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[LV] Remove wrong assumption about LCSSA

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The LCSSA pass itself will not generate several redundant PHI nodes in a single
exit block. However, such redundant PHI nodes don't violate LCSSA form, and may
be introduced by passes that preserve LCSSA, and/or preserved by the LCSSA pass
itself. So, assuming a single PHI node per exit block is not safe.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@275217 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Michael Kuperstein 2016-07-12 21:24:06 +00:00
parent e0c5ceae90
commit 6449d7c4a9
2 changed files with 25 additions and 5 deletions
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5
lib/Transforms/Vectorize/LoopVectorize.cpp
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@ -3112,9 +3112,6 @@ void InnerLoopVectorizer::fixupIVUsers(PHINode *OrigPhi,
// value (the value that feeds into the phi from the loop latch).
// We allow both, but they, obviously, have different values.
// We only expect at most one of each kind of user. This is because LCSSA will
// canonicalize the users to a single PHI node per exit block, and we
// currently only vectorize loops with a single exit.
assert(OrigLoop->getExitBlock() && "Expected a single exit block");
// An external user of the last iteration's value should see the value that
@ -3132,7 +3129,6 @@ void InnerLoopVectorizer::fixupIVUsers(PHINode *OrigPhi,
auto *User = cast<PHINode>(UI);
if (User->getBasicBlockIndex(MiddleBlock) == -1)
User->addIncoming(EndValue, MiddleBlock);
break;
}
}
@ -3159,7 +3155,6 @@ void InnerLoopVectorizer::fixupIVUsers(PHINode *OrigPhi,
Value *Escape = II.transform(B, CMO, PSE.getSE(), DL);
Escape->setName("ind.escape");
User->addIncoming(Escape, MiddleBlock);
break;
}
}
}

25
test/Transforms/LoopVectorize/iv_outside_user.ll
View File

@ -108,3 +108,28 @@ for.body:
for.end:
ret i32* %inc.lag1
}
; CHECK-LABEL: @multiphi
; CHECK-LABEL: scalar.ph:
; CHECK: %bc.resume.val = phi i32 [ %n.vec, %middle.block ], [ 0, %entry ]
; CHECK-LABEL: for.end:
; CHECK: %phi = phi i32 [ {{.*}}, %for.body ], [ %n.vec, %middle.block ]
; CHECK: %phi2 = phi i32 [ {{.*}}, %for.body ], [ %n.vec, %middle.block ]
; CHECK: store i32 %phi2, i32* %p
; CHECK: ret i32 %phi
define i32 @multiphi(i32 %k, i32* %p) {
entry:
br label %for.body
for.body:
%inc.phi = phi i32 [ 0, %entry ], [ %inc, %for.body ]
%inc = add nsw i32 %inc.phi, 1
%cmp = icmp eq i32 %inc, %k
br i1 %cmp, label %for.end, label %for.body
for.end:
%phi = phi i32 [ %inc, %for.body ]
%phi2 = phi i32 [ %inc, %for.body ]
store i32 %phi2, i32* %p
ret i32 %phi
}