Fix constant folding through bitcasts by no longer relying on undefined behaviour...

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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163703 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index d85d41bd86ac452b5eb475a4771729cf3a2f202e..b515fbaf6005c01d7fb1ac1503d005dd4b8993eb 100644 (file)
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2454,9 +2454,9 @@ SDValue SelectionDAG::getNode(unsigned Opcode, DebugLoc DL,
     }
     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);

diff --git a/test/CodeGen/ARM/constants.ll b/test/CodeGen/ARM/constants.ll
index 0ac8b48d390f96124cab5034a840a76e24a1adf5..3baa103e3d5df10842726970798c2246c6fb1469 100644 (file)
--- a/test/CodeGen/ARM/constants.ll
+++ b/test/CodeGen/ARM/constants.ll
@@ -45,6 +45,16 @@ r:
         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,