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[LoopInterchange] Fix interchanging contents of preheader BBs 

Summary:
Previously LCSSA was getting broken by placing instructions into the
(newly) inner *header* instead of the *pre*header.

Fixes PR43474

Reviewers: fhahn

Reviewed By: fhahn

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D75943
This commit is contained in:
Alexey Zhikhartsev 2020-03-13 15:15:11 -04:00 committed by Jimmy Zhongduo Lin
parent bb8622094d
commit f71abec661
2 changed files with 134 additions and 22 deletions
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53
llvm/lib/Transforms/Scalar/LoopInterchange.cpp
View File

@ -412,7 +412,6 @@ public:
private: private:
bool adjustLoopLinks(); bool adjustLoopLinks();
void adjustLoopPreheaders();
bool adjustLoopBranches(); bool adjustLoopBranches();
Loop *OuterLoop; Loop *OuterLoop;
@ -580,6 +579,12 @@ struct LoopInterchange : public LoopPass {
LIT.transform(); LIT.transform();
LLVM_DEBUG(dbgs() << "Loops interchanged.\n"); LLVM_DEBUG(dbgs() << "Loops interchanged.\n");
LoopsInterchanged++; LoopsInterchanged++;
assert(InnerLoop->isLCSSAForm(*DT) &&
"Inner loop not left in LCSSA form after loop interchange!");
assert(OuterLoop->isLCSSAForm(*DT) &&
"Outer loop not left in LCSSA form after loop interchange!");
return true; return true;
} }
}; };
@ -1319,6 +1324,23 @@ static void moveBBContents(BasicBlock *FromBB, Instruction *InsertBefore) {
FromBB->getTerminator()->getIterator()); FromBB->getTerminator()->getIterator());
} }
/// Swap instructions between \p BB1 and \p BB2 but keep terminators intact.
static void swapBBContents(BasicBlock *BB1, BasicBlock *BB2) {
// Save all non-terminator instructions of BB1 into TempInstrs and unlink them
// from BB1 afterwards.
auto Iter = map_range(*BB1, [](Instruction &I) { return &I; });
SmallVector<Instruction *, 4> TempInstrs(Iter.begin(), std::prev(Iter.end()));
for (Instruction *I : TempInstrs)
I->removeFromParent();
// Move instructions from BB2 to BB1.
moveBBContents(BB2, BB1->getTerminator());
// Move instructions from TempInstrs to BB2.
for (Instruction *I : TempInstrs)
I->insertBefore(BB2->getTerminator());
}
// Update BI to jump to NewBB instead of OldBB. Records updates to the // Update BI to jump to NewBB instead of OldBB. Records updates to the
// dominator tree in DTUpdates. If \p MustUpdateOnce is true, assert that // dominator tree in DTUpdates. If \p MustUpdateOnce is true, assert that
// \p OldBB is exactly once in BI's successor list. // \p OldBB is exactly once in BI's successor list.
@ -1578,30 +1600,17 @@ bool LoopInterchangeTransform::adjustLoopBranches() {
return true; return true;
} }
void LoopInterchangeTransform::adjustLoopPreheaders() {
// We have interchanged the preheaders so we need to interchange the data in
// the preheader as well.
// This is because the content of inner preheader was previously executed
// inside the outer loop.
BasicBlock *OuterLoopPreHeader = OuterLoop->getLoopPreheader();
BasicBlock *InnerLoopPreHeader = InnerLoop->getLoopPreheader();
BasicBlock *OuterLoopHeader = OuterLoop->getHeader();
BranchInst *InnerTermBI =
cast<BranchInst>(InnerLoopPreHeader->getTerminator());
// These instructions should now be executed inside the loop.
// Move instruction into a new block after outer header.
moveBBContents(InnerLoopPreHeader, OuterLoopHeader->getTerminator());
// These instructions were not executed previously in the loop so move them to
// the older inner loop preheader.
moveBBContents(OuterLoopPreHeader, InnerTermBI);
}
bool LoopInterchangeTransform::adjustLoopLinks() { bool LoopInterchangeTransform::adjustLoopLinks() {
// Adjust all branches in the inner and outer loop. // Adjust all branches in the inner and outer loop.
bool Changed = adjustLoopBranches(); bool Changed = adjustLoopBranches();
if (Changed) if (Changed) {
adjustLoopPreheaders(); // We have interchanged the preheaders so we need to interchange the data in
// the preheaders as well. This is because the content of the inner
// preheader was previously executed inside the outer loop.
BasicBlock *OuterLoopPreHeader = OuterLoop->getLoopPreheader();
BasicBlock *InnerLoopPreHeader = InnerLoop->getLoopPreheader();
swapBBContents(OuterLoopPreHeader, InnerLoopPreHeader);
}
return Changed; return Changed;
} }

103
llvm/test/Transforms/LoopInterchange/lcssa-preheader.ll Normal file
View File

@ -0,0 +1,103 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
; RUN: opt < %s -basicaa -loop-interchange -pass-remarks-missed='loop-interchange' -verify-loop-lcssa -S | FileCheck %s
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
; void foo(int n, int m) {
; int temp[16][16];
; int res[16][16];
; for(int i = 0; i < n; i++) {
; for(int j = 0; j < m; j++)
; res[j][i] = temp[j][i];
; }
; }
define void @lcssa_08(i32 %n, i32 %m) {
; CHECK-LABEL: @lcssa_08(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[TEMP:%.*]] = alloca [16 x [16 x i32]], align 4
; CHECK-NEXT: [[RES:%.*]] = alloca [16 x [16 x i32]], align 4
; CHECK-NEXT: [[CMP24:%.*]] = icmp sgt i32 [[N:%.*]], 0
; CHECK-NEXT: br i1 [[CMP24]], label [[INNER_PREHEADER:%.*]], label [[FOR_COND_CLEANUP:%.*]]
; CHECK: outer.preheader:
; CHECK-NEXT: [[WIDE_TRIP_COUNT:%.*]] = zext i32 [[M:%.*]] to i64
; CHECK-NEXT: br label [[OUTER_HEADER:%.*]]
; CHECK: outer.header:
; CHECK-NEXT: [[INDVARS_IV27:%.*]] = phi i64 [ 0, [[OUTER_PREHEADER:%.*]] ], [ [[INDVARS_IV_NEXT28:%.*]], [[OUTER_LATCH:%.*]] ]
; CHECK-NEXT: [[CMP222:%.*]] = icmp sgt i32 [[M]], 0
; CHECK-NEXT: br i1 [[CMP222]], label [[INNER_FOR_BODY_SPLIT1:%.*]], label [[OUTER_CRIT_EDGE:%.*]]
; CHECK: inner.preheader:
; CHECK-NEXT: [[WIDE_TRIP_COUNT29:%.*]] = zext i32 [[N]] to i64
; CHECK-NEXT: br label [[INNER_FOR_BODY:%.*]]
; CHECK: inner.for.body:
; CHECK-NEXT: [[INDVARS_IV:%.*]] = phi i64 [ 0, [[INNER_PREHEADER]] ], [ [[TMP1:%.*]], [[INNER_FOR_BODY_SPLIT:%.*]] ]
; CHECK-NEXT: br label [[OUTER_PREHEADER]]
; CHECK: inner.for.body.split1:
; CHECK-NEXT: [[ARRAYIDX6:%.*]] = getelementptr inbounds [16 x [16 x i32]], [16 x [16 x i32]]* [[TEMP]], i64 0, i64 [[INDVARS_IV]], i64 [[INDVARS_IV27]]
; CHECK-NEXT: [[TMP0:%.*]] = load i32, i32* [[ARRAYIDX6]], align 4
; CHECK-NEXT: [[ARRAYIDX8:%.*]] = getelementptr inbounds [16 x [16 x i32]], [16 x [16 x i32]]* [[RES]], i64 0, i64 [[INDVARS_IV]], i64 [[INDVARS_IV27]]
; CHECK-NEXT: store i32 [[TMP0]], i32* [[ARRAYIDX8]], align 4
; CHECK-NEXT: [[INDVARS_IV_NEXT:%.*]] = add nuw nsw i64 [[INDVARS_IV]], 1
; CHECK-NEXT: [[EXITCOND:%.*]] = icmp ne i64 [[INDVARS_IV_NEXT]], [[WIDE_TRIP_COUNT]]
; CHECK-NEXT: br label [[INNER_CRIT_EDGE:%.*]]
; CHECK: inner.for.body.split:
; CHECK-NEXT: [[TMP1]] = add nuw nsw i64 [[INDVARS_IV]], 1
; CHECK-NEXT: [[TMP2:%.*]] = icmp ne i64 [[TMP1]], [[WIDE_TRIP_COUNT]]
; CHECK-NEXT: br i1 [[TMP2]], label [[INNER_FOR_BODY]], label [[OUTER_CRIT_EDGE]]
; CHECK: inner.crit_edge:
; CHECK-NEXT: br label [[OUTER_LATCH]]
; CHECK: outer.latch:
; CHECK-NEXT: [[INDVARS_IV_NEXT28]] = add nuw nsw i64 [[INDVARS_IV27]], 1
; CHECK-NEXT: [[EXITCOND30:%.*]] = icmp ne i64 [[INDVARS_IV_NEXT28]], [[WIDE_TRIP_COUNT29]]
; CHECK-NEXT: br i1 [[EXITCOND30]], label [[OUTER_HEADER]], label [[INNER_FOR_BODY_SPLIT]]
; CHECK: outer.crit_edge:
; CHECK-NEXT: br label [[FOR_COND_CLEANUP]]
; CHECK: for.cond.cleanup:
; CHECK-NEXT: ret void
;
entry:
%temp = alloca [16 x [16 x i32]], align 4
%res = alloca [16 x [16 x i32]], align 4
%cmp24 = icmp sgt i32 %n, 0
br i1 %cmp24, label %outer.preheader, label %for.cond.cleanup
outer.preheader: ; preds = %entry
%wide.trip.count29 = zext i32 %n to i64
br label %outer.header
outer.header: ; preds = %outer.preheader, %outer.latch
%indvars.iv27 = phi i64 [ 0, %outer.preheader ], [ %indvars.iv.next28, %outer.latch ]
%cmp222 = icmp sgt i32 %m, 0
br i1 %cmp222, label %inner.preheader, label %outer.latch
inner.preheader: ; preds = %outer.header
; When inner.preheader becomes the outer preheader, do not move
; %wide.trip.count into the inner loop header lest LCSSA break
; (if %wide.trip.count gets moved, its use is now outside the inner loop).
%wide.trip.count = zext i32 %m to i64
br label %inner.for.body
inner.for.body: ; preds = %inner.preheader, %inner.for.body
%indvars.iv = phi i64 [ 0, %inner.preheader ], [ %indvars.iv.next, %inner.for.body ]
%arrayidx6 = getelementptr inbounds [16 x [16 x i32]], [16 x [16 x i32]]* %temp, i64 0, i64 %indvars.iv, i64 %indvars.iv27
%0 = load i32, i32* %arrayidx6, align 4
%arrayidx8 = getelementptr inbounds [16 x [16 x i32]], [16 x [16 x i32]]* %res, i64 0, i64 %indvars.iv, i64 %indvars.iv27
store i32 %0, i32* %arrayidx8, align 4
%indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
%exitcond = icmp ne i64 %indvars.iv.next, %wide.trip.count
br i1 %exitcond, label %inner.for.body, label %inner.crit_edge
inner.crit_edge: ; preds = %inner.for.body
br label %outer.latch
outer.latch: ; preds = %inner.crit_edge, %outer.header
%indvars.iv.next28 = add nuw nsw i64 %indvars.iv27, 1
%exitcond30 = icmp ne i64 %indvars.iv.next28, %wide.trip.count29
br i1 %exitcond30, label %outer.header, label %outer.crit_edge
outer.crit_edge: ; preds = %outer.latch
br label %for.cond.cleanup
for.cond.cleanup: ; preds = %outer.crit_edge, %entry
ret void
}