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A better fix for PR2503 that doesn't pessimize GVN in the presence of unreachable blocks.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@53032 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Owen Anderson 2008-07-02 17:20:16 +00:00
parent bee98c66c0
commit f2aa160b35
3 changed files with 41 additions and 13 deletions
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13
lib/Analysis/MemoryDependenceAnalysis.cpp
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@ -19,7 +19,6 @@
#include "llvm/Instructions.h"
#include "llvm/Function.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/Dominators.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Target/TargetData.h"
@ -83,7 +82,6 @@ void MemoryDependenceAnalysis::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
AU.addRequiredTransitive<AliasAnalysis>();
AU.addRequiredTransitive<TargetData>();
AU.addRequiredTransitive<DominatorTree>();
}
/// getCallSiteDependency - Private helper for finding the local dependencies
@ -224,17 +222,6 @@ void MemoryDependenceAnalysis::nonLocalHelper(Instruction* query,
continue;
}
// Don't recur upwards if the current block is unreachable.
// Instead, mark it as having no dependency on this path,
// which will block optzns from occuring. For this reason,
// eliminating unreachable blocks before running a memdep
// based optimization is recommended.
DominatorTree& DT = getAnalysis<DominatorTree>();
if (!DT.isReachableFromEntry(BB)) {
resp.insert(std::make_pair(BB, None));
continue;
}
// If we didn't find anything, recurse on the precessors of this block
// Only do this for blocks with a small number of predecessors.
bool predOnStack = false;

5
lib/Transforms/Scalar/GVN.cpp
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@ -808,6 +808,11 @@ Value *GVN::GetValueForBlock(BasicBlock *BB, LoadInst* orig,
DenseMap<BasicBlock*, Value*>::iterator V = Phis.find(BB);
if (V != Phis.end() && !top_level) return V->second;
if (!getAnalysis<DominatorTree>().isReachableFromEntry(BB)) {
Phis[BB] = UndefValue::get(orig->getType());
return UndefValue::get(orig->getType());
}
BasicBlock* singlePred = BB->getSinglePredecessor();
if (singlePred) {
Value *ret = GetValueForBlock(singlePred, orig, Phis);

36
test/Transforms/GVN/2008-07-02-Unreachable.ll Normal file
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@ -0,0 +1,36 @@
; RUN: llvm-as < %s | opt -gvn | llvm-dis | grep undef
; PR2503
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"
target triple = "i686-apple-darwin9.3.0"
@g_3 = external global i8 ; <i8*> [#uses=2]
define i32 @func_1() nounwind {
entry:
br i1 false, label %ifelse, label %ifthen
ifthen: ; preds = %entry
br label %ifend
ifelse: ; preds = %entry
%tmp3 = load i8* @g_3 ; <i8> [#uses=0]
br label %forcond.thread
forcond.thread: ; preds = %ifelse
br label %afterfor
forcond: ; preds = %forinc
br i1 false, label %afterfor, label %forbody
forbody: ; preds = %forcond
br label %forinc
forinc: ; preds = %forbody
br label %forcond
afterfor: ; preds = %forcond, %forcond.thread
%tmp10 = load i8* @g_3 ; <i8> [#uses=0]
br label %ifend
ifend: ; preds = %afterfor, %ifthen
ret i32 0
}