diff options
| -rw-r--r-- | lib/Transforms/Scalar/GVN.cpp | 40 | ||||
| -rw-r--r-- | test/Transforms/GVN/condprop.ll | 19 |
2 files changed, 9 insertions, 50 deletions
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp index 03ebbb1512..70012524dc 100644 --- a/lib/Transforms/Scalar/GVN.cpp +++ b/lib/Transforms/Scalar/GVN.cpp @@ -1994,37 +1994,15 @@ bool GVN::propagateEquality(Value *LHS, Value *RHS, BasicBlock *Root) { /// particular 'Dst' must not be reachable via another edge from 'Src'. static bool isOnlyReachableViaThisEdge(BasicBlock *Src, BasicBlock *Dst, DominatorTree *DT) { - // First off, there must not be more than one edge from Src to Dst, there - // should be exactly one. So keep track of the number of times Src occurs - // as a predecessor of Dst and fail if it's more than once. - bool SawEdgeFromSrc = false; - for (pred_iterator PI = pred_begin(Dst), PE = pred_end(Dst); PI != PE; ++PI) { - if (*PI != Src) - continue; - // An edge from Src to Dst. - if (SawEdgeFromSrc) - // There are multiple edges from Src to Dst - fail. - return false; - SawEdgeFromSrc = true; - } - assert(SawEdgeFromSrc && "No edge between these basic blocks!"); - - // Secondly, any other predecessors of Dst should be dominated by Dst. If the - // predecessor is not dominated by Dst, then it must be possible to reach it - // either without passing through Src (thus not via the edge) or by passing - // through Src but taking a different edge out of Src. Either way Dst can be - // reached without passing via the edge, so fail. - for (pred_iterator PI = pred_begin(Dst), PE = pred_end(Dst); PI != PE; ++PI) { - BasicBlock *Pred = *PI; - if (Pred != Src && !DT->dominates(Dst, Pred)) - return false; - } - - // Every path from the entry block to Dst must at some point pass to Dst from - // a predecessor that is not dominated by Dst. This predecessor can only be - // Src, since all others are dominated by Dst. As there is only one edge from - // Src to Dst, the path passes by this edge. - return true; + // While in theory it is interesting to consider the case in which Dst has + // more than one predecessor, because Dst might be part of a loop which is + // only reachable from Src, in practice it is pointless since at the time + // GVN runs all such loops have preheaders, which means that Dst will have + // been changed to have only one predecessor, namely Src. + pred_iterator PI = pred_begin(Dst), PE = pred_end(Dst); + assert(PI != PE && *PI == Src && "No edge between these basic blocks!"); + (void)Src; + return PE == ++PI; } /// processInstruction - When calculating availability, handle an instruction diff --git a/test/Transforms/GVN/condprop.ll b/test/Transforms/GVN/condprop.ll index 0b31b01b7b..c17c994011 100644 --- a/test/Transforms/GVN/condprop.ll +++ b/test/Transforms/GVN/condprop.ll @@ -55,25 +55,6 @@ return: ; preds = %bb8 } declare void @foo(i1) - -; CHECK: @test2 -define void @test2(i1 %x, i1 %y) { - %z = or i1 %x, %y - br i1 %z, label %true, label %false -true: -; CHECK: true: - %z2 = or i1 %x, %y - call void @foo(i1 %z2) -; CHECK: call void @foo(i1 true) - br label %true -false: -; CHECK: false: - %z3 = or i1 %x, %y - call void @foo(i1 %z3) -; CHECK: call void @foo(i1 false) - br label %false -} - declare void @bar(i32) ; CHECK: @test3 |