[LLVMbugs] [Bug 7136] New: InstCombine lowerize w/TD to lose type information

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=7136

           Summary: InstCombine lowerize w/TD to lose type information
           Product: libraries
           Version: trunk
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Scalar Optimizations
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: geek4civic at gmail.com
                CC: llvmbugs at cs.uiuc.edu


A simple example to allocate and initialize an object.

---
define %struct.A* @foo(i32 %a, i32 %b) nounwind {
entry:
  %0 = call noalias i8* @malloc(i32 8) nounwind   ; <i8*> [#uses=1]
  %1 = bitcast i8* %0 to %struct.A*               ; <%struct.A*> [#uses=4]
  %2 = icmp ne %struct.A* %1, null                ; <i1> [#uses=1]
  br i1 %2, label %bb, label %return

bb:
  %3 = getelementptr inbounds %struct.A* %1, i32 0, i32 0 ; <i32*> [#uses=1]
  store i32 %a, i32* %3, align 4
  %4 = getelementptr inbounds %struct.A* %1, i32 0, i32 1 ; <i32*> [#uses=1]
  store i32 %b, i32* %4, align 4
  br label %return

return:
  ret %struct.A* %1
}
---

The pass "InstCombine" strips and lowerizes type information as below.

---
define %struct.A* @foo(i32 %a, i32 %b) nounwind {
entry:
  %0 = call noalias i8* @malloc(i32 8) nounwind   ; <i8*> [#uses=4]
  %1 = bitcast i8* %0 to %struct.A*               ; <%struct.A*> [#uses=1]
  %2 = icmp eq i8* %0, null                       ; <i1> [#uses=1]
  br i1 %2, label %return, label %bb

bb:                                               ; preds = %entry
  %3 = bitcast i8* %0 to i32*                     ; <i32*> [#uses=1]
  store i32 %a, i32* %3, align 4
  %4 = getelementptr inbounds i8* %0, i32 4       ; <i8*> [#uses=1]
  %5 = bitcast i8* %4 to i32*                     ; <i32*> [#uses=1]
  store i32 %b, i32* %5, align 4
  br label %return

return:                                           ; preds = %bb, %entry
  ret %struct.A* %1
}
---

It makes following analysis harder, I guess.

I think, it would not needed to convert when;
* origBase has generic pointer type (eg. i8 *)
* origBase is derived from allocation
 at InstCombiner::commonPointerCastTransforms(CastInst &CI);


(FYI, my environment as below)
---
target datalayout =
"e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32"
target triple = "i386-mingw32"

%struct.A = type { i32, i32 }

declare noalias i8* @malloc(i32) nounwind
---

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