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Add a WHOLE lot of updates clarifications and fixes. This is not done but getting closer. I changed the docs to reflect the goal of making unwind an instruction, not an intrinsic.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@8337 91177308-0d34-0410-b5e6-96231b3b80d8
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Chris Lattner 2003-09-03 00:41:47 +00:00
parent fde246a42f
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1 changed files with 133 additions and 77 deletions
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@ -39,6 +39,7 @@
<li><a href="#i_br" >'<tt>br</tt>' Instruction</a>
<li><a href="#i_switch">'<tt>switch</tt>' Instruction</a>
<li><a href="#i_invoke">'<tt>invoke</tt>' Instruction</a>
<li><a href="#i_unwind" >'<tt>unwind</tt>' Instruction</a>
</ol>
<li><a href="#binaryops">Binary Operations</a>
<ol>
@ -81,7 +82,6 @@
<li><a href="#i_va_start">'<tt>llvm.va_start</tt>' Intrinsic</a>
<li><a href="#i_va_end" >'<tt>llvm.va_end</tt>' Intrinsic</a>
<li><a href="#i_va_copy" >'<tt>llvm.va_copy</tt>' Intrinsic</a>
<li><a href="#i_unwind" >'<tt>llvm.unwind</tt>' Intrinsic</a>
</ol>
</ol>
@ -167,9 +167,17 @@ passes or input to the parser.<p>
LLVM uses three different forms of identifiers, for different purposes:<p>
<ol>
<li>Numeric constants are represented as you would expect: 12, -3 123.421, etc. Floating point constants have an optional hexidecimal notation.
<li>Named values are represented as a string of characters with a '%' prefix. For example, %foo, %DivisionByZero, %a.really.long.identifier. The actual regular expression used is '<tt>%[a-zA-Z$._][a-zA-Z$._0-9]*</tt>'.
<li>Unnamed values are represented as an unsigned numeric value with a '%' prefix. For example, %12, %2, %44.
<li>Numeric constants are represented as you would expect: 12, -3 123.421, etc.
Floating point constants have an optional hexidecimal notation.
<li>Named values are represented as a string of characters with a '%' prefix.
For example, %foo, %DivisionByZero, %a.really.long.identifier. The actual
regular expression used is '<tt>%[a-zA-Z$._][a-zA-Z$._0-9]*</tt>'. Identifiers
which require other characters in their names can be surrounded with quotes. In
this way, anything except a <tt>"</tt> character can be used in a name.
<li>Unnamed values are represented as an unsigned numeric value with a '%'
prefix. For example, %12, %2, %44.
</ol><p>
LLVM requires the values start with a '%' sign for two reasons: Compilers don't
@ -346,7 +354,7 @@ Here are some examples of multidimensional arrays:<p>
<ul>
<table border=0 cellpadding=0 cellspacing=0>
<tr><td><tt>[3 x [4 x int]]</tt></td><td>: 3x4 array integer values.</td></tr>
<tr><td><tt>[12 x [10 x float]]</tt></td><td>: 2x10 array of single precision floating point values.</td></tr>
<tr><td><tt>[12 x [10 x float]]</tt></td><td>: 12x10 array of single precision floating point values.</td></tr>
<tr><td><tt>[2 x [3 x [4 x uint]]]</tt></td><td>: 2x3x4 array of unsigned integer values.</td></tr>
</table>
</ul>
@ -369,10 +377,10 @@ functions), for indirect function calls, and when defining a function.<p>
Where '<tt>&lt;parameter list&gt;</tt>' is a comma-separated list of type
specifiers. Optionally, the parameter list may include a type <tt>...</tt>,
which indicates that the function takes a variable number of arguments. Note
that there currently is no way to define a function in LLVM that takes a
variable number of arguments, but it is possible to <b>call</b> a function that
is vararg.<p>
which indicates that the function takes a variable number of arguments.
Variable argument functions can access their arguments with the <a
href="#int_varargs">variable argument handling intrinsic</a> functions.
<p>
<h5>Examples:</h5>
<ul>
@ -490,13 +498,13 @@ declarations, and merges symbol table entries. Here is an example of the "hello
<pre>
<i>; Declare the string constant as a global constant...</i>
<a href="#identifiers">%.LC0</a> = <a href="#linkage_decl">internal</a> <a href="#globalvars">constant</a> <a href="#t_array">[13 x sbyte]</a> c"hello world\0A\00" <i>; [13 x sbyte]*</i>
<a href="#identifiers">%.LC0</a> = <a href="#linkage_internal">internal</a> <a href="#globalvars">constant</a> <a href="#t_array">[13 x sbyte]</a> c"hello world\0A\00" <i>; [13 x sbyte]*</i>
<i>; Forward declaration of puts</i>
<a href="#functionstructure">declare</a> int "puts"(sbyte*) <i>; int(sbyte*)* </i>
<i>; External declaration of the puts function</i>
<a href="#functionstructure">declare</a> int %puts(sbyte*) <i>; int(sbyte*)* </i>
<i>; Definition of main function</i>
int "main"() { <i>; int()* </i>
int %main() { <i>; int()* </i>
<i>; Convert [13x sbyte]* to sbyte *...</i>
%cast210 = <a href="#i_getelementptr">getelementptr</a> [13 x sbyte]* %.LC0, long 0, long 0 <i>; sbyte*</i>
@ -510,19 +518,56 @@ This example is made up of a <a href="#globalvars">global variable</a> named
"<tt>.LC0</tt>", an external declaration of the "<tt>puts</tt>" function, and a
<a href="#functionstructure">function definition</a> for "<tt>main</tt>".<p>
<a name="linkage_decl">
<a name="linkage">
In general, a module is made up of a list of global values, where both functions
and global variables are global values. Global values are represented by a
pointer to a memory location (in this case, a pointer to an array of char, and a
pointer to a function), and can be either "internal" or externally accessible
(which corresponds to the static keyword in C, when used at global scope).<p>
pointer to a function), and have one of the following linkage types:<p>
<dl>
<a name="linkage_internal">
<dt><tt><b>internal</b></tt>
<dd>Global values with internal linkage are only directly accessible by objects
in the current module. In particular, linking code into a module with an
internal global value may cause the internal to be renamed as necessary to avoid
collisions. Because the symbol is internal to the module, all references can be
updated. This corresponds to the notion of the '<tt>static</tt>' keyword in C,
or the idea of "anonymous namespaces" in C++.<p>
<a name="linkage_linkonce">
<dt><tt><b>linkonce</b></tt>:
<dd>"<tt>linkonce</tt>" linkage is similar to <tt>internal</tt> linkage, with
the twist that linking together two modules defining the same <tt>linkonce</tt>
globals will cause one of the globals to be discarded. This is typically used
to implement inline functions.<p>
<a name="linkage_appending">
<dt><tt><b>appending</b></tt>:
<dd>"<tt>appending</tt>" linkage may only applied to global variables of pointer
to array type. When two global variables with appending linkage are linked
together, the two global arrays are appended together. This is the LLVM,
typesafe, equivalent of having the system linker append together "sections" with
identical names when .o files are linked.<p>
<a name="linkage_external">
<dt><tt><b>externally visible</b></tt>:
<dd>If none of the above identifiers are used, the global is externally visible,
meaning that it participates in linkage and can be used to resolve external
symbol references.<p>
</dl><p>
For example, since the "<tt>.LC0</tt>" variable is defined to be internal, if
another module defined a "<tt>.LC0</tt>" variable and was linked with this one,
one of the two would be renamed, preventing a collision. Since "<tt>main</tt>"
and "<tt>puts</tt>" are external (i.e., lacking "<tt>internal</tt>"
declarations), they are accessible outside of the current module. It is illegal
for a function declaration to be "<tt>internal</tt>".<p>
and "<tt>puts</tt>" are external (i.e., lacking any linkage declarations), they
are accessible outside of the current module. It is illegal for a function
<i>declaration</i> to have any linkage type other than "externally visible".<p>
<!-- ======================================================================= -->
@ -547,7 +592,7 @@ of memory, and all memory objects in LLVM are accessed through pointers.<p>
<!-- ======================================================================= -->
</ul><table width="100%" bgcolor="#441188" border=0 cellpadding=4 cellspacing=0>
<tr><td>&nbsp;</td><td width="100%">&nbsp; <font color="#EEEEFF" face="Georgia,Palatino"><b>
<a name="functionstructure">Function Structure
<a name="functionstructure">Functions
</b></font></td></tr></table><ul>
LLVM functions definitions are composed of a (possibly empty) argument list, an
@ -564,7 +609,8 @@ return).<p>
The first basic block in program is special in two ways: it is immediately
executed on entrance to the function, and it is not allowed to have predecessor
basic blocks (i.e. there can not be any branches to the entry block of a
function).<p>
function). Because the block can have no predecessors, it also cannot have any
<a href="#i_phi">PHI nodes</a>.<p>
<!-- *********************************************************************** -->
@ -593,11 +639,12 @@ typically yield a '<tt>void</tt>' value: they produce control flow, not values
(the one exception being the '<a href="#i_invoke"><tt>invoke</tt></a>'
instruction).<p>
There are four different terminator instructions: the '<a
There are five different terminator instructions: the '<a
href="#i_ret"><tt>ret</tt></a>' instruction, the '<a
href="#i_br"><tt>br</tt></a>' instruction, the '<a
href="#i_switch"><tt>switch</tt></a>' instruction, and the '<a
href="#i_invoke"><tt>invoke</tt></a>' instruction.<p>
href="#i_switch"><tt>switch</tt></a>' instruction, the '<a
href="#i_invoke"><tt>invoke</tt></a>' instruction, and the '<a
href="#i_unwind"><tt>unwind</tt></a>' instruction.<p>
<!-- _______________________________________________________________________ -->
@ -628,8 +675,13 @@ that returns a value that does not match the return type of the function.<p>
<h5>Semantics:</h5>
When the '<tt>ret</tt>' instruction is executed, control flow returns back to
the calling function's context. If the instruction returns a value, that value
shall be propagated into the calling function's data space.<p>
the calling function's context. If the caller is a "<a
href="#i_call"><tt>call</tt></a> instruction, execution continues at the
instruction after the call. If the caller was an "<a
href="#i_invoke"><tt>invoke</tt></a>" instruction, execution continues at the
beginning "normal" of the destination block. If the instruction returns a
value, that value shall set the call or invoke instruction's return value.<p>
<h5>Example:</h5>
<pre>
@ -665,8 +717,8 @@ target.<p>
Upon execution of a conditional '<tt>br</tt>' instruction, the '<tt>bool</tt>'
argument is evaluated. If the value is <tt>true</tt>, control flows to the
'<tt>iftrue</tt>' '<tt>label</tt>' argument. If "cond" is <tt>false</tt>,
control flows to the '<tt>iffalse</tt>' '<tt>label</tt>' argument.<p>
'<tt>iftrue</tt>' <tt>label</tt> argument. If "cond" is <tt>false</tt>,
control flows to the '<tt>iffalse</tt>' <tt>label</tt> argument.<p>
<h5>Example:</h5>
<pre>
@ -685,7 +737,7 @@ IfUnequal:
<h5>Syntax:</h5>
<pre>
switch int &lt;value&gt;, label &lt;defaultdest&gt; [ int &lt;val&gt;, label &dest&gt;, ... ]
switch uint &lt;value&gt;, label &lt;defaultdest&gt; [ int &lt;val&gt;, label &dest&gt;, ... ]
</pre>
@ -718,15 +770,15 @@ conditional branches, or with a lookup table.<p>
<pre>
<i>; Emulate a conditional br instruction</i>
%Val = <a href="#i_cast">cast</a> bool %value to uint
switch int %Val, label %truedest [int 0, label %falsedest ]
switch uint %Val, label %truedest [int 0, label %falsedest ]
<i>; Emulate an unconditional br instruction</i>
switch int 0, label %dest [ ]
switch uint 0, label %dest [ ]
<i>; Implement a jump table:</i>
switch int %val, label %otherwise [ int 0, label %onzero,
int 1, label %onone,
int 2, label %ontwo ]
switch uint %val, label %otherwise [ int 0, label %onzero,
int 1, label %onone,
int 2, label %ontwo ]
</pre>
@ -744,11 +796,12 @@ conditional branches, or with a lookup table.<p>
The '<tt>invoke</tt>' instruction causes control to transfer to a specified
function, with the possibility of control flow transfer to either the
'<tt>normal label</tt>' label or the '<tt>exception label</tt>'. If the callee
function invokes the "<tt><a href="#i_ret">ret</a></tt>" instruction, control
flow will return to the "normal" label. If the callee (or any indirect callees)
calls the "<a href="#i_unwind"><tt>llvm.unwind</tt></a>" intrinsic, control is
interrupted, and continued at the "except" label.<p>
'<tt>normal</tt>' <tt>label</tt> label or the '<tt>exception</tt>'
<tt>label</tt>. If the callee function returns with the "<tt><a
href="#i_ret">ret</a></tt>" instruction, control flow will return to the
"normal" label. If the callee (or any indirect callees) returns with the "<a
href="#i_unwind"><tt>unwind</tt></a>" instruction, control is interrupted, and
continued at the dynamically nearest "except" label.<p>
<h5>Arguments:</h5>
@ -771,8 +824,8 @@ accepts a variable number of arguments, the extra arguments can be specified.
<li>'<tt>normal label</tt>': the label reached when the called function executes
a '<tt><a href="#i_ret">ret</a></tt>' instruction.
<li>'<tt>exception label</tt>': the label reached when a callee calls the <a
href="#i_unwind"><tt>llvm.unwind</tt></a> intrinsic.
<li>'<tt>exception label</tt>': the label reached when a callee returns with the
<a href="#i_unwind"><tt>unwind</tt></a> instruction.
</ol>
<h5>Semantics:</h5>
@ -793,6 +846,30 @@ exception. Additionally, this is important for implementation of
except label %TestCleanup <i>; {int}:retval set</i>
</pre>
<!-- _______________________________________________________________________ -->
</ul><a name="i_unwind"><h4><hr size=0>'<tt>unwind</tt>' Instruction</h4><ul>
<h5>Syntax:</h5>
<pre>
unwind
</pre>
<h5>Overview:</h5>
The '<tt>unwind</tt>' instruction unwinds the stack, continuing control flow at
the first callee in the dynamic call stack which used an <a
href="#i_invoke"><tt>invoke</tt></a> instruction to perform the call. This is
primarily used to implement exception handling.
<h5>Semantics:</h5>
The '<tt>unwind</tt>' intrinsic causes execution of the current function to
immediately halt. The dynamic call stack is then searched for the first <a
href="#i_invoke"><tt>invoke</tt></a> instruction on the call stack. Once found,
execution continues at the "exceptional" destination block specified by the
<tt>invoke</tt> instruction. If there is no <tt>invoke</tt> instruction in the
dynamic call chain, undefined behavior results.
<!-- ======================================================================= -->
@ -802,7 +879,7 @@ exception. Additionally, this is important for implementation of
Binary operators are used to do most of the computation in a program. They
require two operands, execute an operation on them, and produce a single value.
The result value of a binary operator is not neccesarily the same type as its
The result value of a binary operator is not necessarily the same type as its
operands.<p>
There are several different binary operators:<p>
@ -972,9 +1049,6 @@ href="#t_pointer">pointer</a> type (it is not possible to compare
'<tt>label</tt>'s, '<tt>array</tt>'s, '<tt>structure</tt>' or '<tt>void</tt>'
values, etc...). Both arguments must have identical types.<p>
The '<tt>setlt</tt>', '<tt>setgt</tt>', '<tt>setle</tt>', and '<tt>setge</tt>'
instructions do not operate on '<tt>bool</tt>' typed arguments.<p>
<h5>Semantics:</h5>
The '<tt>seteq</tt>' instruction yields a <tt>true</tt> '<tt>bool</tt>' value if
@ -1109,7 +1183,8 @@ The truth table used for the '<tt>or</tt>' instruction is:<p>
<h5>Overview:</h5>
The '<tt>xor</tt>' instruction returns the bitwise logical exclusive or of its
two operands.<p>
two operands. The <tt>xor</tt> is used to implement the "one's complement"
operation, which is the "~" operator in C.<p>
<h5>Arguments:</h5>
@ -1136,6 +1211,7 @@ The truth table used for the '<tt>xor</tt>' instruction is:<p>
&lt;result&gt; = xor int 4, %var <i>; yields {int}:result = 4 ^ %var</i>
&lt;result&gt; = xor int 15, 40 <i>; yields {int}:result = 39</i>
&lt;result&gt; = xor int 4, 8 <i>; yields {int}:result = 12</i>
&lt;result&gt; = xor int %V, -1 <i>; yields {int}:result = ~%V</i>
</pre>
@ -1211,7 +1287,9 @@ argument is unsigned, zero bits shall fill the empty positions.<p>
<a name="memoryops">Memory Access Operations
</b></font></td></tr></table><ul>
Accessing memory in SSA form is, well, sticky at best. This section describes how to read, write, allocate and free memory in LLVM.<p>
A key design point of an SSA-based representation is how it represents memory.
In LLVM, no memory locations are in SSA form, which makes things very simple.
This section describes how to read, write, allocate and free memory in LLVM.<p>
<!-- _______________________________________________________________________ -->
@ -1234,10 +1312,12 @@ system, and returns a pointer of the appropriate type to the program. The
second form of the instruction is a shorter version of the first instruction
that defaults to allocating one element.<p>
'<tt>type</tt>' must be a sized type<p>
'<tt>type</tt>' must be a sized type.<p>
<h5>Semantics:</h5>
Memory is allocated, a pointer is returned.<p>
Memory is allocated using the system "<tt>malloc</tt>" function, and a pointer
is returned.<p>
<h5>Example:</h5>
<pre>
@ -1308,7 +1388,9 @@ one element.<p>
Memory is allocated, a pointer is returned. '<tt>alloca</tt>'d memory is
automatically released when the function returns. The '<tt>alloca</tt>'
instruction is commonly used to represent automatic variables that must have an
address available, as well as spilled variables.<p>
address available. When the function returns (either with the <tt><a
href="#i_ret">ret</a></tt> or <tt><a href="#i_invoke">invoke</a></tt>
instructions), the memory is reclaimed.<p>
<h5>Example:</h5>
<pre>
@ -1803,32 +1885,6 @@ because the <tt><a href="i_va_begin">llvm.va_begin</a></tt> intrinsic may be
arbitrarily complex and require memory allocation, for example.<p>
<!-- _______________________________________________________________________ -->
</ul><a name="i_unwind"><h4><hr size=0>'<tt>llvm.unwind</tt>' Intrinsic</h4><ul>
<h5>Syntax:</h5>
<pre>
call void (void)* %llvm.unwind()
</pre>
<h5>Overview:</h5>
The '<tt>llvm.unwind</tt>' intrinsic unwinds the stack, continuing control flow
at the first callee in the dynamic call stack which used an <a
href="#i_invoke"><tt>invoke</tt></a> instruction to perform the call. This is
primarily used to implement exception handling.
<h5>Semantics:</h5>
The '<tt>llvm.unwind</tt>' intrinsic causes execution of the current function to
immediately halt. The dynamic call stack is then searched for the first <a
href="#i_invoke"><tt>invoke</tt></a> instruction on the call stack. Once found,
execution continues at the "exceptional" destination block specified by the
invoke instruction. If there is no <tt>invoke</tt> instruction in the dynamic
call chain, undefined behavior results.
<!-- *********************************************************************** -->
</ul>
<!-- *********************************************************************** -->
@ -1839,7 +1895,7 @@ call chain, undefined behavior results.
<address><a href="mailto:sabre@nondot.org">Chris Lattner</a></address>
<!-- Created: Tue Jan 23 15:19:28 CST 2001 -->
<!-- hhmts start -->
Last modified: Tue Sep 2 18:38:09 CDT 2003
Last modified: Tue Sep 2 19:41:01 CDT 2003
<!-- hhmts end -->
</font>
</body></html>