Debug info: If the RegisterCoalescer::reMaterializeTrivialDef() is

eliminating all uses of a vreg, update any DBG_VALUE describing that vreg
to point to the rematerialized register instead.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@223401 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/RegisterCoalescer.cpp

@@ -898,8 +898,20 @@ bool RegisterCoalescer::reMaterializeTrivialDef(CoalescerPair &CP,
 
   // The source interval can become smaller because we removed a use.
   LIS->shrinkToUses(&SrcInt, &DeadDefs);
-  if (!DeadDefs.empty())
+  if (!DeadDefs.empty()) {
+    // If the virtual SrcReg is completely eliminated, update all DBG_VALUEs
+    // to describe DstReg instead.
+    for (MachineRegisterInfo::use_iterator UI = MRI->use_begin(SrcReg),
+         UE = MRI->use_end(); UI != UE; ++UI) {
+      MachineOperand &UseMO = *UI;
+      MachineInstr *UseMI = UseMO.getParent();
+      if (UseMI->isDebugValue()) {
+        UseMO.setReg(DstReg);
+        DEBUG({dbgs() << "\t\tupdated: " <<  *UseMI;});
+      }
+    }
     eliminateDeadDefs();
+  }
 
   return true;
 }

test/DebugInfo/AArch64/coalescing.ll

@@ -0,0 +1,70 @@
+; RUN: llc -filetype=obj %s -o - | llvm-dwarfdump - | FileCheck %s
+;
+; Generated at -Os from:
+; void *my_memcpy(void *dst, const void * src, long n);
+; void* getBytesNoCopy();
+; void start() {
+;   unsigned size;
+;   my_memcpy(&size, getBytesNoCopy(), sizeof(size));
+;   if (size != 0) { }
+; }
+
+; ModuleID = 'test1.cpp'
+target datalayout = "e-m:o-i64:64-i128:128-n32:64-S128"
+target triple = "arm64-apple-ios"
+
+; Function Attrs: nounwind optsize
+define void @_Z5startv() #0 {
+entry:
+  %size = alloca i32, align 4
+  %0 = bitcast i32* %size to i8*, !dbg !15
+  %call = tail call i8* @_Z14getBytesNoCopyv() #3, !dbg !16
+  %call1 = call i8* @_Z9my_memcpyPvPKvl(i8* %0, i8* %call, i64 4) #3, !dbg !15
+  call void @llvm.dbg.value(metadata !{i32* %size}, i64 0, metadata !10, metadata !17), !dbg !18
+  ; CHECK: .debug_info contents:
+  ; CHECK: DW_TAG_variable
+  ; CHECK-NEXT: DW_AT_location
+  ; CHECK-NEXT: DW_AT_name {{.*}}"size"
+  ; CHECK: .debug_loc contents:
+  ; CHECK: Location description: 70 00
+  ret void, !dbg !19
+}
+
+; Function Attrs: optsize
+declare i8* @_Z9my_memcpyPvPKvl(i8*, i8*, i64) #1
+
+; Function Attrs: optsize
+declare i8* @_Z14getBytesNoCopyv() #1
+
+; Function Attrs: nounwind readnone
+declare void @llvm.dbg.value(metadata, i64, metadata, metadata) #2
+
+attributes #0 = { nounwind optsize }
+attributes #1 = { optsize }
+attributes #2 = { nounwind readnone }
+attributes #3 = { nounwind optsize }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!12, !13}
+!llvm.ident = !{!14}
+
+!0 = metadata !{metadata !"0x11\004\00clang version 3.6.0 (trunk 223149) (llvm/trunk 223153)\001\00\000\00\001", metadata !1, metadata !2, metadata !2, metadata !3, metadata !2, metadata !2} ; [ DW_TAG_compile_unit ] [/<stdin>] [DW_LANG_C_plus_plus]
+!1 = metadata !{metadata !"<stdin>", metadata !""}
+!2 = metadata !{}
+!3 = metadata !{metadata !4}
+!4 = metadata !{metadata !"0x2e\00start\00start\00_Z5startv\003\000\001\000\000\00256\001\004", metadata !5, metadata !6, metadata !7, null, void ()* @_Z5startv, null, null, metadata !9} ; [ DW_TAG_subprogram ] [line 3] [def] [scope 4] [start]
+!5 = metadata !{metadata !"test1.cpp", metadata !""}
+!6 = metadata !{metadata !"0x29", metadata !5}    ; [ DW_TAG_file_type ] [/test1.cpp]
+!7 = metadata !{metadata !"0x15\00\000\000\000\000\000\000", null, null, null, metadata !8, null, null, null} ; [ DW_TAG_subroutine_type ] [line 0, size 0, align 0, offset 0] [from ]
+!8 = metadata !{null}
+!9 = metadata !{metadata !10}
+!10 = metadata !{metadata !"0x100\00size\005\000", metadata !4, metadata !6, metadata !11} ; [ DW_TAG_auto_variable ] [size] [line 5]
+!11 = metadata !{metadata !"0x24\00unsigned int\000\0032\0032\000\000\007", null, null} ; [ DW_TAG_base_type ] [unsigned int] [line 0, size 32, align 32, offset 0, enc DW_ATE_unsigned]
+!12 = metadata !{i32 2, metadata !"Dwarf Version", i32 2}
+!13 = metadata !{i32 2, metadata !"Debug Info Version", i32 2}
+!14 = metadata !{metadata !"clang version 3.6.0 (trunk 223149) (llvm/trunk 223153)"}
+!15 = metadata !{i32 6, i32 3, metadata !4, null}
+!16 = metadata !{i32 6, i32 25, metadata !4, null}
+!17 = metadata !{metadata !"0x102"}               ; [ DW_TAG_expression ]
+!18 = metadata !{i32 5, i32 12, metadata !4, null}
+!19 = metadata !{i32 9, i32 1, metadata !4, null}