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Add generic simplification of associative operations, generalizing

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a couple of existing transforms.  This fires surprisingly often, for
example when compiling gcc "(X+(-1))+1->X" fires quite a lot as well
as various "and" simplifications (usually with a phi node operand).
Most of the time this doesn't make a real difference since the same
thing would have been done elsewhere anyway, eg: by instcombine, but
there are a few places where this results in simplifications that we
were not doing before.

llvm-svn: 122326
This commit is contained in:
Duncan Sands 2010-12-21 08:49:00 +00:00
parent 0243f1d21e
commit 5880f299da
3 changed files with 185 additions and 28 deletions
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146
lib/Analysis/InstructionSimplify.cpp
View File

@ -53,6 +53,100 @@ 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.
static Value *SimplifyAssociativeBinOp(unsigned Opcode, Value *LHS, Value *RHS,
const TargetData *TD,
const DominatorTree *DT,
unsigned MaxRecurse) {
assert(Instruction::isAssociative(Opcode) && "Not an associative operation!");
// 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);
// Transform: "(A op B) op C" ==> "A op (B op C)" if it simplifies completely.
if (Op0 && Op0->getOpcode() == Opcode) {
Value *A = Op0->getOperand(0);
Value *B = Op0->getOperand(1);
Value *C = RHS;
// Does "B op C" simplify?
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;
// Otherwise return "A op V" if it simplifies.
if (Value *W = SimplifyBinOp(Opcode, A, V, TD, DT, MaxRecurse))
return W;
}
}
// Transform: "A op (B op C)" ==> "(A op B) op C" if it simplifies completely.
if (Op1 && Op1->getOpcode() == Opcode) {
Value *A = LHS;
Value *B = Op1->getOperand(0);
Value *C = Op1->getOperand(1);
// Does "A op B" simplify?
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;
// Otherwise return "V op C" if it simplifies.
if (Value *W = SimplifyBinOp(Opcode, V, C, TD, DT, MaxRecurse))
return W;
}
}
// The remaining transforms require commutativity as well as associativity.
if (!Instruction::isCommutative(Opcode))
return 0;
// Transform: "(A op B) op C" ==> "(C op A) op B" if it simplifies completely.
if (Op0 && Op0->getOpcode() == Opcode) {
Value *A = Op0->getOperand(0);
Value *B = Op0->getOperand(1);
Value *C = RHS;
// Does "C op A" simplify?
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;
// Otherwise return "V op B" if it simplifies.
if (Value *W = SimplifyBinOp(Opcode, V, B, TD, DT, MaxRecurse))
return W;
}
}
// Transform: "A op (B op C)" ==> "B op (C op A)" if it simplifies completely.
if (Op1 && Op1->getOpcode() == Opcode) {
Value *A = LHS;
Value *B = Op1->getOperand(0);
Value *C = Op1->getOperand(1);
// Does "C op A" simplify?
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;
// Otherwise return "B op V" if it simplifies.
if (Value *W = SimplifyBinOp(Opcode, B, V, TD, DT, MaxRecurse))
return W;
}
}
return 0;
}
/// 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.
@ -266,6 +360,11 @@ static Value *SimplifyAddInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
match(Op1, m_Not(m_Specific(Op0))))
return Constant::getAllOnesValue(Op0->getType());
// Try some generic simplifications for associative operations.
if (Value *V = SimplifyAssociativeBinOp(Instruction::Add, Op0, Op1, 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
@ -379,15 +478,10 @@ static Value *SimplifyAndInst(Value *Op0, Value *Op1, const TargetData *TD,
(A == Op0 || B == Op0))
return Op0;
// (A & B) & A -> A & B
if (match(Op0, m_And(m_Value(A), m_Value(B))) &&
(A == Op1 || B == Op1))
return Op0;
// A & (A & B) -> A & B
if (match(Op1, m_And(m_Value(A), m_Value(B))) &&
(A == Op0 || B == Op0))
return Op1;
// Try some generic simplifications for associative operations.
if (Value *V = SimplifyAssociativeBinOp(Instruction::And, Op0, Op1, 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.
@ -458,15 +552,10 @@ static Value *SimplifyOrInst(Value *Op0, Value *Op1, const TargetData *TD,
(A == Op0 || B == Op0))
return Op0;
// (A | B) | A -> A | B
if (match(Op0, m_Or(m_Value(A), m_Value(B))) &&
(A == Op1 || B == Op1))
return Op0;
// A | (A | B) -> A | B
if (match(Op1, m_Or(m_Value(A), m_Value(B))) &&
(A == Op0 || B == Op0))
return Op1;
// Try some generic simplifications for associative operations.
if (Value *V = SimplifyAssociativeBinOp(Instruction::Or, Op0, Op1, 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.
@ -518,20 +607,15 @@ static Value *SimplifyXorInst(Value *Op0, Value *Op1, const TargetData *TD,
return Constant::getNullValue(Op0->getType());
// A ^ ~A = ~A ^ A = -1
Value *A = 0, *B = 0;
Value *A = 0;
if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
(match(Op1, m_Not(m_Value(A))) && A == Op0))
return Constant::getAllOnesValue(Op0->getType());
// (A ^ B) ^ A = B
if (match(Op0, m_Xor(m_Value(A), m_Value(B))) &&
(A == Op1 || B == Op1))
return A == Op1 ? B : A;
// A ^ (A ^ B) = B
if (match(Op1, m_Xor(m_Value(A), m_Value(B))) &&
(A == Op0 || B == Op0))
return A == Op0 ? B : A;
// Try some generic simplifications for associative operations.
if (Value *V = SimplifyAssociativeBinOp(Instruction::Xor, Op0, Op1, 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
@ -855,6 +939,12 @@ static Value *SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS,
return ConstantFoldInstOperands(Opcode, LHS->getType(), COps, 2, TD);
}
// If the operation is associative, try some generic simplifications.
if (Instruction::isAssociative(Opcode))
if (Value *V = SimplifyAssociativeBinOp(Opcode, LHS, RHS, 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 (MaxRecurse && (isa<SelectInst>(LHS) || isa<SelectInst>(RHS)))

64
test/Transforms/InstSimplify/2010-12-20-Reassociate.ll Normal file
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@ -0,0 +1,64 @@
; RUN: opt < %s -instsimplify -S | FileCheck %s
define i32 @add1(i32 %x) {
; CHECK: @add1
; (X + -1) + 1 -> X
%l = add i32 %x, -1
%r = add i32 %l, 1
ret i32 %r
; CHECK: ret i32 %x
}
define i32 @and1(i32 %x, i32 %y) {
; CHECK: @and1
; (X & Y) & X -> X & Y
%l = and i32 %x, %y
%r = and i32 %l, %x
ret i32 %r
; CHECK: ret i32 %l
}
define i32 @and2(i32 %x, i32 %y) {
; CHECK: @and2
; X & (X & Y) -> X & Y
%r = and i32 %x, %y
%l = and i32 %x, %r
ret i32 %l
; CHECK: ret i32 %r
}
define i32 @or1(i32 %x, i32 %y) {
; CHECK: @or1
; (X | Y) | X -> X | Y
%l = or i32 %x, %y
%r = or i32 %l, %x
ret i32 %r
; CHECK: ret i32 %l
}
define i32 @or2(i32 %x, i32 %y) {
; CHECK: @or2
; X | (X | Y) -> X | Y
%r = or i32 %x, %y
%l = or i32 %x, %r
ret i32 %l
; CHECK: ret i32 %r
}
define i32 @xor1(i32 %x, i32 %y) {
; CHECK: @xor1
; (X ^ Y) ^ X = Y
%l = xor i32 %x, %y
%r = xor i32 %l, %x
ret i32 %r
; CHECK: ret i32 %y
}
define i32 @xor2(i32 %x, i32 %y) {
; CHECK: @xor2
; X ^ (X ^ Y) = Y
%r = xor i32 %x, %y
%l = xor i32 %x, %r
ret i32 %l
; CHECK: ret i32 %y
}

3
test/Transforms/InstSimplify/dg.exp Normal file
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@ -0,0 +1,3 @@
load_lib llvm.exp
RunLLVMTests [lsort [glob -nocomplain $srcdir/$subdir/*.{ll,c,cpp}]]