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Fold (-x + -y) -> -(x+y) which promotes better association, fixing

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the second half of PR2047


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47244 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2008-02-17 21:03:36 +00:00
parent 5329bb22e9
commit dd12f96c5e
2 changed files with 22 additions and 2 deletions
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12
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -2090,8 +2090,16 @@ Instruction *InstCombiner::visitAdd(BinaryOperator &I) {
}
// -A + B --> B - A
if (Value *V = dyn_castNegVal(LHS))
return BinaryOperator::createSub(RHS, V);
// -A + -B --> -(A + B)
if (Value *LHSV = dyn_castNegVal(LHS)) {
if (Value *RHSV = dyn_castNegVal(RHS)) {
Instruction *NewAdd = BinaryOperator::createAdd(LHSV, RHSV, "sum");
InsertNewInstBefore(NewAdd, I);
return BinaryOperator::createNeg(NewAdd);
}
return BinaryOperator::createSub(RHS, LHSV);
}
// A + -B --> A - B
if (!isa<Constant>(RHS))

12
test/Transforms/InstCombine/addnegneg.ll Normal file
View File

@ -0,0 +1,12 @@
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep { sub } | count 1
; PR2047
define i32 @l(i32 %a, i32 %b, i32 %c, i32 %d) {
entry:
%b.neg = sub i32 0, %b ; <i32> [#uses=1]
%c.neg = sub i32 0, %c ; <i32> [#uses=1]
%sub4 = add i32 %c.neg, %b.neg ; <i32> [#uses=1]
%sub6 = add i32 %sub4, %d ; <i32> [#uses=1]
ret i32 %sub6
}