diff options
| author | Paul Redmond <paul.redmond@intel.com> | 2013-02-12 15:21:21 +0000 |
|---|---|---|
| committer | Paul Redmond <paul.redmond@intel.com> | 2013-02-12 15:21:21 +0000 |
| commit | 5c97450df748819381daa4c4d400c39b0d7378ae (patch) | |
| tree | 248ac9d6c584c8abdf1caaab94aba84ca3d24715 /lib/CodeGen/SelectionDAG/DAGCombiner.cpp | |
| parent | 7eacad03efda36e09ebd96e95d7891cadaaa9087 (diff) | |
PR14562 - Truncation of left shift became undef
DAGCombiner::ReduceLoadWidth was converting (trunc i32 (shl i64 v, 32))
into (shl i32 v, 32) into undef. To prevent this, check the shift count
against the final result size.
Patch by: Kevin Schoedel
Reviewed by: Nadav Rotem
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174972 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/CodeGen/SelectionDAG/DAGCombiner.cpp')
| -rw-r--r-- | lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 11 |
1 files changed, 9 insertions, 2 deletions
diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp index 5b83149982..67fa39d9c2 100644 --- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp +++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp @@ -5163,8 +5163,15 @@ SDValue DAGCombiner::ReduceLoadWidth(SDNode *N) { EVT ShImmTy = getShiftAmountTy(Result.getValueType()); if (!isUIntN(ShImmTy.getSizeInBits(), ShLeftAmt)) ShImmTy = VT; - Result = DAG.getNode(ISD::SHL, N0.getDebugLoc(), VT, - Result, DAG.getConstant(ShLeftAmt, ShImmTy)); + // If the shift amount is as large as the result size (but, presumably, + // no larger than the source) then the useful bits of the result are + // zero; we can't simply return the shortened shift, because the result + // of that operation is undefined. + if (ShLeftAmt >= VT.getSizeInBits()) + Result = DAG.getConstant(0, VT); + else + Result = DAG.getNode(ISD::SHL, N0.getDebugLoc(), VT, + Result, DAG.getConstant(ShLeftAmt, ShImmTy)); } // Return the new loaded value. |