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Fix PR25372 - teach replaceCongruentPHIs to handle cases where SE evaluates a PHI to a SCEVConstant 

Summary:
Since now Scalar Evolution can create non-add rec expressions for PHI
nodes, it can also create SCEVConstant expressions. This will confuse
replaceCongruentPHIs, which previously relied on the fact that SCEV
could not produce constants in this case.

We will now replace the node with a constant in these cases - or avoid
processing the Phi in case of a type mismatch.

Reviewers: sanjoy

Subscribers: llvm-commits, majnemer

Differential Revision: http://reviews.llvm.org/D14230

llvm-svn: 251938
This commit is contained in:
Silviu Baranga 2015-11-03 16:27:04 +00:00
parent 2f344637d6
commit 308a7c7ed4
2 changed files with 47 additions and 1 deletions
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15
llvm/lib/Analysis/ScalarEvolutionExpander.cpp
View File

@ -1735,9 +1735,22 @@ unsigned SCEVExpander::replaceCongruentIVs(Loop *L, const DominatorTree *DT,
PEnd = Phis.end(); PIter != PEnd; ++PIter) {
PHINode *Phi = *PIter;
auto SimplifyPHINode = [&](PHINode *PN) -> Value * {
if (Value *V = SimplifyInstruction(PN, DL, &SE.TLI, &SE.DT, &SE.AC))
return V;
if (!SE.isSCEVable(PN->getType()))
return nullptr;
auto *Const = dyn_cast<SCEVConstant>(SE.getSCEV(PN));
if (!Const)
return nullptr;
return Const->getValue();
};
// Fold constant phis. They may be congruent to other constant phis and
// would confuse the logic below that expects proper IVs.
if (Value *V = SimplifyInstruction(Phi, DL, &SE.TLI, &SE.DT, &SE.AC)) {
if (Value *V = SimplifyPHINode(Phi)) {
if (V->getType() != Phi->getType())
continue;
Phi->replaceAllUsesWith(V);
DeadInsts.emplace_back(Phi);
++NumElim;

33
llvm/test/Transforms/IndVarSimplify/const_phi.ll Normal file
View File

@ -0,0 +1,33 @@
; RUN: opt < %s -indvars -S | FileCheck %s
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
; PR25372
; We can compute the expression of %phi0 and that is a SCEV
; constant. However, instcombine can't deduce this, so we can
; potentially end up trying to handle a constant when replacing
; congruent IVs.
; CHECK-LABEL: crash
define void @crash() {
entry:
br i1 false, label %not_taken, label %pre
not_taken:
br label %pre
pre:
; %phi0.pre and %phi1.pre are evaluated by SCEV to constant 0.
%phi0.pre = phi i32 [ 0, %entry ], [ 2, %not_taken ]
%phi1.pre = phi i32 [ 0, %entry ], [ 1, %not_taken ]
br label %loop
loop:
; %phi0 and %phi1 are evaluated by SCEV to constant 0.
%phi0 = phi i32 [ 0, %loop ], [ %phi0.pre, %pre ]
%phi1 = phi i32 [ 0, %loop ], [ %phi1.pre, %pre ]
br i1 undef, label %exit, label %loop
exit:
ret void
}