[PATCH] D11933: Extending debug ranges

[Vikram TV via llvm-commits]

tvvikram added a comment.

I compiled your test case with clang -O1 and here is the input to DBG_VALUE fixup pass (output of StackMapLivenessAnalysis).

  # *** IR Dump After StackMap Liveness Analysis ***:
  # Machine code for function f: Post SSA
  Frame Objects:
    fi#0: size=4, align=4, at location [SP-4]
  
  BB#0: derived from LLVM BB %entry
    PUSH64r %RAX<undef>, %RSP<imp-def>, %RSP<imp-use>; flags: FrameSetup dbg:r.c:3:7
    CFI_INSTRUCTION <call frame instruction>
    DBG_VALUE 23, 0, !"x", <!14>; line no:3
    MOV32mi %RSP, 1, %noreg, 4, %noreg, 23; mem:ST4[%x](tbaa=!17) dbg:r.c:3:7
    %RDI<def> = LEA64r %RSP, 1, %noreg, 4, %noreg
    DBG_VALUE %RDI, 0, !"x", <!14>; line no:3 indirect
    CALL64pcrel32 <ga:@g>, <regmask>, %RSP<imp-use>, %RDI<imp-use>, %RSP<imp-def>; dbg:r.c:4:3
    %EAX<def> = MOV32rm %RSP, 1, %noreg, 4, %noreg; mem:LD4[%x](tbaa=!17) dbg:r.c:5:7
    CMP32ri8 %EAX, 42, %EFLAGS<imp-def>; dbg:r.c:5:7
    JNE_1 <BB#2>, %EFLAGS<imp-use>
      Successors according to CFG: BB#1(16) BB#2(16)
  
  BB#1: derived from LLVM BB %if.then
      Live Ins: %EAX
      Predecessors according to CFG: BB#0
    DBG_VALUE 23, 0, !"x", <!14>; line no:3
    %EAX<def,tied1> = INC32r %EAX<kill,tied0>, %EFLAGS<imp-def,dead>; dbg:r.c:6:5
    DBG_VALUE %EAX, %noreg, !"x", <!14>; line no:3
    MOV32mr %RSP, 1, %noreg, 4, %noreg, %EAX<kill>; mem:ST4[%x](tbaa=!17) dbg:r.c:6:5
      Successors according to CFG: BB#2
  
  BB#2: derived from LLVM BB %if.end
      Predecessors according to CFG: BB#0 BB#1
    DBG_VALUE 23, 0, !"x", <!14>; line no:3
    %EAX<def> = MOV32rm %RSP, 1, %noreg, 4, %noreg; mem:LD4[%x](tbaa=!17) dbg:r.c:7:10
    %RDX<def> = POP64r %RSP<imp-def>, %RSP<imp-use>; dbg:r.c:7:3
    RETQ %EAX; dbg:r.c:7:3
  
  # End machine code for function f.

The DBG_VALUE instr for "x" is already present in BB#2 and only "x" in RDI got propagated to BB#1.

With respect to handling variables having constant value, an early thought is to have ranges for them until the variable is moved to register. When the variable is moved to register, it will end all previous ranges of that variable because the move to register will mean that it may be operated on and the value may change. The current patch handles only register locations.


http://reviews.llvm.org/D11933