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[SCEV] Don't create SCEV expressions that break LCSSA

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Prevent `createNodeFromSelectLikePHI` from creating SCEV expressions
that break LCSSA.

A better fix for the same issue is to teach SCEVExpander to not break
LCSSA by inserting PHI nodes at appropriate places.  That's planned for
the future.

Fixes PR25360.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251756 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sanjoy Das 2015-10-31 23:21:40 +00:00
parent 861933b54e
commit 2b19a08110
3 changed files with 62 additions and 0 deletions
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5
lib/Analysis/ScalarEvolution.cpp
View File

@ -3943,6 +3943,11 @@ const SCEV *ScalarEvolution::createNodeFromSelectLikePHI(PHINode *PN) {
if (PN->getNumIncomingValues() == 2) {
const Loop *L = LI.getLoopFor(PN->getParent());
// We don't want to break LCSSA, even in a SCEV expression tree.
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
if (LI.getLoopFor(PN->getIncomingBlock(i)) != L)
return nullptr;
// Try to match
//
// br %cond, label %left, label %right

24
test/Analysis/ScalarEvolution/smax-br-phi-idioms.ll
View File

@ -102,3 +102,27 @@ define i32 @f4(i32 %x, i32 %init, i32 %lim) {
; CHECK-NEXT: --> %v U: full-set S: full-set
ret i32 %v
}
define i32 @f5(i32* %val) {
; CHECK-LABEL: Classifying expressions for: @f5
entry:
br label %for.end
for.condt:
br i1 true, label %for.cond.0, label %for.end
for.end:
%inc = load i32, i32* %val
br i1 false, label %for.condt, label %for.cond.0
for.cond.0:
%init = phi i32 [ 0, %for.condt ], [ %inc, %for.end ]
; CHECK: %init = phi i32 [ 0, %for.condt ], [ %inc, %for.end ]
; CHECK-NEXT: --> %init U: full-set S: full-set
; Matching "through" %init will break LCSSA at the SCEV expression
; level.
ret i32 %init
}

33
test/Transforms/IndVarSimplify/pr25360.ll Normal file
View File

@ -0,0 +1,33 @@
; RUN: opt -indvars -S < %s | FileCheck %s
; Ensure that does not crash
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
define void @f() {
; CHECK-LABEL: @f(
entry:
br label %for.end
for.condt: ; preds = %for.end
br i1 true, label %for.cond.0, label %for.end
for.end: ; preds = %for.body.3
%inc = select i1 undef, i32 2, i32 1
br i1 false, label %for.condt, label %for.cond.0
for.cond.0: ; preds = %for.end, %for.condt
%init = phi i32 [ 0, %for.condt ], [ %inc, %for.end ]
br i1 true, label %for.end.13, label %for.body.9
for.body.9: ; preds = %for.body.9, %for.cond.0
%p1.addr.22 = phi i32 [ %inc10, %for.body.9 ], [ %init, %for.cond.0 ]
%inc10 = add i32 %p1.addr.22, 1
br i1 true, label %for.end.13, label %for.body.9
for.end.13: ; preds = %for.cond.7.for.end.13_crit_edge, %for.cond.0
%p1.addr.2.lcssa = phi i32 [ %inc10, %for.body.9 ], [ %init, %for.cond.0 ]
ret void
}