[LLVMbugs] [Bug 4517] New: missed constant fold

bugzilla-daemon at cs.uiuc.edu bugzilla-daemon at cs.uiuc.edu
Tue Jul 7 22:24:56 PDT 2009


           Summary: missed constant fold
           Product: libraries
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P2
         Component: Scalar Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: nicholas at mxc.ca
                CC: llvmbugs at cs.uiuc.edu

I saw this constant expression in real code after llvm-g++ -O2:

declare extern_weak i32 @0(i64)

define void @foo() {
  br i1 icmp eq (i32 zext (i1 icmp ne (i32 (i64)* @0, i32 (i64)* null) to i32),
i32 0), label %cond_true, label %cond_false
  ret void
  ret void

That branch expression should be reduced to:

  i1 icmp eq (i32 (i64)* @0, i32 (i64)* null)

It's probably not a perf issue, I just happened to see it while examining
something else and didn't want to forget about it.

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