From 8b77454dff820832259acefe45e4254203760f19 Mon Sep 17 00:00:00 2001
From: David Majnemer <david.majnemer@gmail.com>
Date: Mon, 16 Feb 2015 19:10:02 +0000
Subject: [PATCH] ConstantFold: Properly fold GEP indices wider than i64

llvm-svn: 229420
---
 llvm/lib/IR/ConstantFold.cpp         | 49 +++++++++++++++++++++++-------------
 llvm/test/Assembler/getelementptr.ll |  6 +++++
 2 files changed, 37 insertions(+), 18 deletions(-)

diff --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 9176bf2..16ecf1c 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -1282,15 +1282,17 @@ static int IdxCompare(Constant *C1, Constant *C2, Type *ElTy) {
   if (!isa<ConstantInt>(C1) || !isa<ConstantInt>(C2))
     return -2; // don't know!
 
-  // Ok, we have two differing integer indices.  Sign extend them to be the same
-  // type.  Long is always big enough, so we use it.
-  if (!C1->getType()->isIntegerTy(64))
-    C1 = ConstantExpr::getSExt(C1, Type::getInt64Ty(C1->getContext()));
+  // We cannot compare the indices if they don't fit in an int64_t.
+  if (cast<ConstantInt>(C1)->getValue().getActiveBits() > 64 ||
+      cast<ConstantInt>(C2)->getValue().getActiveBits() > 64)
+    return -2; // don't know!
 
-  if (!C2->getType()->isIntegerTy(64))
-    C2 = ConstantExpr::getSExt(C2, Type::getInt64Ty(C1->getContext()));
+  // Ok, we have two differing integer indices.  Sign extend them to be the same
+  // type.
+  int64_t C1Val = cast<ConstantInt>(C1)->getSExtValue();
+  int64_t C2Val = cast<ConstantInt>(C2)->getSExtValue();
 
-  if (C1 == C2) return 0;  // They are equal
+  if (C1Val == C2Val) return 0;  // They are equal
 
   // If the type being indexed over is really just a zero sized type, there is
   // no pointer difference being made here.
@@ -1299,8 +1301,7 @@ static int IdxCompare(Constant *C1, Constant *C2, Type *ElTy) {
 
   // If they are really different, now that they are the same type, then we
   // found a difference!
-  if (cast<ConstantInt>(C1)->getSExtValue() < 
-      cast<ConstantInt>(C2)->getSExtValue())
+  if (C1Val < C2Val)
     return -1;
   else
     return 1;
@@ -2088,9 +2089,15 @@ static Constant *ConstantFoldGetElementPtrImpl(Constant *C,
         if (!Idx0->isNullValue()) {
           Type *IdxTy = Combined->getType();
           if (IdxTy != Idx0->getType()) {
-            Type *Int64Ty = Type::getInt64Ty(IdxTy->getContext());
-            Constant *C1 = ConstantExpr::getSExtOrBitCast(Idx0, Int64Ty);
-            Constant *C2 = ConstantExpr::getSExtOrBitCast(Combined, Int64Ty);
+            unsigned CommonExtendedWidth =
+                std::max(IdxTy->getIntegerBitWidth(),
+                         Idx0->getType()->getIntegerBitWidth());
+            CommonExtendedWidth = std::max(CommonExtendedWidth, 64U);
+
+            Type *CommonTy =
+                Type::getIntNTy(IdxTy->getContext(), CommonExtendedWidth);
+            Constant *C1 = ConstantExpr::getSExtOrBitCast(Idx0, CommonTy);
+            Constant *C2 = ConstantExpr::getSExtOrBitCast(Combined, CommonTy);
             Combined = ConstantExpr::get(Instruction::Add, C1, C2);
           } else {
             Combined =
@@ -2163,14 +2170,20 @@ static Constant *ConstantFoldGetElementPtrImpl(Constant *C,
             Constant *PrevIdx = cast<Constant>(Idxs[i-1]);
             Constant *Div = ConstantExpr::getSDiv(CI, Factor);
 
+            unsigned CommonExtendedWidth =
+                std::max(PrevIdx->getType()->getIntegerBitWidth(),
+                         Div->getType()->getIntegerBitWidth());
+            CommonExtendedWidth = std::max(CommonExtendedWidth, 64U);
+
             // Before adding, extend both operands to i64 to avoid
             // overflow trouble.
-            if (!PrevIdx->getType()->isIntegerTy(64))
-              PrevIdx = ConstantExpr::getSExt(PrevIdx,
-                                           Type::getInt64Ty(Div->getContext()));
-            if (!Div->getType()->isIntegerTy(64))
-              Div = ConstantExpr::getSExt(Div,
-                                          Type::getInt64Ty(Div->getContext()));
+            if (!PrevIdx->getType()->isIntegerTy(CommonExtendedWidth))
+              PrevIdx = ConstantExpr::getSExt(
+                  PrevIdx,
+                  Type::getIntNTy(Div->getContext(), CommonExtendedWidth));
+            if (!Div->getType()->isIntegerTy(CommonExtendedWidth))
+              Div = ConstantExpr::getSExt(
+                  Div, Type::getIntNTy(Div->getContext(), CommonExtendedWidth));
 
             NewIdxs[i-1] = ConstantExpr::getAdd(PrevIdx, Div);
           } else {
diff --git a/llvm/test/Assembler/getelementptr.ll b/llvm/test/Assembler/getelementptr.ll
index e938ff4..bd583af 100644
--- a/llvm/test/Assembler/getelementptr.ll
+++ b/llvm/test/Assembler/getelementptr.ll
@@ -8,6 +8,12 @@
 @C = global i32* getelementptr ([2 x [3 x [5 x [7 x i32]]]]* @A, i64 3, i64 2, i64 0, i64 0, i64 7523)
 ; CHECK: @C = global i32* getelementptr ([2 x [3 x [5 x [7 x i32]]]]* @A, i64 39, i64 1, i64 1, i64 4, i64 5)
 
+; Verify that constant expression GEPs work with i84 indices.
+@D = external global [1 x i32]
+
+@E = global i32* getelementptr inbounds ([1 x i32]* @D, i84 0, i64 1)
+; CHECK: @E = global i32* getelementptr inbounds ([1 x i32]* @D, i84 1, i64 0)
+
 ; Verify that i16 indices work.
 @x = external global {i32, i32}
 @y = global i32* getelementptr ({ i32, i32 }* @x, i16 42, i32 0)
-- 
2.7.4