XFAIL the remote small code model tests on x86. Small code model is not properly

[oota-llvm.git] / docs / FAQ.rst

diff --git a/docs/FAQ.rst b/docs/FAQ.rst
index 67e8d0b27b26ee4ba991b638b6bd24c6643eb639..0559a1ff21505988bcc43e225886edd17fc29c49 100644 (file)
--- a/docs/FAQ.rst
+++ b/docs/FAQ.rst
@@ -1,5 +1,3 @@
-.. _faq:
-
 ================================
 Frequently Asked Questions (FAQ)
 ================================
@@ -53,6 +51,29 @@ Some porting problems may exist in the following areas:
   like the Bourne Shell and sed.  Porting to systems without these tools
   (MacOS 9, Plan 9) will require more effort.
 
+What API do I use to store a value to one of the virtual registers in LLVM IR's SSA representation?
+---------------------------------------------------------------------------------------------------
+
+In short: you can't. It's actually kind of a silly question once you grok
+what's going on. Basically, in code like:
+
+.. code-block:: llvm
+
+    %result = add i32 %foo, %bar
+
+, ``%result`` is just a name given to the ``Value`` of the ``add``
+instruction. In other words, ``%result`` *is* the add instruction. The
+"assignment" doesn't explicitly "store" anything to any "virtual register";
+the "``=``" is more like the mathematical sense of equality.
+
+Longer explanation: In order to generate a textual representation of the
+IR, some kind of name has to be given to each instruction so that other
+instructions can textually reference it. However, the isomorphic in-memory
+representation that you manipulate from C++ has no such restriction since
+instructions can simply keep pointers to any other ``Value``'s that they
+reference. In fact, the names of dummy numbered temporaries like ``%1`` are
+not explicitly represented in the in-memory representation at all (see
+``Value::getName()``).
 
 Build Problems
 ==============
@@ -81,7 +102,7 @@ grabbing the wrong linker/assembler/etc, there are two ways to fix it:
 
 .. code-block:: console
 
-   % PATH=[the path without the bad program] ./configure ...
+   % PATH=[the path without the bad program] $LLVM_SRC_DIR/configure ...
 
 This is still somewhat inconvenient, but it allows ``configure`` to do its
 work without having to adjust your ``PATH`` permanently.
@@ -163,14 +184,6 @@ This is `a bug in GCC <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13392>`_,
 and affects projects other than LLVM.  Try upgrading or downgrading your GCC.
 
 
-Compiling LLVM with GCC succeeds, but the resulting tools do not work, what can be wrong?
------------------------------------------------------------------------------------------
-Several versions of GCC have shown a weakness in miscompiling the LLVM
-codebase.  Please consult your compiler version (``gcc --version``) to find
-out whether it is `broken <GettingStarted.html#brokengcc>`_.  If so, your only
-option is to upgrade GCC to a known good version.
-
-
 After Subversion update, rebuilding gives the error "No rule to make target".
 -----------------------------------------------------------------------------
 If the error is of the form: