[llvm-commits] [llvm] r69102 - in /llvm/trunk: lib/Transforms/Scalar/CondPropagate.cpp test/Transforms/CondProp/phisimplify3.ll
Chris Lattner
clattner at apple.com
Tue Apr 14 17:14:35 PDT 2009
On Apr 14, 2009, at 4:40 PM, Evan Cheng wrote:
> Author: evancheng
> Date: Tue Apr 14 18:40:03 2009
> New Revision: 69102
>
> URL: http://llvm.org/viewvc/llvm-project?rev=69102&view=rev
> Log:
> Optimize conditional branch on i1 phis with non-constant inputs.
>
> This turns:
>
> eq:
> %3 = icmp eq i32 %1, %2
> br label %join
>
> ne:
> %4 = icmp ne i32 %1, %2
> br label %join
>
> join:
> %5 = phi i1 [%3, %eq], [%4, %ne]
> br i1 %5, label %yes, label %no
Cool. I didn't scrutinize the code, but does this handle the case (or
avoid transforming) when "yes" or "no" have phi nodes? This will add
new preds, so phi nodes in them would need to be updated.
-Chris
>
>
> =>
>
> eq:
> %3 = icmp eq i32 %1, %2
> br i1 %3, label %yes, label %no
>
> ne:
> %4 = icmp ne i32 %1, %2
> br i1 %4, label %yes, label %no
>
> Added:
> llvm/trunk/test/Transforms/CondProp/phisimplify3.ll
> Modified:
> llvm/trunk/lib/Transforms/Scalar/CondPropagate.cpp
>
> Modified: llvm/trunk/lib/Transforms/Scalar/CondPropagate.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/CondPropagate.cpp?rev=69102&r1=69101&r2=69102&view=diff
>
> =
> =
> =
> =
> =
> =
> =
> =
> ======================================================================
> --- llvm/trunk/lib/Transforms/Scalar/CondPropagate.cpp (original)
> +++ llvm/trunk/lib/Transforms/Scalar/CondPropagate.cpp Tue Apr 14
> 18:40:03 2009
> @@ -51,6 +51,7 @@
> void SimplifyPredecessors(BranchInst *BI);
> void SimplifyPredecessors(SwitchInst *SI);
> void RevectorBlockTo(BasicBlock *FromBB, BasicBlock *ToBB);
> + bool RevectorBlockTo(BasicBlock *FromBB, Value *Cond,
> BranchInst *BI);
> };
> }
>
> @@ -160,20 +161,19 @@
> // Ok, we have this really simple case, walk the PHI operands,
> looking for
> // constants. Walk from the end to remove operands from the end
> when
> // possible, and to avoid invalidating "i".
> - for (unsigned i = PN->getNumIncomingValues(); i != 0; --i)
> - if (ConstantInt *CB = dyn_cast<ConstantInt>(PN-
> >getIncomingValue(i-1))) {
> - // If we have a constant, forward the edge from its current
> to its
> - // ultimate destination.
> - RevectorBlockTo(PN->getIncomingBlock(i-1),
> - BI->getSuccessor(CB->isZero()));
> - ++NumBrThread;
> -
> - // If there were two predecessors before this simplification,
> or if the
> - // PHI node contained all the same value except for the one
> we just
> - // substituted, the PHI node may be deleted. Don't iterate
> through it the
> - // last time.
> - if (BI->getCondition() != PN) return;
> - }
> + for (unsigned i = PN->getNumIncomingValues(); i != 0; --i) {
> + Value *InVal = PN->getIncomingValue(i-1);
> + if (!RevectorBlockTo(PN->getIncomingBlock(i-1), InVal, BI))
> + continue;
> +
> + ++NumBrThread;
> +
> + // If there were two predecessors before this simplification,
> or if the
> + // PHI node contained all the same value except for the one we
> just
> + // substituted, the PHI node may be deleted. Don't iterate
> through it the
> + // last time.
> + if (BI->getCondition() != PN) return;
> + }
> }
>
> // SimplifyPredecessors(switch) - We know that SI is switch based on
> a PHI node
> @@ -242,3 +242,44 @@
>
> MadeChange = true;
> }
> +
> +bool CondProp::RevectorBlockTo(BasicBlock *FromBB, Value *Cond,
> BranchInst *BI){
> + BranchInst *FromBr = cast<BranchInst>(FromBB->getTerminator());
> + if (!FromBr->isUnconditional())
> + return false;
> +
> + // Get the old block we are threading through.
> + BasicBlock *OldSucc = FromBr->getSuccessor(0);
> +
> + // If the condition is a constant, simply revector the
> unconditional branch at
> + // the end of FromBB to one of the successors of its current
> successor.
> + if (ConstantInt *CB = dyn_cast<ConstantInt>(Cond)) {
> + BasicBlock *ToBB = BI->getSuccessor(CB->isZero());
> +
> + // OldSucc had multiple successors. If ToBB has multiple
> predecessors, then
> + // the edge between them would be critical, which we already
> took care of.
> + // If ToBB has single operand PHI node then take care of it here.
> + FoldSingleEntryPHINodes(ToBB);
> +
> + // Update PHI nodes in OldSucc to know that FromBB no longer
> branches to it.
> + OldSucc->removePredecessor(FromBB);
> +
> + // Change FromBr to branch to the new destination.
> + FromBr->setSuccessor(0, ToBB);
> + } else {
> + // Insert the new conditional branch.
> + BranchInst::Create(BI->getSuccessor(0), BI->getSuccessor(1),
> Cond, FromBr);
> +
> + FoldSingleEntryPHINodes(BI->getSuccessor(0));
> + FoldSingleEntryPHINodes(BI->getSuccessor(1));
> +
> + // Update PHI nodes in OldSucc to know that FromBB no longer
> branches to it.
> + OldSucc->removePredecessor(FromBB);
> +
> + // Delete the old branch.
> + FromBr->eraseFromParent();
> + }
> +
> + MadeChange = true;
> + return true;
> +}
>
> Added: llvm/trunk/test/Transforms/CondProp/phisimplify3.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/CondProp/phisimplify3.ll?rev=69102&view=auto
>
> =
> =
> =
> =
> =
> =
> =
> =
> ======================================================================
> --- llvm/trunk/test/Transforms/CondProp/phisimplify3.ll (added)
> +++ llvm/trunk/test/Transforms/CondProp/phisimplify3.ll Tue Apr 14
> 18:40:03 2009
> @@ -0,0 +1,26 @@
> +; RUN: llvm-as < %s | opt -condprop | llvm-dis | not grep phi
> +
> +define i32 @foo(i1, i32, i32) {
> +prologue:
> + br i1 %0, label %eq, label %ne
> +
> +eq: ; preds = %prologue
> + store i32 0, i32* inttoptr (i32 10000 to i32*)
> + %3 = icmp eq i32 %1, %2 ; <i1> [#uses=1]
> + br label %join
> +
> +ne: ; preds = %prologue
> + %4 = icmp ne i32 %1, %2 ; <i1> [#uses=1]
> + br label %join
> +
> +join: ; preds = %ne, %eq
> + %5 = phi i1 [ %3, %eq ], [ %4, %ne ] ; <i1> [#uses=1]
> + br i1 %5, label %yes, label %no
> +
> +yes: ; preds = %join
> + store i32 0, i32* inttoptr (i32 20000 to i32*)
> + ret i32 5
> +
> +no: ; preds = %join
> + ret i32 20
> +}
>
>
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