From de53dc03f5c1549f3176e979bbeeac965dfa5cbc Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Sat, 27 Jun 2009 05:16:57 +0000
Subject: [PATCH] When a value is used multiple times within a single PHI,
 instructions inserted to replace that value must dominate all of of the basic
 blocks associated with the uses of the value in the PHI, not just one of
 them.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74376 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Scalar/IndVarSimplify.cpp      | 18 ++++++++--
 .../phi-uses-value-multiple-times.ll          | 33 +++++++++++++++++++
 2 files changed, 48 insertions(+), 3 deletions(-)
 create mode 100644 test/Transforms/IndVarSimplify/phi-uses-value-multiple-times.ll

diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp
index d2ba25637e0..27e377f9037 100644
--- a/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -70,6 +70,7 @@ namespace {
     IVUsers         *IU;
     LoopInfo        *LI;
     ScalarEvolution *SE;
+    DominatorTree   *DT;
     bool Changed;
   public:
 
@@ -329,6 +330,7 @@ bool IndVarSimplify::runOnLoop(Loop *L, LPPassManager &LPM) {
   IU = &getAnalysis<IVUsers>();
   LI = &getAnalysis<LoopInfo>();
   SE = &getAnalysis<ScalarEvolution>();
+  DT = &getAnalysis<DominatorTree>();
   Changed = false;
 
   // If there are any floating-point recurrences, attempt to
@@ -479,12 +481,22 @@ void IndVarSimplify::RewriteIVExpressions(Loop *L, const Type *LargestType,
       if (!AR->isLoopInvariant(L) && !Stride->isLoopInvariant(L))
         continue;
 
+      // Determine the insertion point for this user. By default, insert
+      // immediately before the user. The SCEVExpander class will automatically
+      // hoist loop invariants out of the loop. For PHI nodes, there may be
+      // multiple uses, so compute the nearest common dominator for the
+      // incoming blocks.
       Instruction *InsertPt = User;
       if (PHINode *PHI = dyn_cast<PHINode>(InsertPt))
-        for (unsigned i = 0; ; ++i)
+        for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
           if (PHI->getIncomingValue(i) == Op) {
-            InsertPt = PHI->getIncomingBlock(i)->getTerminator();
-            break;
+            if (InsertPt == User)
+              InsertPt = PHI->getIncomingBlock(i)->getTerminator();
+            else
+              InsertPt =
+                DT->findNearestCommonDominator(InsertPt->getParent(),
+                                               PHI->getIncomingBlock(i))
+                      ->getTerminator();
           }
 
       // Now expand it into actual Instructions and patch it into place.
diff --git a/test/Transforms/IndVarSimplify/phi-uses-value-multiple-times.ll b/test/Transforms/IndVarSimplify/phi-uses-value-multiple-times.ll
new file mode 100644
index 00000000000..7119cbbc05c
--- /dev/null
+++ b/test/Transforms/IndVarSimplify/phi-uses-value-multiple-times.ll
@@ -0,0 +1,33 @@
+; RUN: llvm-as < %s | opt -indvars
+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"
+
+@ue = external global i64
+
+define i32 @foo() nounwind {
+entry:
+	br label %bb38.i
+
+bb14.i27:
+	%t0 = load i64* @ue, align 8
+	%t1 = sub i64 %t0, %i.0.i35
+	%t2 = add i64 %t1, 1
+	br i1 undef, label %bb15.i28, label %bb19.i31
+
+bb15.i28:
+	br label %bb19.i31
+
+bb19.i31:
+	%y.0.i = phi i64 [ %t2, %bb15.i28 ], [ %t2, %bb14.i27 ]
+	br label %bb35.i
+
+bb35.i:
+	br i1 undef, label %bb37.i, label %bb14.i27
+
+bb37.i:
+	%t3 = add i64 %i.0.i35, 1
+	br label %bb38.i
+
+bb38.i:
+	%i.0.i35 = phi i64 [ 1, %entry ], [ %t3, %bb37.i ]
+	br label %bb35.i
+}