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Fix for pr24866 

Turns out that not every basic block is guaranteed to have a node within the DominatorTree.  This is really hard to trigger, but the test case from the PR managed to do so.  There's active discussion continuing about what documentation and/or invariants needed cleaned up.

llvm-svn: 248216
This commit is contained in:
Philip Reames 2015-09-21 22:04:10 +00:00
parent 4ea00210f2
commit 963febd4f8
2 changed files with 52 additions and 1 deletions
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9
llvm/lib/Analysis/ValueTracking.cpp
View File

@ -609,6 +609,11 @@ static void computeKnownBitsFromDominatingCondition(Value *V, APInt &KnownZero,
if (!Q.DT || !Q.CxtI)
return;
Instruction *Cxt = const_cast<Instruction *>(Q.CxtI);
// The context instruction might be in a statically unreachable block. If
// so, asking dominator queries may yield suprising results. (e.g. the block
// may not have a dom tree node)
if (!Q.DT->isReachableFromEntry(Cxt->getParent()))
return;
// Avoid useless work
if (auto VI = dyn_cast<Instruction>(V))
@ -655,7 +660,9 @@ static void computeKnownBitsFromDominatingCondition(Value *V, APInt &KnownZero,
// instruction. Finding a condition where one path dominates the context
// isn't enough because both the true and false cases could merge before
// the context instruction we're actually interested in. Instead, we need
// to ensure that the taken *edge* dominates the context instruction.
// to ensure that the taken *edge* dominates the context instruction. We
// know that the edge must be reachable since we started from a reachable
// block.
BasicBlock *BB0 = BI->getSuccessor(0);
BasicBlockEdge Edge(BI->getParent(), BB0);
if (!Edge.isSingleEdge() || !Q.DT->dominates(Edge, Q.CxtI->getParent()))

44
llvm/test/Analysis/ValueTracking/pr24866.ll Normal file
View File

@ -0,0 +1,44 @@
; RUN: opt -S %s -value-tracking-dom-conditions -licm -load-combine | FileCheck %s
; In pr24866.ll, we saw a crash when accessing a nullptr returned when
; asking for a dominator tree Node. This reproducer is really fragile,
; but it's currently the best we have.
%struct.c_derived_tbl.2.5.8.11.14.17.23.38.59.80.92.98.104.107.155.183 = type { [256 x i32], [256 x i8] }
; Function Attrs: nounwind uwtable
define void @encode_one_blockX2(%struct.c_derived_tbl.2.5.8.11.14.17.23.38.59.80.92.98.104.107.155.183* nocapture readonly %actbl) #0 {
; CHECK-LABEL: @encode_one_blockX2
entry:
br i1 false, label %L_KLOOP_01, label %L_KLOOP.preheader
L_KLOOP_01: ; preds = %while.end, %entry
br label %L_KLOOP.preheader
L_KLOOP_08: ; preds = %while.end
br label %L_KLOOP.preheader
L_KLOOP.preheader: ; preds = %L_KLOOP_08, %L_KLOOP_01, %entry
%r.2.ph = phi i32 [ undef, %L_KLOOP_08 ], [ 0, %entry ], [ undef, %L_KLOOP_01 ]
br label %L_KLOOP
L_KLOOP: ; preds = %while.end, %L_KLOOP.preheader
%r.2 = phi i32 [ 0, %while.end ], [ %r.2.ph, %L_KLOOP.preheader ]
br i1 true, label %while.body, label %while.end
while.body: ; preds = %while.body, %L_KLOOP
br label %while.body
while.end: ; preds = %L_KLOOP
%shl105 = shl i32 %r.2, 4
%add106 = add nsw i32 %shl105, undef
%idxprom107 = sext i32 %add106 to i64
%arrayidx108 = getelementptr inbounds %struct.c_derived_tbl.2.5.8.11.14.17.23.38.59.80.92.98.104.107.155.183, %struct.c_derived_tbl.2.5.8.11.14.17.23.38.59.80.92.98.104.107.155.183* %actbl, i64 0, i32 0, i64 %idxprom107
%0 = load i32, i32* %arrayidx108, align 4
%arrayidx110 = getelementptr inbounds %struct.c_derived_tbl.2.5.8.11.14.17.23.38.59.80.92.98.104.107.155.183, %struct.c_derived_tbl.2.5.8.11.14.17.23.38.59.80.92.98.104.107.155.183* %actbl, i64 0, i32 1, i64 %idxprom107
%1 = load i8, i8* %arrayidx110, align 1
indirectbr i8* undef, [label %L_KLOOP_DONE, label %L_KLOOP_01, label %L_KLOOP_08, label %L_KLOOP]
L_KLOOP_DONE: ; preds = %while.end
ret void
}