[LLVMbugs] [Bug 10072] Necessary 'indirectbr' instruction is dropped by optimizer [regression]

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=10072

Bill Wendling <wendling at apple.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |wendling at apple.com
         Resolution|                            |INVALID

--- Comment #1 from Bill Wendling <wendling at apple.com> 2011-06-03 15:19:45 CDT ---
In the particular example you gave, we get this after the first few
optimization passes:


[Irk:llvm] opt < mod.ll -S -mem2reg -globalopt -ipsccp -deadargelim
-instcombine
; ModuleID = '<stdin>'

@xblkx.bbs = internal unnamed_addr constant [9 x i8*] [i8*
blockaddress(@xfuncx, %xblkx.begin), i8* blockaddress(@xfuncx, %xblkx.begin3),
i8* blockaddress(@xfuncx, %xblkx.begin4), i8* blockaddress(@xfuncx,
%xblkx.begin5), i8* blockaddress(@xfuncx, %xblkx.begin6), i8*
blockaddress(@xfuncx, %xblkx.begin7), i8* blockaddress(@xfuncx, %xblkx.begin8),
i8* blockaddress(@xfuncx, %xblkx.begin9), i8* blockaddress(@xfuncx,
%xblkx.end)]

define void @xfuncx() {
escape-string.top:
  %xval202x = call i32 @xfunc5x()
  br label %xlab5x

xlab8x:                                           ; preds = %xlab5x
  %xvaluex = call i32 @xselectorx()
  %xblkx.x = getelementptr [9 x i8*]* @xblkx.bbs, i32 0, i32 %xvaluex
  %xblkx.load = load i8** %xblkx.x
  indirectbr i8* %xblkx.load, [label %xblkx.begin, label %xblkx.begin3, label
%xblkx.begin4, label %xblkx.begin5, label %xblkx.begin6, label %xblkx.begin7,
label %xblkx.begin8, label %xblkx.begin9, label %xblkx.end]

xblkx.begin:                                      ; preds = %xlab8x
  br label %xblkx.end

xblkx.begin3:                                     ; preds = %xlab8x
  br label %xblkx.end

xblkx.begin4:                                     ; preds = %xlab8x
  br label %xblkx.end

xblkx.begin5:                                     ; preds = %xlab8x
  br label %xblkx.end

xblkx.begin6:                                     ; preds = %xlab8x
  br label %xblkx.end

xblkx.begin7:                                     ; preds = %xlab8x
  br label %xblkx.end

xblkx.begin8:                                     ; preds = %xlab8x
  br label %xblkx.end

xblkx.begin9:                                     ; preds = %xlab8x
  br label %xblkx.end

xblkx.end:                                        ; preds = %xblkx.begin9,
%xblkx.begin8, %xblkx.begin7, %xblkx.begin6, %xblkx.begin5, %xblkx.begin4,
%xblkx.begin3, %xblkx.begin, %xlab8x
  %yes.0 = phi i1 [ false, %xblkx.begin ], [ true, %xlab8x ], [ false,
%xblkx.begin9 ], [ false, %xblkx.begin8 ], [ false, %xblkx.begin7 ], [ false,
%xblkx.begin6 ], [ false, %xblkx.begin5 ], [ false, %xblkx.begin4 ], [ false,
%xblkx.begin3 ]
  br i1 %yes.0, label %v2j, label %xlab17x

v2j:                                              ; preds = %xblkx.end
  br label %xlab4x

xlab17x:                                          ; preds = %xblkx.end
  br label %xlab4x

xlab4x:                                           ; preds = %xlab17x, %v2j
  %incr19 = add i32 %xval704x.0, 1
  br label %xlab5x

xlab5x:                                           ; preds = %xlab4x,
%escape-string.top
  %xval704x.0 = phi i32 [ 0, %escape-string.top ], [ %incr19, %xlab4x ]
  %xval10x = icmp ult i32 %xval704x.0, %xval202x
  br i1 %xval10x, label %xlab8x, label %xlab9x

xlab9x:                                           ; preds = %xlab5x
  ret void
}

The "simplifycfg" pass comes along and realizes that the result of all
indirectbr branches wind up in the same place, and so eliminates it:


[Irk:llvm] opt < mod.ll -S -mem2reg -globalopt -ipsccp -deadargelim
-instcombine -simplifycfg
; ModuleID = '<stdin>'

@xblkx.bbs = internal unnamed_addr constant [9 x i8*] [i8*
blockaddress(@xfuncx, %xlab4x), i8* blockaddress(@xfuncx, %xlab4x), i8*
blockaddress(@xfuncx, %xlab4x), i8* blockaddress(@xfuncx, %xlab4x), i8*
blockaddress(@xfuncx, %xlab4x), i8* blockaddress(@xfuncx, %xlab4x), i8*
blockaddress(@xfuncx, %xlab4x), i8* blockaddress(@xfuncx, %xlab4x), i8*
blockaddress(@xfuncx, %xlab4x)]

define void @xfuncx() {
escape-string.top:
  %xval202x = call i32 @xfunc5x()
  br label %xlab5x

xlab8x:                                           ; preds = %xlab5x
  %xvaluex = call i32 @xselectorx()
  br label %xlab4x

xlab4x:                                           ; preds = %xlab8x
  %incr19 = add i32 %xval704x.0, 1
  br label %xlab5x

xlab5x:                                           ; preds = %xlab4x,
%escape-string.top
  %xval704x.0 = phi i32 [ 0, %escape-string.top ], [ %incr19, %xlab4x ]
  %xval10x = icmp ult i32 %xval704x.0, %xval202x
  br i1 %xval10x, label %xlab8x, label %xlab9x

xlab9x:                                           ; preds = %xlab5x
  ret void
}

Do you have another testcase which would show the failure? I.e., where all of
the branches of the indirectbr don't execute the same code? If so, please
reopen this bug.

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