Add value numbers when spilling dead defs.

When spilling around an instruction with a dead def, remember to add a
value number for the def.

The missing value number wouldn't normally create problems since there
would be an incoming live range as well.  However, due to another bug
we could spill a dead V_SET0 instruction which doesn't read any values.

The missing value number caused an empty live range to be created which
is dangerous since it doesn't interfere with anything.

This fixes part of PR11125.

llvm-svn: 141923

2 files changed, 28 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/InlineSpiller.cpp b/llvm/lib/CodeGen/InlineSpiller.cpp
index b63611b94c1..726af469657 100644
--- a/llvm/lib/CodeGen/InlineSpiller.cpp
+++ b/llvm/lib/CodeGen/InlineSpiller.cpp
@@ -1187,8 +1187,16 @@ void InlineSpiller::spillAroundUses(unsigned Reg) {
     DEBUG(dbgs() << "\trewrite: " << Idx << '\t' << *MI);
 
     // FIXME: Use a second vreg if instruction has no tied ops.
-    if (Writes && hasLiveDef)
+    if (Writes) {
+     if (hasLiveDef)
       insertSpill(NewLI, OldLI, Idx, MI);
+     else {
+       // This instruction defines a dead value.  We don't need to spill it,
+       // but do create a live range for the dead value.
+       VNInfo *VNI = NewLI.getNextValue(Idx, 0, LIS.getVNInfoAllocator());
+       NewLI.addRange(LiveRange(Idx, Idx.getNextSlot(), VNI));
+     }
+    }
 
     DEBUG(dbgs() << "\tinterval: " << NewLI << '\n');
   }
diff --git a/llvm/test/CodeGen/X86/2011-10-11-SpillDead.ll b/llvm/test/CodeGen/X86/2011-10-11-SpillDead.ll
new file mode 100644
index 00000000000..8e70d6543ac
--- /dev/null
+++ b/llvm/test/CodeGen/X86/2011-10-11-SpillDead.ll
@@ -0,0 +1,19 @@
+; RUN: llc < %s -verify-regalloc
+; PR11125
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.7"
+
+; The inline asm takes %x as a GR32_ABCD virtual register.
+; The call to @g forces a spill of that register.
+;
+; The asm has a dead output tied to %x.
+; Verify that the spiller creates a value number for that dead def.
+;
+define void @f(i32 %x) nounwind uwtable ssp {
+entry:
+  tail call void @g() nounwind
+  %0 = tail call i32 asm sideeffect "foo $0", "=Q,0,~{ebx},~{dirflag},~{fpsr},~{flags}"(i32 %x) nounwind
+  ret void
+}
+
+declare void @g()