From 7dd8dbf48652dfddd08cb7a6de0f2b079be45ea8 Mon Sep 17 00:00:00 2001
From: Peter Collingbourne <peter@pcc.me.uk>
Date: Fri, 22 Apr 2016 21:18:02 +0000
Subject: Introduce llvm.load.relative intrinsic.

This intrinsic takes two arguments, ``%ptr`` and ``%offset``. It loads
a 32-bit value from the address ``%ptr + %offset``, adds ``%ptr`` to that
value and returns it. The constant folder specifically recognizes the form of
this intrinsic and the constant initializers it may load from; if a loaded
constant initializer is known to have the form ``i32 trunc(x - %ptr)``,
the intrinsic call is folded to ``x``.

LLVM provides that the calculation of such a constant initializer will
not overflow at link time under the medium code model if ``x`` is an
``unnamed_addr`` function. However, it does not provide this guarantee for
a constant initializer folded into a function body. This intrinsic can be
used to avoid the possibility of overflows when loading from such a constant.

Differential Revision: http://reviews.llvm.org/D18367

llvm-svn: 267223
---
 llvm/lib/CodeGen/CodeGen.cpp | 1 +
 1 file changed, 1 insertion(+)

(limited to 'llvm/lib/CodeGen/CodeGen.cpp')

diff --git a/llvm/lib/CodeGen/CodeGen.cpp b/llvm/lib/CodeGen/CodeGen.cpp
index ca3b36c17f1b..7ab69d7c326d 100644
--- a/llvm/lib/CodeGen/CodeGen.cpp
+++ b/llvm/lib/CodeGen/CodeGen.cpp
@@ -63,6 +63,7 @@ void llvm::initializeCodeGen(PassRegistry &Registry) {
   initializePostMachineSchedulerPass(Registry);
   initializePostRAHazardRecognizerPass(Registry);
   initializePostRASchedulerPass(Registry);
+  initializePreISelIntrinsicLoweringPass(Registry);
   initializeProcessImplicitDefsPass(Registry);
   initializeRegisterCoalescerPass(Registry);
   initializeShrinkWrapPass(Registry);
-- 
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