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[Mem2Reg] Fix nondeterministic corner case

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Summary:
When mem2reg inserts phi nodes in blocks with unreachable predecessors,
it adds undef operands for those incoming edges.  When there are
multiple such predecessors, the order is currently based on the address
of the BasicBlocks.  This change fixes that by using the BBNumbers in
the sort/search predicates, as is done elsewhere in mem2reg to ensure
determinism.

Also adds a testcase with a bunch of unreachable preds, which
(nodeterministically) fails without the fix.


Reviewers: majnemer

Reviewed By: majnemer

Subscribers: mgrang, llvm-commits

Differential Revision: https://reviews.llvm.org/D55077

llvm-svn: 348024
This commit is contained in:
Joseph Tremoulet 2018-11-30 19:20:02 +00:00
parent 6dd6c39ab9
commit 00f16af21d
2 changed files with 59 additions and 2 deletions
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8
lib/Transforms/Utils/PromoteMemoryToRegister.cpp
View File

@ -751,14 +751,18 @@ void PromoteMem2Reg::run() {
// Ok, now we know that all of the PHI nodes are missing entries for some
// basic blocks. Start by sorting the incoming predecessors for efficient
// access.
llvm::sort(Preds);
auto CompareBBNumbers = [this](BasicBlock *A, BasicBlock *B) {
return BBNumbers.lookup(A) < BBNumbers.lookup(B);
};
llvm::sort(Preds, CompareBBNumbers);
// Now we loop through all BB's which have entries in SomePHI and remove
// them from the Preds list.
for (unsigned i = 0, e = SomePHI->getNumIncomingValues(); i != e; ++i) {
// Do a log(n) search of the Preds list for the entry we want.
SmallVectorImpl<BasicBlock *>::iterator EntIt = std::lower_bound(
Preds.begin(), Preds.end(), SomePHI->getIncomingBlock(i));
Preds.begin(), Preds.end(), SomePHI->getIncomingBlock(i),
CompareBBNumbers);
assert(EntIt != Preds.end() && *EntIt == SomePHI->getIncomingBlock(i) &&
"PHI node has entry for a block which is not a predecessor!");

53
test/Transforms/Mem2Reg/undef-order.ll Normal file
View File

@ -0,0 +1,53 @@
;RUN: opt -mem2reg -S < %s | FileCheck %s
declare i1 @cond()
define i32 @foo() {
Entry:
%val = alloca i32
%c1 = call i1 @cond()
br i1 %c1, label %Store1, label %Store2
Block1:
br label %Join
Block2:
br label %Join
Block3:
br label %Join
Block4:
br label %Join
Block5:
br label %Join
Store1:
store i32 1, i32* %val
br label %Join
Block6:
br label %Join
Block7:
br label %Join
Block8:
br label %Join
Block9:
br label %Join
Block10:
br label %Join
Store2:
store i32 2, i32* %val
br label %Join
Block11:
br label %Join
Block12:
br label %Join
Block13:
br label %Join
Block14:
br label %Join
Block15:
br label %Join
Block16:
br label %Join
Join:
; Phi inserted here should have operands appended deterministically
; CHECK: %val.0 = phi i32 [ 1, %Store1 ], [ 2, %Store2 ], [ undef, %Block1 ], [ undef, %Block2 ], [ undef, %Block3 ], [ undef, %Block4 ], [ undef, %Block5 ], [ undef, %Block6 ], [ undef, %Block7 ], [ undef, %Block8 ], [ undef, %Block9 ], [ undef, %Block10 ], [ undef, %Block11 ], [ undef, %Block12 ], [ undef, %Block13 ], [ undef, %Block14 ], [ undef, %Block15 ], [ undef, %Block16 ]
%result = load i32, i32* %val
ret i32 %result
}