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Teach InstructionSimplify about distributive laws. These transforms fire

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quite often, but don't make much difference in practice presumably because
instcombine also knows them and more.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122328 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2010-12-21 13:32:22 +00:00
parent 0312a93693
commit 3421d90853
2 changed files with 180 additions and 11 deletions
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170
lib/Analysis/InstructionSimplify.cpp
View File

@ -53,8 +53,120 @@ static bool ValueDominatesPHI(Value *V, PHINode *P, const DominatorTree *DT) {
return false;
}
// SimplifyAssociativeBinOp - Generic simplifications for associative binary
// operations. Returns the simpler value, or null if none was found.
/// ExpandBinOp - Simplify "A op (B op' C)" by distributing op over op', turning
/// it into "(A op B) op' (A op C)". Here "op" is given by Opcode and "op'" is
/// given by OpcodeToExpand, while "A" corresponds to LHS and "B op' C" to RHS.
/// Also performs the transform "(A op' B) op C" -> "(A op C) op' (B op C)".
/// Returns the simplified value, or null if no simplification was performed.
static Value *ExpandBinOp(unsigned Opcode, Value *LHS, Value *RHS,
unsigned OpcodeToExpand, const TargetData *TD,
const DominatorTree *DT, unsigned MaxRecurse) {
// Recursion is always used, so bail out at once if we already hit the limit.
if (!MaxRecurse--)
return 0;
// Check whether the expression has the form "(A op' B) op C".
if (BinaryOperator *Op0 = dyn_cast<BinaryOperator>(LHS))
if (Op0->getOpcode() == OpcodeToExpand) {
// It does! Try turning it into "(A op C) op' (B op C)".
Value *A = Op0->getOperand(0), *B = Op0->getOperand(1), *C = RHS;
// Do "A op C" and "B op C" both simplify?
if (Value *L = SimplifyBinOp(Opcode, A, C, TD, DT, MaxRecurse))
if (Value *R = SimplifyBinOp(Opcode, B, C, TD, DT, MaxRecurse)) {
// They do! Return "L op' R" if it simplifies or is already available.
// If "L op' R" equals "A op' B" then "L op' R" is just the LHS.
if ((L == A && R == B) ||
(Instruction::isCommutative(OpcodeToExpand) && L == B && R == A))
return LHS;
// Otherwise return "L op' R" if it simplifies.
if (Value *V = SimplifyBinOp(OpcodeToExpand, L, R, TD, DT,MaxRecurse))
return V;
}
}
// Check whether the expression has the form "A op (B op' C)".
if (BinaryOperator *Op1 = dyn_cast<BinaryOperator>(RHS))
if (Op1->getOpcode() == OpcodeToExpand) {
// It does! Try turning it into "(A op B) op' (A op C)".
Value *A = LHS, *B = Op1->getOperand(0), *C = Op1->getOperand(1);
// Do "A op B" and "A op C" both simplify?
if (Value *L = SimplifyBinOp(Opcode, A, B, TD, DT, MaxRecurse))
if (Value *R = SimplifyBinOp(Opcode, A, C, TD, DT, MaxRecurse)) {
// They do! Return "L op' R" if it simplifies or is already available.
// If "L op' R" equals "B op' C" then "L op' R" is just the RHS.
if ((L == B && R == C) ||
(Instruction::isCommutative(OpcodeToExpand) && L == C && R == B))
return RHS;
// Otherwise return "L op' R" if it simplifies.
if (Value *V = SimplifyBinOp(OpcodeToExpand, L, R, TD, DT,MaxRecurse))
return V;
}
}
return 0;
}
/// FactorizeBinOp - Simplify "LHS Opcode RHS" by factorizing out a common term
/// using the operation OpCodeToExtract. For example, when Opcode is Add and
/// OpCodeToExtract is Mul then this tries to turn "(A*B)+(A*C)" into "A*(B+C)".
/// Returns the simplified value, or null if no simplification was performed.
static Value *FactorizeBinOp(unsigned Opcode, Value *LHS, Value *RHS,
unsigned OpcodeToExtract, const TargetData *TD,
const DominatorTree *DT, unsigned MaxRecurse) {
// Recursion is always used, so bail out at once if we already hit the limit.
if (!MaxRecurse--)
return 0;
BinaryOperator *Op0 = dyn_cast<BinaryOperator>(LHS);
BinaryOperator *Op1 = dyn_cast<BinaryOperator>(RHS);
if (!Op0 || Op0->getOpcode() != OpcodeToExtract ||
!Op1 || Op1->getOpcode() != OpcodeToExtract)
return 0;
// The expression has the form "(A op' B) op (C op' D)".
Value *A = Op0->getOperand(0); Value *B = Op0->getOperand(1);
Value *C = Op1->getOperand(0); Value *D = Op1->getOperand(1);
// Use left distributivity, i.e. "X op' (Y op Z) = (X op' Y) op (X op' Z)".
// Does the instruction have the form "(A op' B) op (A op' D)" or, in the
// commutative case, "(A op' B) op (C op' A)"?
if (A == C || (Instruction::isCommutative(OpcodeToExtract) && A == D)) {
Value *DD = A == C ? D : C;
// Form "A op' (B op DD)" if it simplifies completely.
// Does "B op DD" simplify?
if (Value *V = SimplifyBinOp(Opcode, B, DD, TD, DT, MaxRecurse)) {
// It does! Return "A op' V" if it simplifies or is already available.
// If V equals B then "A op' V" is just the LHS.
if (V == B) return LHS;
// Otherwise return "A op' V" if it simplifies.
if (Value *W = SimplifyBinOp(OpcodeToExtract, A, V, TD, DT, MaxRecurse))
return W;
}
}
// Use right distributivity, i.e. "(X op Y) op' Z = (X op' Z) op (Y op' Z)".
// Does the instruction have the form "(A op' B) op (C op' B)" or, in the
// commutative case, "(A op' B) op (B op' D)"?
if (B == D || (Instruction::isCommutative(OpcodeToExtract) && B == C)) {
Value *CC = B == D ? C : D;
// Form "(A op CC) op' B" if it simplifies completely..
// Does "A op CC" simplify?
if (Value *V = SimplifyBinOp(Opcode, A, CC, TD, DT, MaxRecurse)) {
// It does! Return "V op' B" if it simplifies or is already available.
// If V equals A then "V op' B" is just the LHS.
if (V == B) return LHS;
// Otherwise return "V op' B" if it simplifies.
if (Value *W = SimplifyBinOp(OpcodeToExtract, V, B, TD, DT, MaxRecurse))
return W;
}
}
return 0;
}
/// SimplifyAssociativeBinOp - Generic simplifications for associative binary
/// operations. Returns the simpler value, or null if none was found.
static Value *SimplifyAssociativeBinOp(unsigned Opcode, Value *LHS, Value *RHS,
const TargetData *TD,
const DominatorTree *DT,
@ -78,8 +190,7 @@ static Value *SimplifyAssociativeBinOp(unsigned Opcode, Value *LHS, Value *RHS,
if (Value *V = SimplifyBinOp(Opcode, B, C, TD, DT, MaxRecurse)) {
// It does! Return "A op V" if it simplifies or is already available.
// If V equals B then "A op V" is just the LHS.
if (V == B)
return LHS;
if (V == B) return LHS;
// Otherwise return "A op V" if it simplifies.
if (Value *W = SimplifyBinOp(Opcode, A, V, TD, DT, MaxRecurse))
return W;
@ -96,8 +207,7 @@ static Value *SimplifyAssociativeBinOp(unsigned Opcode, Value *LHS, Value *RHS,
if (Value *V = SimplifyBinOp(Opcode, A, B, TD, DT, MaxRecurse)) {
// It does! Return "V op C" if it simplifies or is already available.
// If V equals B then "V op C" is just the RHS.
if (V == B)
return RHS;
if (V == B) return RHS;
// Otherwise return "V op C" if it simplifies.
if (Value *W = SimplifyBinOp(Opcode, V, C, TD, DT, MaxRecurse))
return W;
@ -118,8 +228,7 @@ static Value *SimplifyAssociativeBinOp(unsigned Opcode, Value *LHS, Value *RHS,
if (Value *V = SimplifyBinOp(Opcode, C, A, TD, DT, MaxRecurse)) {
// It does! Return "V op B" if it simplifies or is already available.
// If V equals A then "V op B" is just the LHS.
if (V == A)
return LHS;
if (V == A) return LHS;
// Otherwise return "V op B" if it simplifies.
if (Value *W = SimplifyBinOp(Opcode, V, B, TD, DT, MaxRecurse))
return W;
@ -136,8 +245,7 @@ static Value *SimplifyAssociativeBinOp(unsigned Opcode, Value *LHS, Value *RHS,
if (Value *V = SimplifyBinOp(Opcode, C, A, TD, DT, MaxRecurse)) {
// It does! Return "B op V" if it simplifies or is already available.
// If V equals C then "B op V" is just the RHS.
if (V == C)
return RHS;
if (V == C) return RHS;
// Otherwise return "B op V" if it simplifies.
if (Value *W = SimplifyBinOp(Opcode, B, V, TD, DT, MaxRecurse))
return W;
@ -381,6 +489,11 @@ static Value *SimplifyAddInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
MaxRecurse))
return V;
// Mul distributes over Add. Try some generic simplifications based on this.
if (Value *V = FactorizeBinOp(Instruction::Add, Op0, Op1, Instruction::Mul,
TD, DT, MaxRecurse))
return V;
// Threading Add over selects and phi nodes is pointless, so don't bother.
// Threading over the select in "A + select(cond, B, C)" means evaluating
// "A+B" and "A+C" and seeing if they are equal; but they are equal if and
@ -401,7 +514,7 @@ Value *llvm::SimplifyAddInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
/// SimplifySubInst - Given operands for a Sub, see if we can
/// fold the result. If not, this returns null.
static Value *SimplifySubInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
const TargetData *TD, const DominatorTree *,
const TargetData *TD, const DominatorTree *DT,
unsigned MaxRecurse) {
if (Constant *CLHS = dyn_cast<Constant>(Op0))
if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
@ -430,6 +543,11 @@ static Value *SimplifySubInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
match(Op0, m_Add(m_Specific(Op1), m_Value(X))))
return X;
// Mul distributes over Sub. Try some generic simplifications based on this.
if (Value *V = FactorizeBinOp(Instruction::Sub, Op0, Op1, Instruction::Mul,
TD, DT, MaxRecurse))
return V;
// Threading Sub over selects and phi nodes is pointless, so don't bother.
// Threading over the select in "A - select(cond, B, C)" means evaluating
// "A-B" and "A-C" and seeing if they are equal; but they are equal if and
@ -499,6 +617,21 @@ static Value *SimplifyAndInst(Value *Op0, Value *Op1, const TargetData *TD,
MaxRecurse))
return V;
// And distributes over Or. Try some generic simplifications based on this.
if (Value *V = ExpandBinOp(Instruction::And, Op0, Op1, Instruction::Or,
TD, DT, MaxRecurse))
return V;
// And distributes over Xor. Try some generic simplifications based on this.
if (Value *V = ExpandBinOp(Instruction::And, Op0, Op1, Instruction::Xor,
TD, DT, MaxRecurse))
return V;
// Or distributes over And. Try some generic simplifications based on this.
if (Value *V = FactorizeBinOp(Instruction::And, Op0, Op1, Instruction::Or,
TD, DT, MaxRecurse))
return V;
// 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))
@ -573,6 +706,16 @@ static Value *SimplifyOrInst(Value *Op0, Value *Op1, const TargetData *TD,
MaxRecurse))
return V;
// Or distributes over And. Try some generic simplifications based on this.
if (Value *V = ExpandBinOp(Instruction::Or, Op0, Op1, Instruction::And,
TD, DT, MaxRecurse))
return V;
// And distributes over Or. Try some generic simplifications based on this.
if (Value *V = FactorizeBinOp(Instruction::Or, Op0, Op1, Instruction::And,
TD, DT, MaxRecurse))
return V;
// 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))
@ -633,6 +776,11 @@ static Value *SimplifyXorInst(Value *Op0, Value *Op1, const TargetData *TD,
MaxRecurse))
return V;
// And distributes over Xor. Try some generic simplifications based on this.
if (Value *V = FactorizeBinOp(Instruction::Xor, Op0, Op1, Instruction::And,
TD, DT, MaxRecurse))
return V;
// Threading Xor over selects and phi nodes is pointless, so don't bother.
// Threading over the select in "A ^ select(cond, B, C)" means evaluating
// "A^B" and "A^C" and seeing if they are equal; but they are equal if and

21
test/Transforms/InstSimplify/2010-12-20-Distribute.ll Normal file
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@ -0,0 +1,21 @@
; RUN: opt < %s -instsimplify -S | FileCheck %s
define i32 @factorize(i32 %x, i32 %y) {
; CHECK: @factorize
; (X | 2) & (X | 2) -> X | (1 & 2) -> X
%l = or i32 %x, 1
%r = or i32 %x, 2
%z = and i32 %l, %r
ret i32 %z
; CHECK: ret i32 %x
}
define i32 @expand(i32 %x) {
; CHECK: @expand
; ((X & 1) | 2) & 1 -> ((X & 1) & 1) | (2 & 1) -> (X & 1) | 0 -> X & 1
%a = and i32 %x, 1
%b = or i32 %a, 2
%c = and i32 %b, 1
ret i32 %c
; CHECK: ret i32 %a
}