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[LoopNest] Use `getUniqueSuccessor()` instead when checking empty blocks 

Blocks that contain only a single branch instruction to the next block can be skipped in analyzing the loop-nest structure.
This is currently done by `getSingleSuccessor()`.
However, the branch instruction might have multiple targets which happen to all be the same.
In this case, the block should still be considered as empty and skipped.

An example is `test/Transforms/LoopInterchange/update-condbranch-duplicate-successors.ll` (the LIT test for this patch is modified from it as well).

Reviewed By: Whitney

Differential Revision: https://reviews.llvm.org/D97286
This commit is contained in:
Ta-Wei Tu 2021-02-24 09:52:46 +08:00
parent 56d228a14e
commit 98c6110d9b
2 changed files with 47 additions and 3 deletions
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6
llvm/lib/Analysis/LoopNestAnalysis.cpp
View File

@ -210,7 +210,7 @@ const BasicBlock &LoopNest::skipEmptyBlockUntil(const BasicBlock *From,
assert(From && "Expecting valid From");
assert(End && "Expecting valid End");
if (From == End || !From->getSingleSuccessor())
if (From == End || !From->getUniqueSuccessor())
return *From;
auto IsEmpty = [](const BasicBlock *BB) {
@ -219,12 +219,12 @@ const BasicBlock &LoopNest::skipEmptyBlockUntil(const BasicBlock *From,
// Visited is used to avoid running into an infinite loop.
SmallPtrSet<const BasicBlock *, 4> Visited;
const BasicBlock *BB = From->getSingleSuccessor();
const BasicBlock *BB = From->getUniqueSuccessor();
const BasicBlock *PredBB = BB;
while (BB && BB != End && IsEmpty(BB) && !Visited.count(BB)) {
Visited.insert(BB);
PredBB = BB;
BB = BB->getSingleSuccessor();
BB = BB->getUniqueSuccessor();
}
return (BB == End) ? *End : *PredBB;

44
llvm/test/Analysis/LoopNestAnalysis/duplicate-successors.ll Normal file
View File

@ -0,0 +1,44 @@
; RUN: opt -passes='print<loopnest>' %s 2>&1 | FileCheck %s
@global = external dso_local global [1000 x [1000 x i32]], align 16
; CHECK: IsPerfect=true, Depth=1, OutermostLoop: inner.header, Loops: ( inner.header )
; CHECK-NEXT: IsPerfect=true, Depth=2, OutermostLoop: outer.header, Loops: ( outer.header inner.header )
define void @foo1(i1 %cmp) {
entry:
br i1 %cmp, label %bb1, label %bb1
bb1: ; preds = %entry, %entry
br i1 %cmp, label %outer.header.preheader, label %outer.header.preheader
outer.header.preheader: ; preds = %bb1, %bb1
br label %outer.header
outer.header: ; preds = %outer.header.preheader, %outer.latch
%outer.iv = phi i64 [ %outer.iv.next, %outer.latch ], [ 0, %outer.header.preheader ]
br i1 %cmp, label %inner.header.preheader, label %inner.header.preheader
inner.header.preheader: ; preds = %outer.header, %outer.header
br label %inner.header
inner.header: ; preds = %inner.header.preheader, %inner.header
%inner.iv = phi i64 [ %inner.iv.next, %inner.header ], [ 5, %inner.header.preheader ]
%ptr = getelementptr inbounds [1000 x [1000 x i32]], [1000 x [1000 x i32]]* @global, i64 0, i64 %inner.iv, i64 %outer.iv
%lv = load i32, i32* %ptr, align 4
%v = mul i32 %lv, 100
store i32 %v, i32* %ptr, align 4
%inner.iv.next = add nsw i64 %inner.iv, 1
%cond1 = icmp eq i64 %inner.iv.next, 1000
br i1 %cond1, label %outer.latch, label %inner.header
outer.latch: ; preds = %inner.header
%outer.iv.next = add nuw nsw i64 %outer.iv, 1
%cond2 = icmp eq i64 %outer.iv.next, 1000
br i1 %cond2, label %bb9, label %outer.header
bb9: ; preds = %outer.latch
br label %bb10
bb10: ; preds = %bb9
ret void
}