This reapplies r207235 with an additional bugfixes caught by the msan
buildbot - do not insert debug intrinsics before phi nodes.

Debug info for optimized code: Support variables that are on the stack and
described by DBG_VALUEs during their lifetime.

Previously, when a variable was at a FrameIndex for any part of its
lifetime, this would shadow all other DBG_VALUEs and only a single
fbreg location would be emitted, which in fact is only valid for a small
range and not the entire lexical scope of the variable. The included
dbg-value-const-byref testcase demonstrates this.

This patch fixes this by
Local
- emitting dbg.value intrinsics for allocas that are passed by reference
- dropping all dbg.declares (they are now fully lowered to dbg.values)
SelectionDAG
- renamed constructors for SDDbgValue for better readability.
- fix UserValue::match() to handle indirect values correctly
- not inserting an MMI table entries for dbg.values that describe allocas.
- lowering dbg.values that describe allocas into *indirect* DBG_VALUEs.
CodeGenPrepare
- leaving dbg.values for an alloca were they are (see comment)
Other
- regenerated/updated instcombine.ll testcase and included source

rdar://problem/16679879
http://reviews.llvm.org/D3374

llvm-svn: 207269
diff --git a/llvm/test/DebugInfo/X86/formal_parameter.ll b/llvm/test/DebugInfo/X86/formal_parameter.ll
index 04362d9..3445f46 100644
--- a/llvm/test/DebugInfo/X86/formal_parameter.ll
+++ b/llvm/test/DebugInfo/X86/formal_parameter.ll
@@ -34,6 +34,7 @@
   ;
   ; LOWERING: call void @llvm.dbg.value{{.*}}, !dbg ![[LOC:.*]]
   ; LOWERING: call void @llvm.dbg.value{{.*}}, !dbg ![[LOC]]
+  ; LOWERING: call void @llvm.dbg.value{{.*}}, !dbg ![[LOC]]
 %0 = load i32* %map.addr, align 4, !dbg !20, !tbaa !15
   %call1 = call i32 (i32, ...)* bitcast (i32 (...)* @verify to i32 (i32, ...)*)(i32 %0) #3, !dbg !20
   ret void, !dbg !22