[llvm] r311039 - [ADCE][Dominators] Teach ADCE to preserve dominators
Jakub Kuderski via llvm-commits
llvm-commits at lists.llvm.org
Wed Aug 16 13:50:23 PDT 2017
Author: kuhar
Date: Wed Aug 16 13:50:23 2017
New Revision: 311039
URL: http://llvm.org/viewvc/llvm-project?rev=311039&view=rev
Log:
[ADCE][Dominators] Teach ADCE to preserve dominators
Summary:
This patch teaches ADCE to preserve both DominatorTrees and PostDominatorTrees.
I didn't notice any performance impact when bootstrapping clang with this patch.
Reviewers: dberlin, chandlerc, sanjoy, davide, grosser, brzycki
Reviewed By: davide
Subscribers: grandinj, zhendongsu, llvm-commits, david2050
Differential Revision: https://reviews.llvm.org/D35869
Added:
llvm/trunk/test/Transforms/ADCE/domtree-DoubleDeletion.ll
llvm/trunk/test/Transforms/ADCE/unreachable.ll
Modified:
llvm/trunk/include/llvm/Support/GenericDomTreeConstruction.h
llvm/trunk/lib/Transforms/Scalar/ADCE.cpp
Modified: llvm/trunk/include/llvm/Support/GenericDomTreeConstruction.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/GenericDomTreeConstruction.h?rev=311039&r1=311038&r2=311039&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Support/GenericDomTreeConstruction.h (original)
+++ llvm/trunk/include/llvm/Support/GenericDomTreeConstruction.h Wed Aug 16 13:50:23 2017
@@ -914,7 +914,12 @@ struct SemiNCAInfo {
if (!FromTN) return;
const TreeNodePtr ToTN = DT.getNode(To);
- assert(ToTN && "To already unreachable -- there is no edge to delete");
+ if (!ToTN) {
+ DEBUG(dbgs() << "\tTo (" << BlockNamePrinter(To)
+ << ") already unreachable -- there is no edge to delete\n");
+ return;
+ }
+
const NodePtr NCDBlock = DT.findNearestCommonDominator(From, To);
const TreeNodePtr NCD = DT.getNode(NCDBlock);
Modified: llvm/trunk/lib/Transforms/Scalar/ADCE.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/ADCE.cpp?rev=311039&r1=311038&r2=311039&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/ADCE.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/ADCE.cpp Wed Aug 16 13:50:23 2017
@@ -27,6 +27,7 @@
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/DebugInfoMetadata.h"
+#include "llvm/IR/Dominators.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/Instructions.h"
@@ -89,6 +90,10 @@ struct BlockInfoType {
class AggressiveDeadCodeElimination {
Function &F;
+
+ // ADCE does not use DominatorTree per se, but it updates it to preserve the
+ // analysis.
+ DominatorTree &DT;
PostDominatorTree &PDT;
/// Mapping of blocks to associated information, an element in BlockInfoVec.
@@ -157,9 +162,10 @@ class AggressiveDeadCodeElimination {
void makeUnconditional(BasicBlock *BB, BasicBlock *Target);
public:
- AggressiveDeadCodeElimination(Function &F, PostDominatorTree &PDT)
- : F(F), PDT(PDT) {}
- bool performDeadCodeElimination();
+ AggressiveDeadCodeElimination(Function &F, DominatorTree &DT,
+ PostDominatorTree &PDT)
+ : F(F), DT(DT), PDT(PDT) {}
+ bool performDeadCodeElimination();
};
}
@@ -557,14 +563,31 @@ void AggressiveDeadCodeElimination::upda
}
assert((PreferredSucc && PreferredSucc->PostOrder > 0) &&
"Failed to find safe successor for dead branch");
+
+ // Collect removed successors to update the (Post)DominatorTrees.
+ SmallPtrSet<BasicBlock *, 4> RemovedSuccessors;
bool First = true;
for (auto *Succ : successors(BB)) {
- if (!First || Succ != PreferredSucc->BB)
+ if (!First || Succ != PreferredSucc->BB) {
Succ->removePredecessor(BB);
- else
+ RemovedSuccessors.insert(Succ);
+ } else
First = false;
}
makeUnconditional(BB, PreferredSucc->BB);
+
+ // Inform the dominators about the deleted CFG edges.
+ for (auto *Succ : RemovedSuccessors) {
+ // It might have happened that the same successor appeared multiple times
+ // and the CFG edge wasn't really removed.
+ if (Succ != PreferredSucc->BB) {
+ DEBUG(dbgs() << "ADCE: Removing (Post)DomTree edge " << BB->getName()
+ << " -> " << Succ->getName() << "\n");
+ DT.deleteEdge(BB, Succ);
+ PDT.deleteEdge(BB, Succ);
+ }
+ }
+
NumBranchesRemoved += 1;
}
}
@@ -609,6 +632,9 @@ void AggressiveDeadCodeElimination::make
InstInfo[NewTerm].Live = true;
if (const DILocation *DL = PredTerm->getDebugLoc())
NewTerm->setDebugLoc(DL);
+
+ InstInfo.erase(PredTerm);
+ PredTerm->eraseFromParent();
}
//===----------------------------------------------------------------------===//
@@ -617,13 +643,16 @@ void AggressiveDeadCodeElimination::make
//
//===----------------------------------------------------------------------===//
PreservedAnalyses ADCEPass::run(Function &F, FunctionAnalysisManager &FAM) {
+ auto &DT = FAM.getResult<DominatorTreeAnalysis>(F);
auto &PDT = FAM.getResult<PostDominatorTreeAnalysis>(F);
- if (!AggressiveDeadCodeElimination(F, PDT).performDeadCodeElimination())
+ if (!AggressiveDeadCodeElimination(F, DT, PDT).performDeadCodeElimination())
return PreservedAnalyses::all();
PreservedAnalyses PA;
PA.preserveSet<CFGAnalyses>();
PA.preserve<GlobalsAA>();
+ PA.preserve<DominatorTreeAnalysis>();
+ PA.preserve<PostDominatorTreeAnalysis>();
return PA;
}
@@ -637,15 +666,22 @@ struct ADCELegacyPass : public FunctionP
bool runOnFunction(Function &F) override {
if (skipFunction(F))
return false;
+
+ auto &DT = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
auto &PDT = getAnalysis<PostDominatorTreeWrapperPass>().getPostDomTree();
- return AggressiveDeadCodeElimination(F, PDT).performDeadCodeElimination();
+ return AggressiveDeadCodeElimination(F, DT, PDT)
+ .performDeadCodeElimination();
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
+ // We require DominatorTree here only to update and thus preserve it.
+ AU.addRequired<DominatorTreeWrapperPass>();
AU.addRequired<PostDominatorTreeWrapperPass>();
if (!RemoveControlFlowFlag)
AU.setPreservesCFG();
AU.addPreserved<GlobalsAAWrapperPass>();
+ AU.addPreserved<DominatorTreeWrapperPass>();
+ AU.addPreserved<PostDominatorTreeWrapperPass>();
}
};
}
Added: llvm/trunk/test/Transforms/ADCE/domtree-DoubleDeletion.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/ADCE/domtree-DoubleDeletion.ll?rev=311039&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/ADCE/domtree-DoubleDeletion.ll (added)
+++ llvm/trunk/test/Transforms/ADCE/domtree-DoubleDeletion.ll Wed Aug 16 13:50:23 2017
@@ -0,0 +1,39 @@
+; RUN: opt < %s -gvn -simplifycfg -adce | llvm-dis
+; RUN: opt < %s -gvn -simplifycfg -adce -verify-dom-info | llvm-dis
+
+; This test makes sure that the DominatorTree properly handles
+; deletion of edges that go to forward-unreachable regions.
+; In this case, %land.end is already forward unreachable when
+; the DT gets informed about the deletion of %entry -> %land.end.
+
+ at a = common global i32 0, align 4
+
+define i32 @main() {
+entry:
+ %retval = alloca i32, align 4
+ store i32 0, i32* %retval, align 4
+ %0 = load i32, i32* @a, align 4
+ %cmp = icmp ne i32 %0, 1
+ br i1 %cmp, label %land.rhs, label %land.end4
+
+land.rhs: ; preds = %entry
+ %1 = load i32, i32* @a, align 4
+ %tobool = icmp ne i32 %1, 0
+ br i1 %tobool, label %land.rhs1, label %land.end
+
+land.rhs1: ; preds = %land.rhs
+ br label %land.end
+
+land.end: ; preds = %land.rhs1, %land.rhs
+ %2 = phi i1 [ false, %land.rhs ], [ true, %land.rhs1 ]
+ %land.ext = zext i1 %2 to i32
+ %conv = trunc i32 %land.ext to i16
+ %conv2 = sext i16 %conv to i32
+ %tobool3 = icmp ne i32 %conv2, 0
+ br label %land.end4
+
+land.end4: ; preds = %land.end, %entry
+ %3 = phi i1 [ false, %entry ], [ %tobool3, %land.end ]
+ %land.ext5 = zext i1 %3 to i32
+ ret i32 0
+}
Added: llvm/trunk/test/Transforms/ADCE/unreachable.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/ADCE/unreachable.ll?rev=311039&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/ADCE/unreachable.ll (added)
+++ llvm/trunk/test/Transforms/ADCE/unreachable.ll Wed Aug 16 13:50:23 2017
@@ -0,0 +1,18 @@
+; RUN: opt < %s -adce -simplifycfg | llvm-dis
+; RUN: opt < %s -passes=adce | llvm-dis
+
+define i32 @Test(i32 %A, i32 %B) {
+BB1:
+ br label %BB4
+
+BB2: ; No predecessors!
+ br label %BB3
+
+BB3: ; preds = %BB4, %BB2
+ %ret = phi i32 [ %X, %BB4 ], [ %B, %BB2 ] ; <i32> [#uses=1]
+ ret i32 %ret
+
+BB4: ; preds = %BB1
+ %X = phi i32 [ %A, %BB1 ] ; <i32> [#uses=1]
+ br label %BB3
+}
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