llvm dev - Apr 2019 - Instruction Execution With Hard Limitation at Runtime

I am trying to give a quota of how many instructions can be run to a
program.
So create a simple function as below:

define void @add_gas(i64 %gasCost) {
__virtual_entry:
  %0 = load i64, i64* @__WAVM__XX__gGasUsed     ### I am sure it exists,
same as the __WAVM__XX__gGasLimit
  %addtmp = add i64 %0, %gasCost
  %1 = load i64, i64* @__WAVM__XX__gGasLimit
  %cmptmp = icmp sgt i64 %addtmp, %1
  br i1 %cmptmp, label %then, label %ifcont

then:                                             ; preds = %__virtual_entry
  call void @exit(i32 1024)
  ret void

ifcont:                                           ; preds = %__virtual_entry
  store i64 %addtmp, i64* @__WAVM__XX__gGasUsed
  ret void
}

; Function Attrs: noreturn nounwind
declare void @exit(i32) #2

Then, I insert this function into the beginning of each basic block the way
as below:
...
ifElse55:                                         ; preds = %ifElseEnd53
  call void @add_gas(i64 1)
  br label %ifElseEnd56

ifElseEnd56:                                      ; preds = %ifElse55,
%ifThen54
  call void @add_gas(i64 2)
  %378 = load i32, i32* %11
  br label %ifElseEnd41

ifElse40:                                         ; preds = %blockEnd23
  call void @add_gas(i64 2)
  %379 = load i32, i32* %11
  br label %ifElseEnd41

ifElseEnd41:                                      ; preds = %ifElse40,
%ifElseEnd56
  call void @add_gas(i64 2)
  %380 = phi i32 [ %378, %ifElseEnd56 ], [ %379, %ifElse40 ]
  br label %ifElseEnd3

ifElseEnd3:                                       ; preds = %ifElseEnd41,
%ifThen1
...

but, when I run my program by RuntimeDyld,  I got an error:

While deleting: i32 %
Use still stuck around after Def is destroyed:  %380 = phi i32 [ %40,
%ifThen1 ], [ <badref>, %ifElseEnd41 ], !dbg !27
Assertion failed: (use_empty() && "Uses remain when a value is
destroyed!"), function ~Value, file
/Users/duanbing/Project/llvm/llvm/lib/IR/Value.cpp, line 90.

Can you give me some tips about what's happened or how to debug this?
Thanks!
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Hi Duan,

On Mon, 1 Apr 2019 at 16:16, Duan Bing via llvm-dev
<llvm-dev at lists.llvm.org> wrote:
> ifElseEnd41:                                      ; preds = %ifElse40,
%ifElseEnd56
>   call void @add_gas(i64 2)
>   %380 = phi i32 [ %378, %ifElseEnd56 ], [ %379, %ifElse40 ]
>   br label %ifElseEnd3
>
>
> Use still stuck around after Def is destroyed:  %380 = phi i32 [ %40,
%ifThen1 ], [ <badref>, %ifElseEnd41 ], !dbg !27
> Assertion failed: (use_empty() && "Uses remain when a value is
destroyed!"), function ~Value, file
/Users/duanbing/Project/llvm/llvm/lib/IR/Value.cpp, line 90.
>
> Can you give me some tips about what's happened or how to debug this?
The issue is that phi instructions must always be at the start of
their basic block (see https://llvm.org/docs/LangRef.html#i-phi). You
can use BasicBlock::getFirstNonPHI to get the correct insertion point
for your call.

Cheers.

Tim.

Got it, thanks!

Tim Northover <t.p.northover at gmail.com> 于2019年4月2日周二 上午12:27写道：
> Hi Duan,
>
> On Mon, 1 Apr 2019 at 16:16, Duan Bing via llvm-dev
> <llvm-dev at lists.llvm.org> wrote:
> > ifElseEnd41:                                      ; preds = %ifElse40,
> %ifElseEnd56
> >   call void @add_gas(i64 2)
> >   %380 = phi i32 [ %378, %ifElseEnd56 ], [ %379, %ifElse40 ]
> >   br label %ifElseEnd3
> >
> >
> > Use still stuck around after Def is destroyed:  %380 = phi i32 [ %40,
> %ifThen1 ], [ <badref>, %ifElseEnd41 ], !dbg !27
> > Assertion failed: (use_empty() && "Uses remain when a
value is
> destroyed!"), function ~Value, file
> /Users/duanbing/Project/llvm/llvm/lib/IR/Value.cpp, line 90.
> >
> > Can you give me some tips about what's happened or how to debug
this?
>
> The issue is that phi instructions must always be at the start of
> their basic block (see https://llvm.org/docs/LangRef.html#i-phi). You
> can use BasicBlock::getFirstNonPHI to get the correct insertion point
> for your call.
>
> Cheers.
>
> Tim.
>
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