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[LoopReroll] Fix reroll root legality checking. 

The code checked that the first root was an appropriate distance from
the base value, but skipped checking the other roots. This could lead to
rerolling a loop that can't be legally rerolled (at least, not without
rewriting the loop in a non-trivial way).

Differential Revision: https://reviews.llvm.org/D56812

llvm-svn: 353779
This commit is contained in:
Eli Friedman 2019-02-12 00:33:25 +00:00
parent 9d0c5f9953
commit 806136f8ef
2 changed files with 34 additions and 0 deletions
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10
llvm/lib/Transforms/Scalar/LoopRerollPass.cpp
View File

@ -891,12 +891,22 @@ bool LoopReroll::DAGRootTracker::validateRootSet(DAGRootSet &DRS) {
const auto *ADR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(DRS.BaseInst));
if (!ADR)
return false;
// Check that the first root is evenly spaced.
unsigned N = DRS.Roots.size() + 1;
const SCEV *StepSCEV = SE->getMinusSCEV(SE->getSCEV(DRS.Roots[0]), ADR);
const SCEV *ScaleSCEV = SE->getConstant(StepSCEV->getType(), N);
if (ADR->getStepRecurrence(*SE) != SE->getMulExpr(StepSCEV, ScaleSCEV))
return false;
// Check that the remainling roots are evenly spaced.
for (unsigned i = 1; i < N - 1; ++i) {
const SCEV *NewStepSCEV = SE->getMinusSCEV(SE->getSCEV(DRS.Roots[i]),
SE->getSCEV(DRS.Roots[i-1]));
if (NewStepSCEV != StepSCEV)
return false;
}
return true;
}

24
llvm/test/Transforms/LoopReroll/basic.ll
View File

@ -785,6 +785,30 @@ bb19: ; preds = %bb3
ret void
}
define void @bad_step(i32* nocapture readnone %x) #0 {
entry:
br label %for.body
for.body: ; preds = %for.body, %entry
%i.08 = phi i32 [ 0, %entry ], [ %add3, %for.body ]
%call = tail call i32 @foo(i32 %i.08) #1
%add = add nsw i32 %i.08, 2
%call1 = tail call i32 @foo(i32 %add) #1
%add2 = add nsw i32 %i.08, 3
%call3 = tail call i32 @foo(i32 %add2) #1
%add3 = add nsw i32 %i.08, 6
%exitcond = icmp sge i32 %add3, 500
br i1 %exitcond, label %for.end, label %for.body
; CHECK-LABEL: @bad_step
; CHECK: %add = add nsw i32 %i.08, 2
; CHECK: %add2 = add nsw i32 %i.08, 3
; CHECK: %add3 = add nsw i32 %i.08, 6
for.end: ; preds = %for.body
ret void
}
attributes #0 = { nounwind uwtable }
attributes #1 = { nounwind }