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[SimplifyCFG] Check PHI uses more accurately 

PR30292 showed a case where our PHI checking wasn't correct. We were checking that all values were used by the same PHI before deciding to sink, but we weren't checking that the incoming values for that PHI were what we expected. As a result, we had to bail out after block splitting which caused us to never reach a steady state in SimplifyCFG.

Fixes PR30292.

llvm-svn: 280790
This commit is contained in:
James Molloy 2016-09-07 08:15:54 +00:00
parent 42c83f131e
commit bf1837d9c9
2 changed files with 28 additions and 1 deletions
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4
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -1403,7 +1403,9 @@ static bool canSinkInstructions(
auto *PNUse = dyn_cast<PHINode>(*I0->user_begin());
if (!all_of(Insts, [&PNUse](const Instruction *I) -> bool {
auto *U = cast<Instruction>(*I->user_begin());
return U == PNUse || U->getParent() == I->getParent();
return (PNUse &&
PNUse->getIncomingValueForBlock(I->getParent()) == I) ||
U->getParent() == I->getParent();
}))
return false;
}

25
llvm/test/Transforms/SimplifyCFG/sink-common-code.ll
View File

@ -585,6 +585,31 @@ if.end:
; CHECK: store
; CHECK: store
; The phi is confusing - both add instructions are used by it, but
; not on their respective unconditional arcs. It should not be
; optimized.
define void @test_pr30292(i1 %cond, i1 %cond2, i32 %a, i32 %b) {
entry:
%add1 = add i32 %a, 1
br label %succ
one:
br i1 %cond, label %two, label %succ
two:
call void @g()
%add2 = add i32 %a, 1
br label %succ
succ:
%p = phi i32 [ 0, %entry ], [ %add1, %one ], [ %add2, %two ]
br label %one
}
declare void @g()
; CHECK-LABEL: test_pr30292
; CHECK: phi i32 [ 0, %entry ], [ %add1, %succ ], [ %add2, %two ]
; CHECK: !0 = !{!1, !1, i64 0}
; CHECK: !1 = !{!"float", !2}
; CHECK: !2 = !{!"an example type tree"}