From 7246a69d2bc0c709228241daa62ea2fa75c2a034 Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Sun, 3 Jan 2010 18:09:40 +0000
Subject: [PATCH] differences between two blockaddress's don't cause a global
 variable initializer to require relocations.

llvm-svn: 92450
---
 lib/VMCore/Constants.cpp                  | 18 ++++++++++++++++++
 test/CodeGen/X86/addr-label-difference.ll | 21 +++++++++++++++++++++
 2 files changed, 39 insertions(+)
 create mode 100644 test/CodeGen/X86/addr-label-difference.ll

diff --git a/lib/VMCore/Constants.cpp b/lib/VMCore/Constants.cpp
index e3c6144c76a..64fb0aa53bf 100644
--- a/lib/VMCore/Constants.cpp
+++ b/lib/VMCore/Constants.cpp
@@ -197,6 +197,24 @@ Constant::PossibleRelocationsTy Constant::getRelocationInfo() const {
   if (const BlockAddress *BA = dyn_cast<BlockAddress>(this))
     return BA->getFunction()->getRelocationInfo();
   
+  // While raw uses of blockaddress need to be relocated, differences between
+  // two of them don't when they are for labels in the same function.  This is a
+  // common idiom when creating a table for the indirect goto extension, so we
+  // handle it efficiently here.
+  if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(this))
+    if (CE->getOpcode() == Instruction::Sub) {
+      ConstantExpr *LHS = dyn_cast<ConstantExpr>(CE->getOperand(0));
+      ConstantExpr *RHS = dyn_cast<ConstantExpr>(CE->getOperand(1));
+      if (LHS && RHS &&
+          LHS->getOpcode() == Instruction::PtrToInt &&
+          RHS->getOpcode() == Instruction::PtrToInt &&
+          isa<BlockAddress>(LHS->getOperand(0)) &&
+          isa<BlockAddress>(RHS->getOperand(0)) &&
+          cast<BlockAddress>(LHS->getOperand(0))->getFunction() ==
+            cast<BlockAddress>(RHS->getOperand(0))->getFunction())
+        return NoRelocation;
+    }
+  
   PossibleRelocationsTy Result = NoRelocation;
   for (unsigned i = 0, e = getNumOperands(); i != e; ++i)
     Result = std::max(Result,
diff --git a/test/CodeGen/X86/addr-label-difference.ll b/test/CodeGen/X86/addr-label-difference.ll
new file mode 100644
index 00000000000..0c707c9a5d7
--- /dev/null
+++ b/test/CodeGen/X86/addr-label-difference.ll
@@ -0,0 +1,21 @@
+; RUN: llc %s -o - | grep {__TEXT,__const}
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128-n8:16:32"
+target triple = "i386-apple-darwin10.0"
+
+; This array should go into the __TEXT,__const section, not into the
+; __DATA,__const section, because the elements don't need relocations.
+@test.array = internal constant [3 x i32] [i32 sub (i32 ptrtoint (i8* blockaddress(@test, %foo) to i32), i32 ptrtoint (i8* blockaddress(@test, %foo) to i32)), i32 sub (i32 ptrtoint (i8* blockaddress(@test, %bar) to i32), i32 ptrtoint (i8* blockaddress(@test, %foo) to i32)), i32 sub (i32 ptrtoint (i8* blockaddress(@test, %hack) to i32), i32 ptrtoint (i8* blockaddress(@test, %foo) to i32))] ; <[3 x i32]*> [#uses=1]
+
+define void @test(i32 %i) nounwind ssp {
+entry:
+  br label %foo
+
+foo:                                              ; preds = %indirectgoto, %indirectgoto, %indirectgoto, %indirectgoto, %indirectgoto
+  br label %bar
+
+bar:                                              ; preds = %foo, %indirectgoto
+  br label %hack
+
+hack:                                             ; preds = %bar, %indirectgoto
+  ret void
+}