forked from OSchip/llvm-project
Memory Dependence Analysis: fix a miscompile that uses DT to approxmiate the
reachablity. We conservatively approximate the reachability analysis by saying it is not reachable if there is a single path starting from "From" and the path does not reach "To". rdar://12801584 llvm-svn: 171512
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@ -361,8 +361,28 @@ AliasAnalysis::getModRefInfo(const AtomicRMWInst *RMW, const Location &Loc) {
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}
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namespace {
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// Conservatively return true. Return false, if there is a single path
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// starting from "From" and the path does not reach "To".
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static bool hasPath(const BasicBlock *From, const BasicBlock *To) {
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const unsigned MaxCheck = 5;
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const BasicBlock *Current = From;
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for (unsigned I = 0; I < MaxCheck; I++) {
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unsigned NumSuccs = Current->getTerminator()->getNumSuccessors();
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if (NumSuccs > 1)
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return true;
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if (NumSuccs == 0)
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return false;
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Current = Current->getTerminator()->getSuccessor(0);
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if (Current == To)
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return true;
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}
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return true;
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}
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/// Only find pointer captures which happen before the given instruction. Uses
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/// the dominator tree to determine whether one instruction is before another.
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/// Only support the case where the Value is defined in the same basic block
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/// as the given instruction and the use.
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struct CapturesBefore : public CaptureTracker {
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CapturesBefore(const Instruction *I, DominatorTree *DT)
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: BeforeHere(I), DT(DT), Captured(false) {}
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@ -372,8 +392,15 @@ namespace {
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bool shouldExplore(Use *U) {
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Instruction *I = cast<Instruction>(U->getUser());
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BasicBlock *BB = I->getParent();
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if (BeforeHere != I &&
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(!DT->isReachableFromEntry(BB) || DT->dominates(BeforeHere, I)))
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// We explore this usage only if the usage can reach "BeforeHere".
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// If use is not reachable from entry, there is no need to explore.
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if (BeforeHere != I && !DT->isReachableFromEntry(BB))
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return false;
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// If the value is defined in the same basic block as use and BeforeHere,
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// there is no need to explore the use if BeforeHere dominates use.
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// Check whether there is a path from I to BeforeHere.
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if (BeforeHere != I && DT->dominates(BeforeHere, I) &&
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!hasPath(BB, BeforeHere->getParent()))
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return false;
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return true;
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}
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@ -381,8 +408,11 @@ namespace {
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bool captured(Use *U) {
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Instruction *I = cast<Instruction>(U->getUser());
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BasicBlock *BB = I->getParent();
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if (BeforeHere != I &&
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(!DT->isReachableFromEntry(BB) || DT->dominates(BeforeHere, I)))
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// Same logic as in shouldExplore.
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if (BeforeHere != I && !DT->isReachableFromEntry(BB))
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return false;
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if (BeforeHere != I && DT->dominates(BeforeHere, I) &&
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!hasPath(BB, BeforeHere->getParent()))
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return false;
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Captured = true;
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return true;
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@ -0,0 +1,54 @@
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; RUN: opt < %s -basicaa -gvn -S | FileCheck %s
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target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
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target triple = "x86_64-apple-macosx10.7.0"
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; rdar://12801584
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; Value of %shouldExit can be changed by RunInMode.
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; Make sure we do not replace load %shouldExit in while.cond.backedge
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; with a phi node where the value from while.body is 0.
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define i32 @test() nounwind ssp {
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entry:
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; CHECK: test()
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; CHECK: while.body:
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; CHECK: call void @RunInMode
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; CHECK: br i1 %tobool, label %while.cond.backedge, label %if.then
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; CHECK: while.cond.backedge:
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; CHECK: load i32* %shouldExit
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; CHECK: br i1 %cmp, label %while.body
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%shouldExit = alloca i32, align 4
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%tasksIdle = alloca i32, align 4
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store i32 0, i32* %shouldExit, align 4
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store i32 0, i32* %tasksIdle, align 4
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call void @CTestInitialize(i32* %tasksIdle) nounwind
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%0 = load i32* %shouldExit, align 4
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%cmp1 = icmp eq i32 %0, 0
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br i1 %cmp1, label %while.body.lr.ph, label %while.end
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while.body.lr.ph:
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br label %while.body
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while.body:
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call void @RunInMode(i32 100) nounwind
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%1 = load i32* %tasksIdle, align 4
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%tobool = icmp eq i32 %1, 0
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br i1 %tobool, label %while.cond.backedge, label %if.then
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if.then:
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store i32 0, i32* %tasksIdle, align 4
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call void @TimerCreate(i32* %shouldExit) nounwind
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br label %while.cond.backedge
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while.cond.backedge:
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%2 = load i32* %shouldExit, align 4
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%cmp = icmp eq i32 %2, 0
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br i1 %cmp, label %while.body, label %while.cond.while.end_crit_edge
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while.cond.while.end_crit_edge:
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br label %while.end
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while.end:
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ret i32 0
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}
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declare void @CTestInitialize(i32*)
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declare void @RunInMode(i32)
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declare void @TimerCreate(i32*)
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