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[LoopInterchange] Check phis in all subloops 

This is the bugfix to the miscompile mentioned in
https://reviews.llvm.org/D132055#3814831. The IR
that reproduced the bug is added as the test case in
this patch.

What this patch does is that, during legality phase
instead of checking the phi nodes only in `InnerLoop`
and `OuterLoop`, we check phi nodes in all subloops
of the `OuterLoop`. Suppose if the loop nest is triply
nested, and `InnerLoop` and `OuterLoop` is the middle
loop and the outermost loop respectively, we'll check
phi nodes in the innermost loop as well, in addition to
the ones in the middle and outermost loops.

Reviewed By: Meinersbur, #loopoptwg

Differential Revision: https://reviews.llvm.org/D134930
This commit is contained in:
Congzhe Cao 2022-11-04 00:07:42 -04:00 committed by CongzheUalberta
parent e419620fc2
commit 75b33d6bd5
2 changed files with 97 additions and 12 deletions
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32
llvm/lib/Transforms/Scalar/LoopInterchange.cpp
View File

@ -831,18 +831,26 @@ bool LoopInterchangeLegality::currentLimitations() {
}
Inductions.clear();
if (!findInductionAndReductions(InnerLoop, Inductions, nullptr)) {
LLVM_DEBUG(
dbgs() << "Only inner loops with induction or reduction PHI nodes "
<< "are supported currently.\n");
ORE->emit([&]() {
return OptimizationRemarkMissed(DEBUG_TYPE, "UnsupportedPHIInner",
InnerLoop->getStartLoc(),
InnerLoop->getHeader())
<< "Only inner loops with induction or reduction PHI nodes can be"
" interchange currently.";
});
return true;
// For multi-level loop nests, make sure that all phi nodes for inner loops
// at all levels can be recognized as a induction or reduction phi. Bail out
// if a phi node at a certain nesting level cannot be properly recognized.
Loop *CurLevelLoop = OuterLoop;
while (!CurLevelLoop->getSubLoops().empty()) {
// We already made sure that the loop nest is tightly nested.
CurLevelLoop = CurLevelLoop->getSubLoops().front();
if (!findInductionAndReductions(CurLevelLoop, Inductions, nullptr)) {
LLVM_DEBUG(
dbgs() << "Only inner loops with induction or reduction PHI nodes "
<< "are supported currently.\n");
ORE->emit([&]() {
return OptimizationRemarkMissed(DEBUG_TYPE, "UnsupportedPHIInner",
CurLevelLoop->getStartLoc(),
CurLevelLoop->getHeader())
<< "Only inner loops with induction or reduction PHI nodes can be"
" interchange currently.";
});
return true;
}
}
// TODO: Triangular loops are not handled for now.

77
llvm/test/Transforms/LoopInterchange/multilevel-partial-reduction.ll Normal file
View File

@ -0,0 +1,77 @@
; RUN: opt < %s -loop-interchange -cache-line-size=4 -pass-remarks-missed='loop-interchange' -pass-remarks-output=%t -S \
; RUN: -verify-dom-info -verify-loop-info -verify-loop-lcssa
; RUN: FileCheck --input-file=%t --check-prefix=REMARKS %s
@b = external global [512 x [4 x i32]]
@c = global [2 x [4 x i32]] zeroinitializer, align 1
; Check that the outermost and the middle loops are not interchanged since
; the innermost loop has a reduction operation which is however not in a form
; that loop interchange can handle. Interchanging the outermost and the
; middle loops would intervene with the reduction and cause miscompile.
; REMARKS: --- !Missed
; REMARKS-NEXT: Pass: loop-interchange
; REMARKS-NEXT: Name: UnsupportedPHIInner
; REMARKS-NEXT: Function: test7
; REMARKS: --- !Missed
; REMARKS-NEXT: Pass: loop-interchange
; REMARKS-NEXT: Name: UnsupportedPHIInner
; REMARKS-NEXT: Function: test7
define i32 @test7() {
entry:
br label %for.cond1.preheader.i
for.cond1.preheader.i: ; preds = %for.inc19.i, %entry
%i.011.i = phi i16 [ 0, %entry ], [ %inc20.i, %for.inc19.i ]
br label %for.cond4.preheader.i
for.cond4.preheader.i: ; preds = %middle.block, %for.cond1.preheader.i
%j.010.i = phi i16 [ 0, %for.cond1.preheader.i ], [ %inc17.i, %middle.block ]
%arrayidx14.i = getelementptr inbounds [2 x [4 x i32]], ptr @c, i16 0, i16 %i.011.i, i16 %j.010.i
%arrayidx14.promoted.i = load i32, ptr %arrayidx14.i, align 1
%0 = insertelement <4 x i32> <i32 poison, i32 0, i32 0, i32 0>, i32 %arrayidx14.promoted.i, i64 0
br label %vector.body
vector.body: ; preds = %vector.body, %for.cond4.preheader.i
%index = phi i16 [ 0, %for.cond4.preheader.i ], [ %index.next, %vector.body ]
%vec.phi = phi <4 x i32> [ %0, %for.cond4.preheader.i ], [ %16, %vector.body ]
%1 = or i16 %index, 1
%2 = or i16 %index, 2
%3 = or i16 %index, 3
%4 = getelementptr inbounds [512 x [4 x i32]], ptr @b, i16 0, i16 %index, i16 %j.010.i
%5 = getelementptr inbounds [512 x [4 x i32]], ptr @b, i16 0, i16 %1, i16 %j.010.i
%6 = getelementptr inbounds [512 x [4 x i32]], ptr @b, i16 0, i16 %2, i16 %j.010.i
%7 = getelementptr inbounds [512 x [4 x i32]], ptr @b, i16 0, i16 %3, i16 %j.010.i
%8 = load i32, ptr %4, align 1
%9 = load i32, ptr %5, align 1
%10 = load i32, ptr %6, align 1
%11 = load i32, ptr %7, align 1
%12 = insertelement <4 x i32> poison, i32 %8, i64 0
%13 = insertelement <4 x i32> %12, i32 %9, i64 1
%14 = insertelement <4 x i32> %13, i32 %10, i64 2
%15 = insertelement <4 x i32> %14, i32 %11, i64 3
%16 = add <4 x i32> %15, %vec.phi
%index.next = add nuw i16 %index, 4
%17 = icmp eq i16 %index.next, 512
br i1 %17, label %middle.block, label %vector.body
middle.block: ; preds = %vector.body
%18 = tail call i32 @llvm.vector.reduce.add.v4i32(<4 x i32> %16)
store i32 %18, ptr %arrayidx14.i, align 1
%inc17.i = add nuw nsw i16 %j.010.i, 1
%exitcond12.not.i = icmp eq i16 %inc17.i, 4
br i1 %exitcond12.not.i, label %for.inc19.i, label %for.cond4.preheader.i
for.inc19.i: ; preds = %middle.block
%inc20.i = add nuw nsw i16 %i.011.i, 1
%exitcond13.not.i = icmp eq i16 %inc20.i, 2
br i1 %exitcond13.not.i, label %test.exit, label %for.cond1.preheader.i
test.exit: ; preds = %for.inc19.i
%19 = load i32, ptr @c, align 1
ret i32 %19
}
declare i32 @llvm.vector.reduce.add.v4i32(<4 x i32>)