[llvm-commits] [llvm] r163703 - in /llvm/trunk: lib/CodeGen/SelectionDAG/SelectionDAG.cpp test/CodeGen/ARM/constants.ll

[Kristof Beyls]

Author: kbeyls
Date: Wed Sep 12 06:25:02 2012
New Revision: 163703

URL: http://llvm.org/viewvc/llvm-project?rev=163703&view=rev
Log:
Fix constant folding through bitcasts by no longer relying on undefined behaviour (converting NaN values between float and double).

SelectionDAG::getConstantFP(double Val, EVT VT, bool isTarget);
should not be used when Val is not a simple constant (as the comment in
SelectionDAG.h indicates). This patch avoids using this function
when folding an unknown constant through a bitcast, where it cannot be
guaranteed that Val will be a simple constant.


Modified:
    llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
    llvm/trunk/test/CodeGen/ARM/constants.ll

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp?rev=163703&r1=163702&r2=163703&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp Wed Sep 12 06:25:02 2012
@@ -2454,9 +2454,9 @@
     }
     case ISD::BITCAST:
       if (VT == MVT::f32 && C->getValueType(0) == MVT::i32)
-        return getConstantFP(Val.bitsToFloat(), VT);
+        return getConstantFP(APFloat(Val), VT);
       else if (VT == MVT::f64 && C->getValueType(0) == MVT::i64)
-        return getConstantFP(Val.bitsToDouble(), VT);
+        return getConstantFP(APFloat(Val), VT);
       break;
     case ISD::BSWAP:
       return getConstant(Val.byteSwap(), VT);

Modified: llvm/trunk/test/CodeGen/ARM/constants.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/constants.ll?rev=163703&r1=163702&r2=163703&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/constants.ll (original)
+++ llvm/trunk/test/CodeGen/ARM/constants.ll Wed Sep 12 06:25:02 2012
@@ -45,6 +45,16 @@
         ret void
 }
 
+define i32 @f8() nounwind {
+; Check that constant propagation through (i32)-1 => (float)Nan => (i32)-1
+; gives expected result
+; CHECK: f8
+; CHECK: mvn r0, #0
+        %tmp0 = bitcast i32 -1 to float
+        %tmp1 = bitcast float %tmp0 to i32
+        ret i32 %tmp1
+}
+
 %t1 = type { <3 x float>, <3 x float> }
 
 @const1 = global %t1 { <3 x float> zeroinitializer,