[MIPS] BuildCondBr should preserve MO flags

While simplifying branches in the MachineInstr representation, the
routine BuildCondBr must preserve flags on register MachineOperands. In
particular, it must preserve the <undef> flag.

This fixes a bug that is unlikely to occur in any real scenario, but
which bugpoint is likely to introduce.

Patch By Nick Johnson!

Reviewers: ahatanak, sdardis

Differential Revision: https://reviews.llvm.org/D34041

llvm-svn: 305290

llvm/lib/Target/Mips/MipsInstrInfo.cpp

@@ -103,12 +103,9 @@ void MipsInstrInfo::BuildCondBr(MachineBasicBlock &MBB, MachineBasicBlock *TBB,
   MachineInstrBuilder MIB = BuildMI(&MBB, DL, MCID);
 
   for (unsigned i = 1; i < Cond.size(); ++i) {
-    if (Cond[i].isReg())
-      MIB.addReg(Cond[i].getReg());
-    else if (Cond[i].isImm())
-      MIB.addImm(Cond[i].getImm());
-    else
-       assert(false && "Cannot copy operand");
+    assert((Cond[i].isImm() || Cond[i].isReg()) &&
+           "Cannot copy operand for conditional branch!");
+    MIB.add(Cond[i]);
   }
   MIB.addMBB(TBB);
 }

llvm/test/CodeGen/Mips/brundef.ll

@@ -0,0 +1,26 @@
+; RUN: llc -march=mips -mcpu=mips32 -verify-machineinstrs -o /dev/null < %s 
+; Confirm that MachineInstr branch simplification preserves
+; register operand flags, such as the <undef> flag.
+
+define void @ham() {
+bb:
+  %tmp = alloca i32, align 4
+  %tmp13 = ptrtoint i32* %tmp to i32
+  %tmp70 = icmp eq i32 undef, -1
+  br i1 %tmp70, label %bb72, label %bb40
+
+bb72:                                             ; preds = %bb72, %bb
+  br i1 undef, label %bb40, label %bb72
+
+bb40:                                             ; preds = %bb72, %bb
+  %tmp41 = phi i32 [ %tmp13, %bb72 ], [ %tmp13, %bb ]
+  %tmp55 = inttoptr i32 %tmp41 to i32*
+  %tmp58 = insertelement <2 x i32*> undef, i32* %tmp55, i32 1
+  br label %bb59
+
+bb59:                                             ; preds = %bb59, %bb40
+  %tmp60 = phi <2 x i32*> [ %tmp61, %bb59 ], [ %tmp58, %bb40 ]
+  %tmp61 = getelementptr i32, <2 x i32*> %tmp60, <2 x i32> <i32 -1, i32 1>
+  %tmp62 = extractelement <2 x i32*> %tmp61, i32 1
+  br label %bb59
+}