[llvm-bugs] [Bug 35038] New: GVN drops nonnull metadata

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=35038

            Bug ID: 35038
           Summary: GVN drops nonnull metadata
           Product: libraries
           Version: 5.0
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Scalar Optimizations
          Assignee: unassignedbugs at nondot.org
          Reporter: yyc1992 at gmail.com
                CC: llvm-bugs at lists.llvm.org

Very similar to https://bugs.llvm.org/show_bug.cgi?id=30597 and
https://bugs.llvm.org/show_bug.cgi?id=31142 but for GVN this time.

Code to reproduce:

```
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

define i8* @f(i8** %v0, i8** %v1) {
top:
  %v2 = load i8*, i8** %v0, !nonnull !0
  store i8* %v2, i8** %v1
  %v3 = load i8*, i8** %v1
  ret i8* %v3
}

!0 = !{}
```

Running GVN produces

```
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

define i8* @f(i8** %v0, i8** %v1) {
top:
  %v2 = load i8*, i8** %v0
  store i8* %v2, i8** %v1
  ret i8* %v2
}
```

while running instcombine produces

```
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

define i8* @f(i8** %v0, i8** %v1) {
top:
  %0 = bitcast i8** %v0 to i64*
  %v21 = load i64, i64* %0, align 8, !range !0
  %1 = bitcast i8** %v1 to i64*
  store i64 %v21, i64* %1, align 8
  %v3.cast = inttoptr i64 %v21 to i8*
  ret i8* %v3.cast
}

!0 = !{i64 1, i64 0}
```

The GVN version has deleted the `!nonnull` metadata on the load.

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