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| 5 <title>LLVM Assembly Language Reference Manual</title> | 5 <title>LLVM Assembly Language Reference Manual</title> |
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| 7 <meta name="author" content="Chris Lattner"> | 7 <meta name="author" content="Chris Lattner"> |
| 8 <meta name="description" | 8 <meta name="description" |
| 9 content="LLVM Assembly Language Reference Manual."> | 9 content="LLVM Assembly Language Reference Manual."> |
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| 2316 <p>Any non-void instruction or constant expression other than a non-intrinsic | 2316 <p>Any non-void instruction or constant expression other than a non-intrinsic |
| 2317 call, invoke, or phi with a trap operand has trap as its result value. Any | 2317 call, invoke, or phi with a trap operand has trap as its result value. Any |
| 2318 instruction with a trap operand which may have side effects emits those side | 2318 instruction with a trap operand which may have side effects emits those side |
| 2319 effects as if it had an undef operand instead. Notwithstanding that, a store | 2319 effects as if it had an undef operand instead. Notwithstanding that, a store |
| 2320 of a trap value causes subsequent loads of the same memory to return a trap | 2320 of a trap value causes subsequent loads of the same memory to return a trap |
| 2321 value. For example:</p> | 2321 value. For example:</p> |
| 2322 | 2322 |
| 2323 <div class="doc_code"> | 2323 <div class="doc_code"> |
| 2324 <pre> | 2324 <pre> |
| 2325 %trap = sub nuw i32 0, 1 ; Results in a trap value. | 2325 %trap = sub nuw i32 0, 1 ; Results in a trap value. |
| 2326 volatile store i32 %trap, i32* @g ; External observations of @g see undef. | |
| 2327 %trap2 = load i32* @g ; Returns a trap value, not just undef. | |
| 2328 %still_trap = and i32 %trap, 0 ; Whereas (and i32 undef, 0) would return 0. | 2326 %still_trap = and i32 %trap, 0 ; Whereas (and i32 undef, 0) would return 0. |
| 2329 %trap_yet_again = getelementptr i32* @h, i32 %still_trap | 2327 %trap_yet_again = getelementptr i32* @h, i32 %still_trap |
| 2330 store i32 0, i32* %trap_yet_again ; undefined behavior | 2328 store i32 0, i32* %trap_yet_again ; undefined behavior |
| 2329 |
| 2330 volatile store i32 %trap, i32* @g ; External observations of @g see undef. |
| 2331 %trap2 = load i32* @g ; Returns a trap value, not just undef. |
| 2331 </pre> | 2332 </pre> |
| 2332 </div> | 2333 </div> |
| 2333 | 2334 |
| 2334 <p>A <a href="#i_br">br</a> or <a href="#i_switch">switch</a> instruction whose | 2335 <p>A <a href="#i_br">br</a> or <a href="#i_switch">switch</a> instruction whose |
| 2335 control operand is a trap value causes undefined behavior.</p> | 2336 control operand is a trap value results in undefined behavior.</p> |
| 2336 | 2337 |
| 2337 <p>There is currently no way of representing a trap constant in the IR; they | 2338 <p>There is currently no way of representing a trap constant in the IR; they |
| 2338 only exist when produced by certain instructions, such as an | 2339 only exist when produced by certain instructions, such as an |
| 2339 <a href="#i_add"><tt>add</tt></a> with the <tt>nsw</tt> flag | 2340 <a href="#i_add"><tt>add</tt></a> with the <tt>nsw</tt> flag |
| 2340 set, when overflow occurs.</p> | 2341 set, when overflow occurs.</p> |
| 2341 | 2342 |
| 2342 </div> | 2343 </div> |
| 2343 | 2344 |
| 2344 <!-- ======================================================================= --> | 2345 <!-- ======================================================================= --> |
| 2345 <div class="doc_subsection"><a name="blockaddress">Addresses of Basic | 2346 <div class="doc_subsection"><a name="blockaddress">Addresses of Basic |
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| 7668 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br> | 7669 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br> |
| 7669 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br> | 7670 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br> |
| 7670 Last modified: $Date$ | 7671 Last modified: $Date$ |
| 7671 </address> | 7672 </address> |
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| 7673 </body> | 7674 </body> |
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