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[LoopVersioning] Don't modify the list that we iterate over in addPHINodes 

Summary:
In LoopVersioning::addPHINodes we need to iterate over all
users for a value "Inst", and if the user is outside of the
VersionedLoop we should replace the use of "Inst" by using
the value "PN" instead.

Replacing the use of "Inst" for a user of "Inst" also means
that Inst->users() is modified. So it is not safe to do the
replace while iterating over Inst->users() as we used to do.
This patch splits the task into two steps. First we iterate
over Inst->users() to find all users that should be updated.
Those users are saved into a local data structure on the stack.
And then, in the second step, we do the actual updates. This
time iterating over the local data structure.

Reviewers: mzolotukhin, anemet

Reviewed By: mzolotukhin

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D47134

llvm-svn: 332958
This commit is contained in:
Bjorn Pettersson 2018-05-22 08:33:02 +00:00
parent 844663353d
commit fecef6be9e
2 changed files with 71 additions and 3 deletions
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9
llvm/lib/Transforms/Utils/LoopVersioning.cpp
View File

@ -140,9 +140,12 @@ void LoopVersioning::addPHINodes(
if (!PN) {
PN = PHINode::Create(Inst->getType(), 2, Inst->getName() + ".lver",
&PHIBlock->front());
for (auto *User : Inst->users())
if (!VersionedLoop->contains(cast<Instruction>(User)->getParent()))
User->replaceUsesOfWith(Inst, PN);
SmallVector<User*, 8> UsersToUpdate;
for (User *U : Inst->users())
if (!VersionedLoop->contains(cast<Instruction>(U)->getParent()))
UsersToUpdate.push_back(U);
for (User *U : UsersToUpdate)
U->replaceUsesOfWith(Inst, PN);
PN->addIncoming(Inst, VersionedLoop->getExitingBlock());
}
}

65
llvm/test/Transforms/LoopVersioning/add-phi-update-users.ll Normal file
View File

@ -0,0 +1,65 @@
; RUN: opt < %s -loop-versioning -S -o - | FileCheck %s
; This test case used to end like this:
;
; Instruction does not dominate all uses!
; %t2 = load i16, i16* @b, align 1, !tbaa !2, !alias.scope !6
; %tobool = icmp eq i16 %t2, 0
; LLVM ERROR: Broken function found, compilation aborted!
;
; due to a fault where we did not replace the use of %t2 in the icmp in
; for.end, when adding a new PHI node for the versioned loops based on the
; loop-defined values used outside of the loop.
;
; Verify that the code compiles, that we get a versioned loop, and that the
; uses of %t2 in for.end and if.then are updated to use the value from the
; added phi node.
; CHECK: define void @f1
; CHECK: for.end:
; CHECK-NEXT: %t2.lver = phi i16 [ %t2, %for.body ], [ %t2.lver.orig, %for.body.lver.orig ]
; CHECK-NEXT: %tobool = icmp eq i16 %t2.lver, 0
; CHECK: if.then:
; CHECK-NEXT: store i16 %t2.lver
@a = dso_local global i16 0, align 1
@b = dso_local global i16 0, align 1
@c = dso_local global i16* null, align 1
define void @f1() {
entry:
%t0 = load i16*, i16** @c, align 1
br label %for.cond
for.cond: ; preds = %for.cond.backedge, %entry
br label %for.body
for.body: ; preds = %for.cond, %for.body
%t1 = phi i64 [ 0, %for.cond ], [ %inc, %for.body ]
%t2 = load i16, i16* @b, align 1, !tbaa !2
store i16 %t2, i16* %t0, align 1, !tbaa !2
%inc = add nuw nsw i64 %t1, 1
%cmp = icmp ult i64 %inc, 3
br i1 %cmp, label %for.body, label %for.end
for.end: ; preds = %for.body
%tobool = icmp eq i16 %t2, 0
br i1 %tobool, label %for.cond.backedge, label %if.then
for.cond.backedge: ; preds = %for.end, %if.then
br label %for.cond
if.then: ; preds = %for.end
store i16 %t2, i16* @a, align 1, !tbaa !2
br label %for.cond.backedge
}
!llvm.module.flags = !{!0}
!llvm.ident = !{!1}
!0 = !{i32 1, !"wchar_size", i32 1}
!1 = !{!"clang version 7.0.0"}
!2 = !{!3, !3, i64 0}
!3 = !{!"long long", !4, i64 0}
!4 = !{!"omnipotent char", !5, i64 0}
!5 = !{!"Simple C/C++ TBAA"}