reuse negates where possible instead of always creating them from scratch.
This allows us to optimize test12 into:
define i32 @test12(i32 %X) {
%factor = mul i32 %X, -3 ; <i32> [#uses=1]
%Z = add i32 %factor, 6 ; <i32> [#uses=1]
ret i32 %Z
}
instead of:
define i32 @test12(i32 %X) {
%Y = sub i32 6, %X ; <i32> [#uses=1]
%C = sub i32 %Y, %X ; <i32> [#uses=1]
%Z = sub i32 %C, %X ; <i32> [#uses=1]
ret i32 %Z
}
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92373 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Transforms/Scalar/Reassociate.cpp b/lib/Transforms/Scalar/Reassociate.cpp
index d22b9bf..bbb0e0a 100644
--- a/lib/Transforms/Scalar/Reassociate.cpp
+++ b/lib/Transforms/Scalar/Reassociate.cpp
@@ -376,6 +376,9 @@
// that should be processed next by the reassociation pass.
//
static Value *NegateValue(Value *V, Instruction *BI) {
+ if (Constant *C = dyn_cast<Constant>(V))
+ return ConstantExpr::getNeg(C);
+
// We are trying to expose opportunity for reassociation. One of the things
// that we want to do to achieve this is to push a negation as deep into an
// expression chain as possible, to expose the add instructions. In practice,
@@ -400,10 +403,36 @@
I->setName(I->getName()+".neg");
return I;
}
+
+ // Okay, we need to materialize a negated version of V with an instruction.
+ // Scan the use lists of V to see if we have one already.
+ for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;++UI){
+ if (!BinaryOperator::isNeg(*UI)) continue;
+
+ // We found one! Now we have to make sure that the definition dominates
+ // this use. We do this by moving it to the entry block (if it is a
+ // non-instruction value) or right after the definition. These negates will
+ // be zapped by reassociate later, so we don't need much finesse here.
+ BinaryOperator *TheNeg = cast<BinaryOperator>(*UI);
+
+ BasicBlock::iterator InsertPt;
+ if (Instruction *InstInput = dyn_cast<Instruction>(V)) {
+ if (InvokeInst *II = dyn_cast<InvokeInst>(InstInput)) {
+ InsertPt = II->getNormalDest()->begin();
+ } else {
+ InsertPt = InstInput;
+ ++InsertPt;
+ }
+ while (isa<PHINode>(InsertPt)) ++InsertPt;
+ } else {
+ InsertPt = TheNeg->getParent()->getParent()->getEntryBlock().begin();
+ }
+ TheNeg->moveBefore(InsertPt);
+ return TheNeg;
+ }
// Insert a 'neg' instruction that subtracts the value from zero to get the
// negation.
- //
return BinaryOperator::CreateNeg(V, V->getName() + ".neg", BI);
}