misched: Fix the DAG builder to handle an undef operand at ExitSU.

Assertion failed: (VNI && "No value to read by operand")
rdar://12790267.

llvm-svn: 169071

2 files changed, 28 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp b/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
index 2b00b596d3b..fd75576c786 100644
--- a/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
+++ b/llvm/lib/CodeGen/ScheduleDAGInstrs.cpp
@@ -210,7 +210,8 @@ void ScheduleDAGInstrs::addSchedBarrierDeps() {
         Uses[Reg].push_back(PhysRegSUOper(&ExitSU, -1));
       else {
         assert(!IsPostRA && "Virtual register encountered after regalloc.");
-        addVRegUseDeps(&ExitSU, i);
+        if (MO.readsReg()) // ignore undef operands
+          addVRegUseDeps(&ExitSU, i);
       }
     }
   } else {
diff --git a/llvm/test/CodeGen/X86/misched-new.ll b/llvm/test/CodeGen/X86/misched-new.ll
index cec04b534fb..a39ea03af55 100644
--- a/llvm/test/CodeGen/X86/misched-new.ll
+++ b/llvm/test/CodeGen/X86/misched-new.ll
@@ -51,3 +51,29 @@ if.end:                                           ; preds = %if.then, %entry
 }
 
 declare void @bar(i32,i32)
+
+; Test that the DAG builder can handle an undef vreg on ExitSU.
+; CHECK: hasundef
+; CHECK: call
+
+%t0 = type { i32, i32, i8 }
+%t6 = type { i32 (...)**, %t7* }
+%t7 = type { i32 (...)** }
+
+define void @hasundef() unnamed_addr uwtable ssp align 2 {
+  %1 = alloca %t0, align 8
+  br i1 undef, label %3, label %2
+
+; <label>:2                                       ; preds = %0
+  unreachable
+
+; <label>:3                                       ; preds = %0
+  br i1 undef, label %4, label %5
+
+; <label>:4                                       ; preds = %3
+  call void undef(%t6* undef, %t0* %1)
+  unreachable
+
+; <label>:5                                       ; preds = %3
+  ret void
+}