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A better fix for PR2503 that doesn't pessimize GVN in the presence of unreachable blocks.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53032 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -19,7 +19,6 @@
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#include "llvm/Instructions.h"
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#include "llvm/Function.h"
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#include "llvm/Analysis/AliasAnalysis.h"
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#include "llvm/Analysis/Dominators.h"
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#include "llvm/Support/CFG.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Target/TargetData.h"
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@ -83,7 +82,6 @@ void MemoryDependenceAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesAll();
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AU.addRequiredTransitive<AliasAnalysis>();
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AU.addRequiredTransitive<TargetData>();
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AU.addRequiredTransitive<DominatorTree>();
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}
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/// getCallSiteDependency - Private helper for finding the local dependencies
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@ -224,17 +222,6 @@ void MemoryDependenceAnalysis::nonLocalHelper(Instruction* query,
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continue;
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}
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// Don't recur upwards if the current block is unreachable.
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// Instead, mark it as having no dependency on this path,
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// which will block optzns from occuring. For this reason,
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// eliminating unreachable blocks before running a memdep
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// based optimization is recommended.
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DominatorTree& DT = getAnalysis<DominatorTree>();
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if (!DT.isReachableFromEntry(BB)) {
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resp.insert(std::make_pair(BB, None));
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continue;
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}
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// If we didn't find anything, recurse on the precessors of this block
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// Only do this for blocks with a small number of predecessors.
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bool predOnStack = false;
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@ -808,6 +808,11 @@ Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,
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DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
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if (V != Phis.end() && !top_level) return V->second;
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if (!getAnalysis<DominatorTree>().isReachableFromEntry(BB)) {
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Phis[BB] = UndefValue::get(orig->getType());
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return UndefValue::get(orig->getType());
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}
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BasicBlock* singlePred = BB->getSinglePredecessor();
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if (singlePred) {
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Value *ret = GetValueForBlock(singlePred, orig, Phis);
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36
test/Transforms/GVN/2008-07-02-Unreachable.ll
Normal file
36
test/Transforms/GVN/2008-07-02-Unreachable.ll
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@ -0,0 +1,36 @@
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; RUN: llvm-as < %s | opt -gvn | llvm-dis | grep undef
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; PR2503
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target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
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target triple = "i686-apple-darwin9.3.0"
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@g_3 = external global i8 ; <i8*> [#uses=2]
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define i32 @func_1() nounwind {
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entry:
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br i1 false, label %ifelse, label %ifthen
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ifthen: ; preds = %entry
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br label %ifend
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ifelse: ; preds = %entry
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%tmp3 = load i8* @g_3 ; <i8> [#uses=0]
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br label %forcond.thread
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forcond.thread: ; preds = %ifelse
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br label %afterfor
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forcond: ; preds = %forinc
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br i1 false, label %afterfor, label %forbody
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forbody: ; preds = %forcond
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br label %forinc
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forinc: ; preds = %forbody
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br label %forcond
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afterfor: ; preds = %forcond, %forcond.thread
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%tmp10 = load i8* @g_3 ; <i8> [#uses=0]
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br label %ifend
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ifend: ; preds = %afterfor, %ifthen
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ret i32 0
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}
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