From 67fb341f8b0a72ca0da8ce53baa3f335c1310a85 Mon Sep 17 00:00:00 2001
From: Duncan Sands <baldrick@free.fr>
Date: Sun, 2 Jan 2011 13:38:21 +0000
Subject: [PATCH] Fix PR8702 by not having LoopSimplify claim to preserve LCSSA
 form.  As described in the PR, the pass could break LCSSA form when inserting
 preheaders.  It probably would be easy enough to fix this, but since
 currently we always go into LCSSA form after running this pass, doing so is
 not urgent.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122695 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Utils/LoopSimplify.cpp         | 27 ++++++------
 .../2010-12-26-PHIInfiniteLoop.ll             | 43 +++++++++++++++++++
 2 files changed, 55 insertions(+), 15 deletions(-)
 create mode 100644 test/Transforms/LoopSimplify/2010-12-26-PHIInfiniteLoop.ll

diff --git a/lib/Transforms/Utils/LoopSimplify.cpp b/lib/Transforms/Utils/LoopSimplify.cpp
index f77a58300f4..2e5b1136586 100644
--- a/lib/Transforms/Utils/LoopSimplify.cpp
+++ b/lib/Transforms/Utils/LoopSimplify.cpp
@@ -91,7 +91,6 @@ namespace {
       AU.addPreserved<ScalarEvolution>();
       AU.addPreservedID(BreakCriticalEdgesID);  // No critical edges added.
       AU.addPreserved<DominanceFrontier>();
-      AU.addPreservedID(LCSSAID);
     }
 
     /// verifyAnalysis() - Verify LoopSimplifyForm's guarantees.
@@ -269,12 +268,11 @@ ReprocessLoop:
   PHINode *PN;
   for (BasicBlock::iterator I = L->getHeader()->begin();
        (PN = dyn_cast<PHINode>(I++)); )
-    if (Value *V = SimplifyInstruction(PN, 0, DT))
-      if (LI->replacementPreservesLCSSAForm(PN, V)) {
-          if (AA) AA->deleteValue(PN);
-          PN->replaceAllUsesWith(V);
-          PN->eraseFromParent();
-      }
+    if (Value *V = SimplifyInstruction(PN, 0, DT)) {
+      if (AA) AA->deleteValue(PN);
+      PN->replaceAllUsesWith(V);
+      PN->eraseFromParent();
+    }
 
   // If this loop has multiple exits and the exits all go to the same
   // block, attempt to merge the exits. This helps several passes, such
@@ -450,14 +448,13 @@ static PHINode *FindPHIToPartitionLoops(Loop *L, DominatorTree *DT,
   for (BasicBlock::iterator I = L->getHeader()->begin(); isa<PHINode>(I); ) {
     PHINode *PN = cast<PHINode>(I);
     ++I;
-    if (Value *V = SimplifyInstruction(PN, 0, DT))
-      if (LI->replacementPreservesLCSSAForm(PN, V)) {
-        // This is a degenerate PHI already, don't modify it!
-        PN->replaceAllUsesWith(V);
-        if (AA) AA->deleteValue(PN);
-        PN->eraseFromParent();
-        continue;
-      }
+    if (Value *V = SimplifyInstruction(PN, 0, DT)) {
+      // This is a degenerate PHI already, don't modify it!
+      PN->replaceAllUsesWith(V);
+      if (AA) AA->deleteValue(PN);
+      PN->eraseFromParent();
+      continue;
+    }
 
     // Scan this PHI node looking for a use of the PHI node by itself.
     for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
diff --git a/test/Transforms/LoopSimplify/2010-12-26-PHIInfiniteLoop.ll b/test/Transforms/LoopSimplify/2010-12-26-PHIInfiniteLoop.ll
new file mode 100644
index 00000000000..4973d43b451
--- /dev/null
+++ b/test/Transforms/LoopSimplify/2010-12-26-PHIInfiniteLoop.ll
@@ -0,0 +1,43 @@
+; RUN: opt < %s -loopsimplify -S
+; PR8702
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64"
+target triple = "x86_64-unknown-freebsd9.0"
+
+declare void @foo(i32 %x)
+
+define fastcc void @inm_merge() nounwind {
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %while.cond36.i, %entry
+  br i1 undef, label %do.body, label %for.body
+
+for.body:                                         ; preds = %for.cond
+  br i1 undef, label %while.cond36.i, label %if.end44
+
+if.end44:                                         ; preds = %for.body
+  %call49 = call fastcc i32 @inm_get_source()
+  br i1 undef, label %if.end54, label %for.cond64
+
+if.end54:                                         ; preds = %if.end44
+  br label %while.cond36.i
+
+while.cond36.i:                                   ; preds = %if.end54, %for.body
+  br label %for.cond
+
+for.cond64:                                       ; preds = %if.end88, %for.cond64, %if.end44
+  %error.161 = phi i32 [ %error.161, %for.cond64 ], [ %error.161, %if.end88 ], [ %call49, %if.end44 ]
+  call void @foo(i32 %error.161)
+  br i1 undef, label %for.cond64, label %if.end88
+
+if.end88:                                         ; preds = %for.cond64
+  br i1 undef, label %for.cond64, label %if.end98
+
+if.end98:                                         ; preds = %if.end88
+  unreachable
+
+do.body:                                          ; preds = %for.cond
+  unreachable
+}
+
+declare fastcc i32 @inm_get_source() nounwind