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Scalar: Don't visit constants in findInnerReductionPhi in LoopInterchange 

In LoopInterchange, `findInnerReductionPhi()` looks for reduction
variables, which cannot be constants. Update it to return early in that
case.

This also addresses a blocker for removing use-lists from ConstantData,
whose users could be spread across arbitrary modules in the same
LLVMContext.

Differential Revision: https://reviews.llvm.org/D94712
This commit is contained in:
Anton Rapetov 2021-01-21 12:15:31 -08:00 committed by Duncan P. N. Exon Smith
parent 8827e07aaf
commit bfec9148a0
2 changed files with 43 additions and 0 deletions
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4
llvm/lib/Transforms/Scalar/LoopInterchange.cpp
View File

@ -661,6 +661,10 @@ static Value *followLCSSA(Value *SV) {
// Check V's users to see if it is involved in a reduction in L.
static PHINode *findInnerReductionPhi(Loop *L, Value *V) {
// Reduction variables cannot be constants.
if (isa<Constant>(V))
return nullptr;
for (Value *User : V->users()) {
if (PHINode *PHI = dyn_cast<PHINode>(User)) {
if (PHI->getNumIncomingValues() == 1)

39
llvm/test/Transforms/LoopInterchange/reductions-across-inner-and-outer-loop.ll
View File

@ -150,3 +150,42 @@ for1.loopexit: ; preds = %for1.inc
%sum.inc.lcssa2 = phi i64 [ %sum.inc.lcssa, %for1.inc ]
ret i64 %sum.inc.lcssa2
}
; Check that we do not interchange or crash if the PHI in the outer loop gets a
; constant from the inner loop.
; REMARKS: --- !Missed
; REMARKS-NEXT: Pass: loop-interchange
; REMARKS-NEXT: Name: UnsupportedPHIOuter
; REMARKS-NEXT: Function: test_constant_inner_loop_res
define i64 @test_constant_inner_loop_res([100 x [100 x i64]]* %Arr) {
entry:
br label %for1.header
for1.header: ; preds = %for1.inc, %entry
%indvars.iv23 = phi i64 [ 0, %entry ], [ %indvars.iv.next24, %for1.inc ]
%sum.outer = phi i64 [ 0, %entry ], [ %sum.inc.amend, %for1.inc ]
br label %for2
for2: ; preds = %for2, %for1.header
%indvars.iv = phi i64 [ 0, %for1.header ], [ %indvars.iv.next.3, %for2 ]
%sum.inner = phi i64 [ %sum.outer, %for1.header ], [ %sum.inc, %for2 ]
%arrayidx = getelementptr inbounds [100 x [100 x i64]], [100 x [100 x i64]]* %Arr, i64 0, i64 %indvars.iv, i64 %indvars.iv23
%lv = load i64, i64* %arrayidx, align 4
%sum.inc = add i64 %sum.inner, %lv
%indvars.iv.next.3 = add nuw nsw i64 %indvars.iv, 1
%exit1 = icmp eq i64 %indvars.iv.next.3, 100
br i1 %exit1, label %for1.inc, label %for2
for1.inc: ; preds = %for2
%sum.inc.lcssa = phi i64 [ %sum.inc, %for2 ]
%const.lcssa = phi i64 [ 0, %for2 ]
%sum.inc.amend = add i64 %const.lcssa, %sum.inc.lcssa
%indvars.iv.next24 = add nuw nsw i64 %indvars.iv23, 1
%exit2 = icmp eq i64 %indvars.iv.next24, 100
br i1 %exit2, label %for1.loopexit, label %for1.header
for1.loopexit: ; preds = %for1.inc
%il.res.lcssa2 = phi i64 [ %sum.inc.amend, %for1.inc ]
ret i64 %il.res.lcssa2
}