R600: Bug 20982 - Avoid undefined left shift of negative value

[arsenm]

Summary

I'm not sure what the hardware actually does, so don't bother trying to fold it for now.

[arsenm]

r218057

lib/Target/R600/AMDGPUISelLowering.cpp

       return DAG.getZeroExtendInReg(BitsFrom, DL, SmallVT);
     }
 
-    if (ConstantSDNode *Val = dyn_cast<ConstantSDNode>(N->getOperand(0))) {
+    if (ConstantSDNode *CVal = dyn_cast<ConstantSDNode>(N->getOperand(0))) {
       if (Signed) {
+        // Avoid undefined left shift of a negative in the constant fold.
+        // TODO: I'm not sure what the behavior of the hardware is, this should
+        // probably follow that instead.
+        int32_t Val = CVal->getSExtValue();
+        if (Val < 0)
+          return SDValue();
+
         return constantFoldBFE<int32_t>(DAG,
-                                        Val->getSExtValue(),
+                                        Val,
                                         OffsetVal,
                                         WidthVal);
       }
 
       return constantFoldBFE<uint32_t>(DAG,
-                                       Val->getZExtValue(),
+                                       CVal->getZExtValue(),
                                        OffsetVal,
                                        WidthVal);
     }

test/CodeGen/R600/llvm.AMDGPU.bfe.i32.ll

 ; RUN: llc -march=r600 -mcpu=SI -verify-machineinstrs < %s | FileCheck -check-prefix=SI -check-prefix=FUNC %s
 ; RUN: llc -march=r600 -mcpu=redwood -show-mc-encoding -verify-machineinstrs < %s | FileCheck -check-prefix=EG -check-prefix=FUNC %s
 
-; http://llvm.org/bugs/show_bug.cgi?id=20982
-; REQUIRES: not_ubsan
-
 declare i32 @llvm.AMDGPU.bfe.i32(i32, i32, i32) nounwind readnone
 
 ; FUNC-LABEL: @bfe_i32_arg_arg_arg

   ret void
 }
 
+; FIXME: This should fold to something
 ; FUNC-LABEL: @bfe_i32_constant_fold_test_16
-; SI-NOT: BFE
-; SI: V_MOV_B32_e32 [[VREG:v[0-9]+]], -1
+; SI: S_BFE_I32 [[SREG:s[0-9]+]], -1, 0x70001
+; SI: V_MOV_B32_e32 [[VREG:v[0-9]+]], [[SREG]]
 ; SI: BUFFER_STORE_DWORD [[VREG]],
 ; SI: S_ENDPGM
-; EG-NOT: BFE
+
 define void @bfe_i32_constant_fold_test_16(i32 addrspace(1)* %out) nounwind {
   %bfe_i32 = call i32 @llvm.AMDGPU.bfe.i32(i32 4294967295, i32 1, i32 7) nounwind readnone
   store i32 %bfe_i32, i32 addrspace(1)* %out, align 4