From 38eb9f46db418ff8a75ef95841097a2ab6ebbc41 Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Thu, 4 Jun 2015 07:01:56 +0000
Subject: [PATCH] [ConstantFold] Don't skip the first gep index when folding
 geps

We neglected to check if the first index made the GEP ineligible for
'inbounds'.

This fixes PR23753.

llvm-svn: 239015
---
 llvm/lib/IR/ConstantFold.cpp                       |  6 ++---
 llvm/test/Transforms/LoopStrengthReduce/pr23753.ll | 29 ++++++++++++++++++++++
 2 files changed, 32 insertions(+), 3 deletions(-)
 create mode 100644 llvm/test/Transforms/LoopStrengthReduce/pr23753.ll

diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 3f64c43..2efc6124 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -2165,9 +2165,9 @@ static Constant *ConstantFoldGetElementPtrImpl(Type *PointeeTy, Constant *C,
   // factored out into preceding dimensions.
   bool Unknown = false;
   SmallVector<Constant *, 8> NewIdxs;
-  Type *Ty = PointeeTy;
-  Type *Prev = C->getType();
-  for (unsigned i = 1, e = Idxs.size(); i != e;
+  Type *Ty = C->getType();
+  Type *Prev = nullptr;
+  for (unsigned i = 0, e = Idxs.size(); i != e;
        Prev = Ty, Ty = cast<CompositeType>(Ty)->getTypeAtIndex(Idxs[i]), ++i) {
     if (ConstantInt *CI = dyn_cast<ConstantInt>(Idxs[i])) {
       if (isa<ArrayType>(Ty) || isa<VectorType>(Ty))
diff --git a/llvm/test/Transforms/LoopStrengthReduce/pr23753.ll b/llvm/test/Transforms/LoopStrengthReduce/pr23753.ll
new file mode 100644
index 0000000..a6a34b1
--- /dev/null
+++ b/llvm/test/Transforms/LoopStrengthReduce/pr23753.ll
@@ -0,0 +1,29 @@
+; RUN: opt < %s -loop-reduce -S | FileCheck %s
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+@a = external global i32, align 4
+@d = external global i8, align 1
+
+; CHECK-LABEL: void @f
+define void @f() {
+entry:
+  br label %for.body
+
+for.body:
+  %indvars.iv = phi i64 [ 0, %entry ], [ %indvars.iv.next, %for.body ]
+  %arrayidx = getelementptr inbounds i32, i32* @a, i64 %indvars.iv
+  %cmp = icmp ne i32* %arrayidx, bitcast (i8* @d to i32*)
+  %indvars.iv.next = add i64 %indvars.iv, 1
+  br i1 %cmp, label %for.body, label %for.end
+
+; CHECK:       %[[phi:.*]] = phi i8* [ %[[gep:.*]], {{.*}} ], [ getelementptr (i8, i8* @d, i64 sub (i64 4, i64 ptrtoint (i32* @a to i64))), {{.*}} ]
+; CHECK-NEXT:  %[[gep]]    = getelementptr i8, i8* %[[phi]], i64 -4
+; CHECK-NEXT:  %[[cst:.*]] = bitcast i8* %[[gep]] to i32*
+; CHECK-NEXT:  %[[cmp:.*]] = icmp ne i32* %[[cst]], null
+; CHECK-NEXT:  br i1 %[[cmp]]
+
+for.end:
+  ret void
+}
-- 
2.7.4