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[NaryReassociate] avoid running forever 

Avoid running forever by checking we are not reassociating an expression into
the same form.

Tested with @avoid_infinite_loops in nary-add.ll

llvm-svn: 237269
This commit is contained in:
Jingyue Wu 2015-05-13 18:12:24 +00:00
parent d43f0c5e82
commit c74e33bffe
2 changed files with 19 additions and 4 deletions
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12
llvm/lib/Transforms/Scalar/NaryReassociate.cpp
View File

@ -217,10 +217,14 @@ Instruction *NaryReassociate::tryReassociateAdd(Value *LHS, Value *RHS,
// = (A + RHS) + B or (B + RHS) + A
const SCEV *AExpr = SE->getSCEV(A), *BExpr = SE->getSCEV(B);
const SCEV *RHSExpr = SE->getSCEV(RHS);
if (auto *NewI = tryReassociatedAdd(SE->getAddExpr(AExpr, RHSExpr), B, I))
return NewI;
if (auto *NewI = tryReassociatedAdd(SE->getAddExpr(BExpr, RHSExpr), A, I))
return NewI;
if (BExpr != RHSExpr) {
if (auto *NewI = tryReassociatedAdd(SE->getAddExpr(AExpr, RHSExpr), B, I))
return NewI;
}
if (AExpr != RHSExpr) {
if (auto *NewI = tryReassociatedAdd(SE->getAddExpr(BExpr, RHSExpr), A, I))
return NewI;
}
}
return nullptr;
}

11
llvm/test/Transforms/NaryReassociate/nary-add.ll
View File

@ -196,3 +196,14 @@ define void @iterative(i32 %a, i32 %b, i32 %c) {
ret void
}
define void @avoid_infinite_loop(i32 %a, i32 %b) {
; CHECK-LABEL: @avoid_infinite_loop
%ab = add i32 %a, %b
; CHECK-NEXT: %ab
%ab2 = add i32 %ab, %b
; CHECK-NEXT: %ab2
call void @foo(i32 %ab2)
; CHECK-NEXT: @foo(i32 %ab2)
ret void
}