From c70c37794fbff2c615d4f9dc3b6adf9583b855dc Mon Sep 17 00:00:00 2001
From: Dan Gohman <gohman@apple.com>
Date: Sat, 26 Sep 2009 16:11:57 +0000
Subject: [PATCH] Fix a case where ScalarEvolution was expanding pointer
 arithmetic to inttoptr/ptrtoint unnecessarily.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@82864 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ScalarEvolutionExpander.cpp      | 23 +++++++++--
 .../preserve-gep-loop-variant.ll              | 41 +++++++++++++++++++
 2 files changed, 61 insertions(+), 3 deletions(-)
 create mode 100644 test/Transforms/IndVarSimplify/preserve-gep-loop-variant.ll

diff --git a/lib/Analysis/ScalarEvolutionExpander.cpp b/lib/Analysis/ScalarEvolutionExpander.cpp
index 34724709b0f..fd37d7bc1e3 100644
--- a/lib/Analysis/ScalarEvolutionExpander.cpp
+++ b/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -508,20 +508,37 @@ Value *SCEVExpander::expandAddToGEP(const SCEV *const *op_begin,
 }
 
 Value *SCEVExpander::visitAddExpr(const SCEVAddExpr *S) {
+  int NumOperands = S->getNumOperands();
   const Type *Ty = SE.getEffectiveSCEVType(S->getType());
-  Value *V = expand(S->getOperand(S->getNumOperands()-1));
+
+  // Find the index of an operand to start with. Choose the operand with
+  // pointer type, if there is one, or the last operand otherwise.
+  int PIdx = 0;
+  for (; PIdx != NumOperands - 1; ++PIdx)
+    if (isa<PointerType>(S->getOperand(PIdx)->getType())) break;
+
+  // Expand code for the operand that we chose.
+  Value *V = expand(S->getOperand(PIdx));
 
   // Turn things like ptrtoint+arithmetic+inttoptr into GEP. See the
   // comments on expandAddToGEP for details.
   if (const PointerType *PTy = dyn_cast<PointerType>(V->getType())) {
+    // Take the operand at PIdx out of the list.
     const SmallVectorImpl<const SCEV *> &Ops = S->getOperands();
-    return expandAddToGEP(&Ops[0], &Ops[Ops.size() - 1], PTy, Ty, V);
+    SmallVector<const SCEV *, 8> NewOps;
+    NewOps.insert(NewOps.end(), Ops.begin(), Ops.begin() + PIdx);
+    NewOps.insert(NewOps.end(), Ops.begin() + PIdx + 1, Ops.end());
+    // Make a GEP.
+    return expandAddToGEP(NewOps.begin(), NewOps.end(), PTy, Ty, V);
   }
 
+  // Otherwise, we'll expand the rest of the SCEVAddExpr as plain integer
+  // arithmetic.
   V = InsertNoopCastOfTo(V, Ty);
 
   // Emit a bunch of add instructions
-  for (int i = S->getNumOperands()-2; i >= 0; --i) {
+  for (int i = NumOperands-1; i >= 0; --i) {
+    if (i == PIdx) continue;
     Value *W = expandCodeFor(S->getOperand(i), Ty);
     V = InsertBinop(Instruction::Add, V, W);
   }
diff --git a/test/Transforms/IndVarSimplify/preserve-gep-loop-variant.ll b/test/Transforms/IndVarSimplify/preserve-gep-loop-variant.ll
new file mode 100644
index 00000000000..86e90c7623d
--- /dev/null
+++ b/test/Transforms/IndVarSimplify/preserve-gep-loop-variant.ll
@@ -0,0 +1,41 @@
+; RUN: opt < %s -indvars -S > %t
+; RUN: not grep inttoptr %t
+; RUN: not grep ptrtoint %t
+; RUN: grep scevgep %t
+
+; Indvars shouldn't need inttoptr/ptrtoint to expand an address here.
+
+define void @foo(i8* %p) nounwind {
+entry:
+  br i1 true, label %bb.nph, label %for.end
+
+for.cond:
+  %phitmp = icmp slt i64 %inc, 20
+  br i1 %phitmp, label %for.body, label %for.cond.for.end_crit_edge
+
+for.cond.for.end_crit_edge:
+  br label %for.end
+
+bb.nph:
+  br label %for.body
+
+for.body:
+  %storemerge1 = phi i64 [ %inc, %for.cond ], [ 0, %bb.nph ]
+  %call = tail call i64 @bar() nounwind
+  %call2 = tail call i64 @car() nounwind
+  %conv = trunc i64 %call2 to i8
+  %conv3 = sext i8 %conv to i64
+  %add = add nsw i64 %call, %storemerge1
+  %add4 = add nsw i64 %add, %conv3
+  %arrayidx = getelementptr inbounds i8* %p, i64 %add4
+  store i8 0, i8* %arrayidx
+  %inc = add nsw i64 %storemerge1, 1
+  br label %for.cond
+
+for.end:
+  ret void
+}
+
+declare i64 @bar()
+
+declare i64 @car()