[llvm-bugs] [Bug 43616] New: [globalopt] optimization leaves store to a constant global

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=43616

            Bug ID: 43616
           Summary: [globalopt] optimization leaves store to a constant
                    global
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Interprocedural Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: juneyoung.lee at sf.snu.ac.kr
                CC: llvm-bugs at lists.llvm.org

Created attachment 22643
  --> https://bugs.llvm.org/attachment.cgi?id=22643&action=edit
input

```
$ opt -version
LLVM (http://llvm.org/):
  LLVM version 10.0.0svn
  Optimized build with assertions.
  Default target: x86_64-apple-darwin19.0.0
  Host CPU: skylake

$ cat input.ll
declare {}* @llvm.invariant.start.p0i8(i64 %size, i8* nocapture %ptr)

define void @test1(i8* %ptr) {
  call {}* @llvm.invariant.start.p0i8(i64 4, i8* %ptr)
  ret void
}

@object1 = global i32 0
define void @ctor1() {
  store i32 -1, i32* @object1
  %A = bitcast i32* @object1 to i8*
  call void @test1(i8* %A)
  ret void
}

@llvm.global_ctors = appending constant
  [1 x { i32, void ()*, i8* }]
  [ { i32, void ()*, i8* } { i32 65535, void ()* @ctor1, i8* null } ]

$ opt -globalopt -S -o - input.ll
@object1 = constant i32 -1
@llvm.global_ctors = appending constant [0 x { i32, void ()*, i8* }]
zeroinitializer

; Function Attrs: argmemonly nounwind willreturn
declare {}* @llvm.invariant.start.p0i8(i64 immarg, i8* nocapture) #0

define void @test1(i8* %ptr) local_unnamed_addr {
  %1 = call {}* @llvm.invariant.start.p0i8(i64 4, i8* %ptr)
  ret void
}

define void @ctor1() local_unnamed_addr {
  store i32 -1, i32* @object1
  %A = bitcast i32* @object1 to i8*
  call void @test1(i8* %A)
  ret void
}

attributes #0 = { argmemonly nounwind willreturn }
```

Running -globalopt leaves a store to @object1, which is a constant global,
which may cause crash because LangRef states that it can be placed in the
read-only section of an executable.

LangRef says:
A variable may be defined as a global constant, which indicates that the
contents of the variable will never be modified (enabling better optimization,
allowing the global data to be placed in the read-only section of an
executable, etc).

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