[llvm-bugs] [Bug 28964] New: [SimplifyCFG] failure to sink common function call below if/else

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=28964

            Bug ID: 28964
           Summary: [SimplifyCFG] failure to sink common function call
                    below if/else
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Transformation Utilities
          Assignee: unassignedbugs at nondot.org
          Reporter: spatel+llvm at rotateright.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Forking this off from bug 28957:

extern int bar(int);
int foo(int x) {
  if (x == 1)
    return bar(1);
  else
    return bar(-1);
}

Or as optimized IR:

define i32 @foo(i32 %x) {
entry:
  %cmp = icmp eq i32 %x, 1
  br i1 %cmp, label %if.then, label %if.else

if.then:            
  %call = tail call i32 @bar(i32 1) #2
  br label %return

if.else:                 
  %call1 = tail call i32 @bar(i32 -1) #2
  br label %return

return:                 
  %retval.0 = phi i32 [ %call, %if.then ], [ %call1, %if.else ]
  ret i32 %retval.0
}

declare i32 @bar(i32)

--------------------------------------------------------------------------

I think SimplifyCFG should transform this to the equivalent of:

int goo(int x) {
  if (x == 1)
    x = 1;
  else
    x = -1;
  return bar(x);
}

which is this in IR:

define i32 @goo(i32 %x) local_unnamed_addr #0 {
  %cmp = icmp eq i32 %x, 1
  %sel = select i1 %cmp, i32 1, i32 -1
  %call = tail call i32 @bar(i32 %sel)
  ret i32 %call
}

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