From 24662395df3baa3c9edfa026810d3dd2d788b928 Mon Sep 17 00:00:00 2001
From: Wei Mi <wmi@google.com>
Date: Wed, 14 Sep 2016 04:39:50 +0000
Subject: [PATCH] Create a getelementptr instead of sub expr for
 ValueOffsetPair if the value is a pointer.

This patch is to fix PR30213. When expanding an expr based on ValueOffsetPair,
if the value is of pointer type, we can only create a getelementptr instead
of sub expr.

Differential Revision: https://reviews.llvm.org/D24088

llvm-svn: 281439
---
 llvm/lib/Analysis/ScalarEvolutionExpander.cpp      | 25 +++++++++++++--
 .../ScalarEvolution/scev-expander-reuse-gep.ll     | 36 ++++++++++++++++++++++
 2 files changed, 58 insertions(+), 3 deletions(-)
 create mode 100644 llvm/test/Analysis/ScalarEvolution/scev-expander-reuse-gep.ll

diff --git a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
index 8959645..6ad766b 100644
--- a/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Analysis/ScalarEvolutionExpander.cpp
@@ -1703,9 +1703,28 @@ Value *SCEVExpander::expand(const SCEV *S) {
 
   if (!V)
     V = visit(S);
-  else if (VO.second)
-    V = Builder.CreateSub(V, VO.second);
-
+  else if (VO.second) {
+    if (PointerType *Vty = dyn_cast<PointerType>(V->getType())) {
+      Type *Ety = Vty->getPointerElementType();
+      int64_t Offset = VO.second->getSExtValue();
+      int64_t ESize = SE.getTypeSizeInBits(Ety);
+      if ((Offset * 8) % ESize == 0) {
+        ConstantInt *Idx =
+            ConstantInt::getSigned(VO.second->getType(), -(Offset * 8) / ESize);
+        V = Builder.CreateGEP(Ety, V, Idx, "scevgep");
+      } else {
+        ConstantInt *Idx =
+            ConstantInt::getSigned(VO.second->getType(), -Offset);
+        unsigned AS = Vty->getAddressSpace();
+        V = Builder.CreateBitCast(V, Type::getInt8PtrTy(SE.getContext(), AS));
+        V = Builder.CreateGEP(Type::getInt8Ty(SE.getContext()), V, Idx,
+                              "uglygep");
+        V = Builder.CreateBitCast(V, Vty);
+      }
+    } else {
+      V = Builder.CreateSub(V, VO.second);
+    }
+  }
   // Remember the expanded value for this SCEV at this location.
   //
   // This is independent of PostIncLoops. The mapped value simply materializes
diff --git a/llvm/test/Analysis/ScalarEvolution/scev-expander-reuse-gep.ll b/llvm/test/Analysis/ScalarEvolution/scev-expander-reuse-gep.ll
new file mode 100644
index 0000000..fd47b08
--- /dev/null
+++ b/llvm/test/Analysis/ScalarEvolution/scev-expander-reuse-gep.ll
@@ -0,0 +1,36 @@
+; PR30213. Check scev expand will generate correct code if the value
+; in ValueOffsetPair is of pointer type.
+; RUN: opt -mtriple=i386-apple-macosx10.12.0 < %s -loop-reduce -S | FileCheck %s
+
+; CHECK: %ptr4.ptr1 = select i1 %cmp.i, i8* %ptr4, i8* %ptr1
+; CHECK-NEXT: %scevgep = getelementptr i8, i8* %ptr4.ptr1, i32 1
+; CHECK-NEXT: br label %while.cond.i
+
+target datalayout = "e-m:o-p:32:32-f64:32:64-f80:128-n8:16:32-S128"
+target triple = "i386-apple-macosx10.12.0"
+
+; Function Attrs: nounwind optsize ssp
+define void @Foo() {
+entry:
+  switch i2 undef, label %sw.epilog102 [
+    i2 -2, label %sw.bb28
+  ]
+
+sw.bb28:                                          ; preds = %entry
+  %0 = load i8*, i8** undef, align 2
+  %ptr1 = getelementptr inbounds i8, i8* undef, i32 -1
+  %ptr4 = getelementptr inbounds i8, i8* %0, i32 -1
+  %cmp.i = icmp ult i8* undef, %0
+  %ptr4.ptr1 = select i1 %cmp.i, i8* %ptr4, i8* %ptr1
+  br label %while.cond.i
+
+while.cond.i:                                     ; preds = %while.cond.i, %sw.bb28
+  %currPtr.1.i = phi i8* [ %incdec.ptr.i, %while.cond.i ], [ %ptr4.ptr1, %sw.bb28 ]
+  %incdec.ptr.i = getelementptr inbounds i8, i8* %currPtr.1.i, i32 1
+  %1 = load i8, i8* %incdec.ptr.i, align 1
+  br label %while.cond.i
+
+sw.epilog102:                                     ; preds = %entry
+  unreachable
+}
+
-- 
2.7.4