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.

llvm-svn: 122695

2 files changed, 55 insertions, 15 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopSimplify.cpp b/llvm/lib/Transforms/Utils/LoopSimplify.cpp
index f77a58300f4..2e5b1136586 100644
--- a/llvm/lib/Transforms/Utils/LoopSimplify.cpp
+++ b/llvm/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/llvm/test/Transforms/LoopSimplify/2010-12-26-PHIInfiniteLoop.ll b/llvm/test/Transforms/LoopSimplify/2010-12-26-PHIInfiniteLoop.ll
new file mode 100644
index 00000000000..4973d43b451
--- /dev/null
+++ b/llvm/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