[llvm-commits] [PATCH] Fix a miscompile in memory dependency analysis

[Manman Ren]

Given input:
while.body:
 call void @RunInMode(i32 100) nounwind
 %1 = load i32* %tasksIdle, align 4
 %tobool = icmp eq i32 %1, 0
 br i1 %tobool, label %while.cond.backedge, label %if.then

if.then:
  store i32 0, i32* %tasksIdle, align 4
  call void @TimerCreate(i32* %shouldExit) nounwind
  br label %while.cond.backedge

while.cond.backedge:
 %2 = load i32* %shouldExit, align 4
 %cmp = icmp eq i32 %2, 0
 br i1 %cmp, label %while.body, label %while.cond.while.end_crit_edge

Make sure we are not returning "call RunInMode" does not modify %shouldExit.
Currently, we optimize this into
while.cond.backedge:                              ; preds = %if.then, %while.body
 %1 = phi i32 [ %.pre, %if.then ], [ 0, %while.body ]
 %cmp = icmp eq i32 %1, 0
 br i1 %cmp, label %while.body, label %while.cond.while.end_crit_edge

The proper fix is to check all uses of %shouldExit as long as there is a possible
path from the use to "call RunInMode". The proposed patch uses LoopInfo to approximate the reachability analysis.
Suggestions on how to approximate this are welcome.

Please review, Thanks,

Manman

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