[llvm-commits] [llvm] r170505 - in /llvm/trunk: lib/CodeGen/SelectionDAG/TargetLowering.cpp test/CodeGen/Generic/dag-combine-crash.ll

[Nadav Rotem]

Author: nadav
Date: Wed Dec 19 01:39:08 2012
New Revision: 170505

URL: http://llvm.org/viewvc/llvm-project?rev=170505&view=rev
Log:
After reducing the size of an operation in the DAG we zero-extend the reduced
bitwidth op back to the original size. If we reduce ANDs then this can cause
an endless loop. This patch changes the ZEXT to ANY_EXTEND if the demanded bits
are equal or smaller than the size of the reduced operation.


Added:
    llvm/trunk/test/CodeGen/Generic/dag-combine-crash.ll
Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/TargetLowering.cpp

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/TargetLowering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/TargetLowering.cpp?rev=170505&r1=170504&r2=170505&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/TargetLowering.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/TargetLowering.cpp Wed Dec 19 01:39:08 2012
@@ -1161,7 +1161,8 @@
   // Search for the smallest integer type with free casts to and from
   // Op's type. For expedience, just check power-of-2 integer types.
   const TargetLowering &TLI = DAG.getTargetLoweringInfo();
-  unsigned SmallVTBits = BitWidth - Demanded.countLeadingZeros();
+  unsigned DemandedSize = BitWidth - Demanded.countLeadingZeros();
+  unsigned SmallVTBits = DemandedSize;
   if (!isPowerOf2_32(SmallVTBits))
     SmallVTBits = NextPowerOf2(SmallVTBits);
   for (; SmallVTBits < BitWidth; SmallVTBits = NextPowerOf2(SmallVTBits)) {
@@ -1174,7 +1175,9 @@
                                           Op.getNode()->getOperand(0)),
                               DAG.getNode(ISD::TRUNCATE, dl, SmallVT,
                                           Op.getNode()->getOperand(1)));
-      SDValue Z = DAG.getNode(ISD::ZERO_EXTEND, dl, Op.getValueType(), X);
+      bool NeedZext = DemandedSize > SmallVTBits;
+      SDValue Z = DAG.getNode(NeedZext ? ISD::ZERO_EXTEND : ISD::ANY_EXTEND,
+                              dl, Op.getValueType(), X);
       return CombineTo(Op, Z);
     }
   }

Added: llvm/trunk/test/CodeGen/Generic/dag-combine-crash.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/Generic/dag-combine-crash.ll?rev=170505&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/Generic/dag-combine-crash.ll (added)
+++ llvm/trunk/test/CodeGen/Generic/dag-combine-crash.ll Wed Dec 19 01:39:08 2012
@@ -0,0 +1,21 @@
+; RUN: llc < %s
+
+define void @main()  {
+if.end:
+  br label %block.i.i
+
+block.i.i:
+  %tmpbb = load i8* undef
+  %tmp54 = zext i8 %tmpbb to i64
+  %tmp59 = and i64 %tmp54, 8
+  %tmp60 = add i64 %tmp59, 3691045929300498764
+  %tmp62 = sub i64 %tmp60, 3456506383779105993
+  %tmp63 = xor i64 1050774804270620004, %tmp62
+  %tmp65 = xor i64 %tmp62, 234539545521392771
+  %tmp67 = or i64 %tmp65, %tmp63
+  %tmp71 = xor i64 %tmp67, 6781485823212740913
+  %tmp72 = trunc i64 %tmp71 to i32
+  %tmp74 = lshr i32 2, %tmp72
+  store i32 %tmp74, i32* undef
+  br label %block.i.i
+}