http://llvm.org/bugs/show_bug.cgi?id=10254
Summary: Phi with identical arguments not optimized
Product: libraries
Version: trunk
Platform: PC
OS/Version: All
Status: NEW
Severity: normal
Priority: P
Component: Scalar Optimizations
AssignedTo: [email protected]
ReportedBy: [email protected]
CC: [email protected]
Created an attachment (id=6818)
--> (http://llvm.org/bugs/attachment.cgi?id=6818)
test.ll
I was curious why early tail dup in CodeGen was seeing trivial bb like
foo:
jmp bar
since I would expect simplifycfg to handle them.
One case I found is attached. We have code that looks like:
----------------------------
bb0: ; preds = %for.body7.i
%gep0 = getelementptr inbounds i8* %call.i.i.i.i, i64 8
%cast0 = bitcast i8* %gep0 to %"class.llvm::MallocAllocator"**
br label %bb2
bb1: ; preds = %for.body7.i
%second.i.i.i.i.i = getelementptr inbounds i8* %call.i.i.i.i, i64 8
%cast1 = bitcast i8* %second.i.i.i.i.i to %"class.llvm::MallocAllocator"**
Use of cast1
br label %bb2
bb2: ; preds = %bb1, %bb0
%.pre-phi.i.i.i = phi %"class.llvm::MallocAllocator"** [ %cast0, %bb0 ], [
%cast1, %bb1 ]
----------------------------
codegenprepare will move gep0 and cast0, making bb0 empty, but that is too late
for simplifycfg. One way to optimize this early would be to move both the gep
and cast to for.body7.i and remove the phi. After that simplifycfg would remove
bb0.
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