From 9d9e29b4a83818b066c09c8f832cec7641aa2115 Mon Sep 17 00:00:00 2001
From: Chandler Carruth <chandlerc@gmail.com>
Date: Sun, 25 Mar 2012 20:43:07 +0000
Subject: [PATCH] Switch the pointer-difference simplification logic to only
 work with inbounds GEPs. This isn't really necessary for simplifying pointer
 differences, but I'm planning to re-use the same code to simplify pointer
 comparisons where it is necessary. Since real code almost exclusively uses
 inbounds GEPs, it doesn't seem worth it to support the extra complexity of
 turning it on and off. If anyone would like that back, feel free to shout.
 Note that instcombine will still catch any of these patterns.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@153418 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/InstructionSimplify.cpp     |  2 +-
 test/Transforms/InstSimplify/ptr_diff.ll | 35 +++++++++++++++++-------
 2 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/lib/Analysis/InstructionSimplify.cpp b/lib/Analysis/InstructionSimplify.cpp
index aaf9de28da4..bb70d1cfc3c 100644
--- a/lib/Analysis/InstructionSimplify.cpp
+++ b/lib/Analysis/InstructionSimplify.cpp
@@ -710,7 +710,7 @@ static Constant *stripAndComputeConstantOffsets(const TargetData &TD,
   Visited.insert(V);
   do {
     if (GEPOperator *GEP = dyn_cast<GEPOperator>(V)) {
-      if (!accumulateGEPOffset(TD, GEP, Offset))
+      if (!GEP->isInBounds() || !accumulateGEPOffset(TD, GEP, Offset))
         break;
       V = GEP->getPointerOperand();
     } else if (Operator::getOpcode(V) == Instruction::BitCast) {
diff --git a/test/Transforms/InstSimplify/ptr_diff.ll b/test/Transforms/InstSimplify/ptr_diff.ll
index 013964ccfec..1eb1fd4c097 100644
--- a/test/Transforms/InstSimplify/ptr_diff.ll
+++ b/test/Transforms/InstSimplify/ptr_diff.ll
@@ -6,8 +6,8 @@ define i64 @ptrdiff1(i8* %ptr) {
 ; CHECK: @ptrdiff1
 ; CHECK-NEXT: ret i64 42
 
-  %first = getelementptr i8* %ptr, i32 0
-  %last = getelementptr i8* %ptr, i32 42
+  %first = getelementptr inbounds i8* %ptr, i32 0
+  %last = getelementptr inbounds i8* %ptr, i32 42
   %first.int = ptrtoint i8* %first to i64
   %last.int = ptrtoint i8* %last to i64
   %diff = sub i64 %last.int, %first.int
@@ -18,16 +18,31 @@ define i64 @ptrdiff2(i8* %ptr) {
 ; CHECK: @ptrdiff2
 ; CHECK-NEXT: ret i64 42
 
-  %first1 = getelementptr i8* %ptr, i32 0
-  %first2 = getelementptr i8* %first1, i32 1
-  %first3 = getelementptr i8* %first2, i32 2
-  %first4 = getelementptr i8* %first3, i32 4
-  %last1 = getelementptr i8* %first2, i32 48
-  %last2 = getelementptr i8* %last1, i32 8
-  %last3 = getelementptr i8* %last2, i32 -4
-  %last4 = getelementptr i8* %last3, i32 -4
+  %first1 = getelementptr inbounds i8* %ptr, i32 0
+  %first2 = getelementptr inbounds i8* %first1, i32 1
+  %first3 = getelementptr inbounds i8* %first2, i32 2
+  %first4 = getelementptr inbounds i8* %first3, i32 4
+  %last1 = getelementptr inbounds i8* %first2, i32 48
+  %last2 = getelementptr inbounds i8* %last1, i32 8
+  %last3 = getelementptr inbounds i8* %last2, i32 -4
+  %last4 = getelementptr inbounds i8* %last3, i32 -4
   %first.int = ptrtoint i8* %first4 to i64
   %last.int = ptrtoint i8* %last4 to i64
   %diff = sub i64 %last.int, %first.int
   ret i64 %diff
 }
+
+define i64 @ptrdiff3(i8* %ptr) {
+; Don't bother with non-inbounds GEPs.
+; CHECK: @ptrdiff3
+; CHECK: getelementptr
+; CHECK: sub
+; CHECK: ret
+
+  %first = getelementptr i8* %ptr, i32 0
+  %last = getelementptr i8* %ptr, i32 42
+  %first.int = ptrtoint i8* %first to i64
+  %last.int = ptrtoint i8* %last to i64
+  %diff = sub i64 %last.int, %first.int
+  ret i64 %diff
+}
-- 
2.34.1