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Handle successor's PHI node correctly when flattening CFG merges two if-regions

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Summary:
FlattenCFG merges two 'if' basicblocks by inserting one basicblock
to another basicblock. The inserted basicblock can have a successor
that contains a PHI node whoes incoming basicblock is the inserted
basicblock. Since the existing code does not handle it, it becomes
a badref.

if (cond1)
  statement
if (cond2)
  statement
successor - contains PHI node whose predecessor is cond2

-->
if (cond1 || cond2)
  statement
(BB for cond2 was deleted)
successor - contains PHI node whose predecessor is cond2 --> bad ref!

Author: Jaebaek Seo

Reviewers: asbirlea, kuhar, tstellar, chandlerc, davide, dexonsmith

Reviewed By: kuhar

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D68032

llvm-svn: 372989
This commit is contained in:
Jakub Kuderski 2019-09-26 15:20:17 +00:00
parent 0129f9ebba
commit cc245c26cb
2 changed files with 41 additions and 1 deletions
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12
lib/Transforms/Utils/FlattenCFG.cpp
View File

@ -67,7 +67,7 @@ public:
/// Before:
/// ......
/// %cmp10 = fcmp une float %tmp1, %tmp2
/// br i1 %cmp1, label %if.then, label %lor.rhs
/// br i1 %cmp10, label %if.then, label %lor.rhs
///
/// lor.rhs:
/// ......
@ -453,6 +453,16 @@ bool FlattenCFGOpt::MergeIfRegion(BasicBlock *BB, IRBuilder<> &Builder) {
PBI->replaceUsesOfWith(CC, NC);
Builder.SetInsertPoint(SaveInsertBB, SaveInsertPt);
// Handle PHI node to replace its predecessors to FirstEntryBlock.
for (BasicBlock *Succ : successors(PBI)) {
for (PHINode &Phi : Succ->phis()) {
for (unsigned i = 0, e = Phi.getNumIncomingValues(); i != e; ++i) {
if (Phi.getIncomingBlock(i) == SecondEntryBlock)
Phi.setIncomingBlock(i, FirstEntryBlock);
}
}
}
// Remove IfTrue1
if (IfTrue1 != FirstEntryBlock) {
IfTrue1->dropAllReferences();

30
test/Transforms/Util/flattencfg.ll
View File

@ -54,3 +54,33 @@ bb0: ; preds = %bb1, %entry
br i1 %1, label %bb4, label %bb3
}
; CHECK-LABEL: @test_not_crash3
; CHECK-NEXT: entry:
; CHECK-NEXT: %a_eq_0 = icmp eq i32 %a, 0
; CHECK-NEXT: %a_eq_1 = icmp eq i32 %a, 1
; CHECK-NEXT: [[COND:%[a-z0-9]+]] = or i1 %a_eq_0, %a_eq_1
; CHECK-NEXT: br i1 [[COND]], label %bb2, label %bb3
; CHECK: bb2:
; CHECK-NEXT: br label %bb3
; CHECK: bb3:
; CHECK-NEXT: %check_badref = phi i32 [ 17, %entry ], [ 11, %bb2 ]
; CHECK-NEXT: ret void
define void @test_not_crash3(i32 %a) #0 {
entry:
%a_eq_0 = icmp eq i32 %a, 0
br i1 %a_eq_0, label %bb0, label %bb1
bb0: ; preds = %entry
br label %bb1
bb1: ; preds = %bb0, %entry
%a_eq_1 = icmp eq i32 %a, 1
br i1 %a_eq_1, label %bb2, label %bb3
bb2: ; preds = %bb1
br label %bb3
bb3: ; preds = %bb2, %bb1
%check_badref = phi i32 [ 17, %bb1 ], [ 11, %bb2 ]
ret void
}