Predicate)Op0CC, Op0LHS, Op0RHS);
if (Op0CC == FCmpInst::FCMP_FALSE || Op1CC == FCmpInst::FCMP_FALSE)
return ConstantInt::get(CmpInst::makeCmpResultType(LHS->getType()), 0);
if (Op0CC == FCmpInst::FCMP_TRUE)
return Builder->CreateFCmp(Op1CC, Op0LHS, Op0RHS);
if (Op1CC == FCmpInst::FCMP_TRUE)
return Builder->CreateFCmp(Op0CC, Op0LHS, Op0RHS);

bool Op0Ordered;
bool Op1Ordered;
unsigned Op0Pred = getFCmpCode(Op0CC, Op0Ordered);
unsigned Op1Pred = getFCmpCode(Op1CC, Op1Ordered);
// uno && ord -> false
if (Op0Pred == 0 && Op1Pred == 0 && Op0Ordered != Op1Ordered)
return ConstantInt::get(CmpInst::makeCmpResultType(LHS->getType()), 0);
if (Op1Pred == 0) {
std::swap(LHS, RHS);
std::swap(Op0Pred, Op1Pred);
std::swap(Op0Ordered, Op1Ordered);
}
if (Op0Pred == 0) {
// uno && ueq -> uno && (uno || eq) -> uno
// ord && olt -> ord && (ord && lt) -> olt
if (!Op0Ordered && (Op0Ordered == Op1Ordered))
return Builder->CreateFCmp(Op0CC, Op0LHS, Op0RHS);
if (Op0Ordered && (Op0Ordered == Op1Ordered))
return Builder->CreateFCmp(Op1CC, Op0LHS, Op0RHS);

// uno && oeq -> uno && (ord && eq) -> false
if (!Op0Ordered)
return ConstantInt::get(CmpInst::makeCmpResultType(LHS->getType()), 0);
// ord && ueq -> ord && (uno || eq) -> oeq
return getFCmpValue(true, Op1Pred, Op0LHS, Op0RHS, Builder);
}
}

return nullptr;
}

Expand Down Expand Up @@ -1996,6 +1958,27 @@ Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS,
/// Optimize (fcmp)|(fcmp). NOTE: Unlike the rest of instcombine, this returns
/// a Value which should already be inserted into the function.
Value *InstCombiner::FoldOrOfFCmps(FCmpInst *LHS, FCmpInst *RHS) {
Value *Op0LHS = LHS->getOperand(0), *Op0RHS = LHS->getOperand(1);
Value *Op1LHS = RHS->getOperand(0), *Op1RHS = RHS->getOperand(1);
FCmpInst::Predicate Op0CC = LHS->getPredicate(), Op1CC = RHS->getPredicate();

if (Op0LHS == Op1RHS && Op0RHS == Op1LHS) {
// Swap RHS operands to match LHS.
Op1CC = FCmpInst::getSwappedPredicate(Op1CC);
std::swap(Op1LHS, Op1RHS);
}

// Simplify (fcmp cc0 x, y) | (fcmp cc1 x, y).
// This is a similar transformation to the one in FoldAndOfFCmps.
//
// Since (R & CC0) and (R & CC1) are either R or 0, we actually have this:
// bool(R & CC0) || bool(R & CC1)
// = bool((R & CC0) | (R & CC1))
// = bool(R & (CC0 | CC1)) <= by reversed distribution (contribution? ;)
if (Op0LHS == Op1LHS && Op0RHS == Op1RHS)
return getFCmpValue(getFCmpCode(Op0CC) | getFCmpCode(Op1CC), Op0LHS, Op0RHS,
Builder);

if (LHS->getPredicate() == FCmpInst::FCMP_UNO &&
RHS->getPredicate() == FCmpInst::FCMP_UNO &&
LHS->getOperand(0)->getType() == RHS->getOperand(0)->getType()) {
Expand All @@ -2020,35 +2003,6 @@ Value *InstCombiner::FoldOrOfFCmps(FCmpInst *LHS, FCmpInst *RHS) {
return nullptr;
}

Value *Op0LHS = LHS->getOperand(0), *Op0RHS = LHS->getOperand(1);
Value *Op1LHS = RHS->getOperand(0), *Op1RHS = RHS->getOperand(1);
FCmpInst::Predicate Op0CC = LHS->getPredicate(), Op1CC = RHS->getPredicate();

if (Op0LHS == Op1RHS && Op0RHS == Op1LHS) {
// Swap RHS operands to match LHS.
Op1CC = FCmpInst::getSwappedPredicate(Op1CC);
std::swap(Op1LHS, Op1RHS);
}
if (Op0LHS == Op1LHS && Op0RHS == Op1RHS) {
// Simplify (fcmp cc0 x, y) | (fcmp cc1 x, y).
if (Op0CC == Op1CC)
return Builder->CreateFCmp((FCmpInst::Predicate)Op0CC, Op0LHS, Op0RHS);
if (Op0CC == FCmpInst::FCMP_TRUE || Op1CC == FCmpInst::FCMP_TRUE)
return ConstantInt::get(CmpInst::makeCmpResultType(LHS->getType()), 1);
if (Op0CC == FCmpInst::FCMP_FALSE)
return Builder->CreateFCmp(Op1CC, Op0LHS, Op0RHS);
if (Op1CC == FCmpInst::FCMP_FALSE)
return Builder->CreateFCmp(Op0CC, Op0LHS, Op0RHS);
bool Op0Ordered;
bool Op1Ordered;
unsigned Op0Pred = getFCmpCode(Op0CC, Op0Ordered);
unsigned Op1Pred = getFCmpCode(Op1CC, Op1Ordered);
if (Op0Ordered == Op1Ordered) {
// If both are ordered or unordered, return a new fcmp with
// or'ed predicates.
return getFCmpValue(Op0Ordered, Op0Pred|Op1Pred, Op0LHS, Op0RHS, Builder);
}
}
return nullptr;
}

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