From be6a9a151adb3e9b47f45a10d31f451fd461720f Mon Sep 17 00:00:00 2001 From: Torok Edwin Date: Sat, 23 May 2009 17:29:48 +0000 Subject: Fix PR4254. The DAGCombiner created a negative shiftamount, stored in an unsigned variable. Later the optimizer eliminated the shift entirely as being undefined. Example: (srl (shl X, 56) 48). ShiftAmt is 4294967288. Fix it by checking that the shiftamount is positive, and storing in a signed variable. llvm-svn: 72331 --- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'llvm/lib/CodeGen') diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp index 6e0cc9f60a2..a866cb5629e 100644 --- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp +++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp @@ -2546,13 +2546,13 @@ SDValue DAGCombiner::visitSRA(SDNode *N) { MVT TruncVT = MVT::getIntegerVT(VTValSize - N1C->getZExtValue()); // Determine the residual right-shift amount. - unsigned ShiftAmt = N1C->getZExtValue() - N01C->getZExtValue(); + signed ShiftAmt = N1C->getZExtValue() - N01C->getZExtValue(); // If the shift is not a no-op (in which case this should be just a sign // extend already), the truncated to type is legal, sign_extend is legal // on that type, and the the truncate to that type is both legal and free, // perform the transform. - if (ShiftAmt && + if ((ShiftAmt > 0) && TLI.isOperationLegalOrCustom(ISD::SIGN_EXTEND, TruncVT) && TLI.isOperationLegalOrCustom(ISD::TRUNCATE, VT) && TLI.isTruncateFree(VT, TruncVT)) { -- cgit v1.2.3