From 872392e1a9c2787d731a83a3ec3b998da2855d86 Mon Sep 17 00:00:00 2001
From: Silviu Baranga <silviu.baranga@arm.com>
Date: Mon, 21 Mar 2016 12:44:29 +0000
Subject: [PATCH] [IndVars] Fix PR26974: make sure replaceCongruentIVs doesn't
 break LCSSA

Summary:
replaceCongruentIVs can break LCSSA when trying to replace IV increments
since it tries to replace all uses of a phi node with another phi node
while both of the phi nodes are not necessarily in the processed loop.
This will cause an assert in IndVars.

To fix this, we add a check to make sure that the replacement maintains
LCSSA.

Reviewers: sanjoy

Subscribers: mzolotukhin, llvm-commits

Differential Revision: http://reviews.llvm.org/D18266

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@263941 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ScalarEvolutionExpander.cpp  |  1 +
 test/Transforms/IndVarSimplify/pr26974.ll | 60 +++++++++++++++++++++++
 2 files changed, 61 insertions(+)
 create mode 100644 test/Transforms/IndVarSimplify/pr26974.ll

diff --git a/lib/Analysis/ScalarEvolutionExpander.cpp b/lib/Analysis/ScalarEvolutionExpander.cpp
index d083037a90f..4db3c7fb7f9 100644
--- a/lib/Analysis/ScalarEvolutionExpander.cpp
+++ b/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -1820,6 +1820,7 @@ unsigned SCEVExpander::replaceCongruentIVs(Loop *L, const DominatorTree *DT,
                                                    IsomorphicInc->getType());
       if (OrigInc != IsomorphicInc
           && TruncExpr == SE.getSCEV(IsomorphicInc)
+          && SE.LI.replacementPreservesLCSSAForm(IsomorphicInc, OrigInc)
           && ((isa<PHINode>(OrigInc) && isa<PHINode>(IsomorphicInc))
               || hoistIVInc(OrigInc, IsomorphicInc))) {
         DEBUG_WITH_TYPE(DebugType, dbgs()
diff --git a/test/Transforms/IndVarSimplify/pr26974.ll b/test/Transforms/IndVarSimplify/pr26974.ll
new file mode 100644
index 00000000000..28a736441cd
--- /dev/null
+++ b/test/Transforms/IndVarSimplify/pr26974.ll
@@ -0,0 +1,60 @@
+; RUN: opt -indvars  -S < %s | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+
+; indvars will try to replace %b.0.lcssa with %t.1. If it does this,
+; it will break LCSSA.
+
+@c = external global i32, align 4
+
+; CHECK-LABEL: @fn1
+define void @fn1() {
+entry:
+  br label %for.body
+
+for.cond1.preheader:                              ; preds = %for.body
+  %0 = load i32, i32* @c, align 4
+  br i1 undef, label %for.cond1.us.preheader, label %for.cond1
+
+for.cond1.us.preheader:                           ; preds = %for.cond1.preheader
+  br label %for.cond1.us
+
+for.cond1.us:                                     ; preds = %for.cond1.us, %for.cond1.us.preheader
+  br label %for.cond1.us
+
+for.body:                                         ; preds = %for.body, %entry
+  br i1 undef, label %for.body, label %for.cond1.preheader
+
+for.cond1:                                        ; preds = %for.cond1.preheader
+  br i1 true, label %for.body9.lr.ph, label %for.cond13.preheader
+
+for.body9.lr.ph:                                  ; preds = %for.cond1
+  br i1 undef, label %for.body9.us.preheader, label %for.body9
+
+for.body9.us.preheader:                           ; preds = %for.body9.lr.ph
+  br label %for.body9.us
+
+for.body9.us:                                     ; preds = %for.body9.us, %for.body9.us.preheader
+  br label %for.body9.us
+
+for.cond13.preheader:                             ; preds = %for.body9, %for.cond1
+  %b.0.lcssa = phi i32 [ %0, %for.body9 ], [ 0, %for.cond1 ]
+  br label %for.cond13
+
+for.body9:                                        ; preds = %for.body9.lr.ph
+  br label %for.cond13.preheader
+
+for.cond13:                                       ; preds = %for.cond13, %for.cond13.preheader
+  %d.1 = phi i32 [ %t.1, %for.cond13 ], [ %0, %for.cond13.preheader ]
+  %t.1 = phi i32 [ %b.0.lcssa, %for.cond13 ], [ %0, %for.cond13.preheader ]
+  br i1 undef, label %for.cond18.preheader, label %for.cond13
+
+for.cond18.preheader:                             ; preds = %for.cond13
+  br label %for.cond18
+
+for.cond18:                                       ; preds = %for.cond18, %for.cond18.preheader
+  %b.1 = phi i32 [ %xor, %for.cond18 ], [ %b.0.lcssa, %for.cond18.preheader ]
+  %add = add nsw i32 %b.1, %d.1
+  %xor = xor i32 %add, %b.1
+  br label %for.cond18
+}