[LLVMbugs] [Bug 12060] New: globalopt miscompilation

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=12060

             Bug #: 12060
           Summary: globalopt miscompilation
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Transformation Utilities
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: richard-llvm at metafoo.co.uk
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


The following code, compiled by clang, produces a correct result (m=13) at -O0
and incorrect result (m=9) at -O1:

  auto s = [](int a) { return [=](int b) { return a + b; }; };
  auto f = s(4);
  auto m = f(9);

Reduced IR:

target datalayout =
"e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"

%closure = type { i32 }

@f = internal global %closure zeroinitializer, align 4
@m = global i32 0, align 4
@llvm.global_ctors = appending global [1 x { i32, void ()* }] [{ i32, void ()*
} { i32 65535, void ()* @_GLOBAL__I_a }]

define internal i32 @lambda(%closure* %this, i32 %b) nounwind uwtable
inlinehint align 2 {
entry:
  %0 = getelementptr inbounds %closure* %this, i32 0, i32 0
  %1 = load i32* %0, align 4
  %add = add nsw i32 %1, %b
  ret i32 %add
}

define internal void @_GLOBAL__I_a() section ".text.startup" {
entry:
  store i32 4, i32* getelementptr inbounds (%closure* @f, i32 0, i32 0)
  %call = call i32 @lambda(%closure* @f, i32 9)
  store i32 %call, i32* @m, align 4
  ret void
}

Manually inlining the call to @lambda removes the miscompile. I'm not sure if
this is related to PR11352, but it appears to be reasonably similar.

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