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...in light of recent activity related to llvm.memcpy flags. I want to

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prevent an llvm developer from mistakenly thinking that just because the
intrinsic has volatile flags that volatile operations can be converted
to or folded into them.

Platforms may rely on volatile loads and stores of natively supported
data width to be executed as single instruction. When compiling
C, this expectation likely holds for l-values of volatile primitive
types with native hardware support, but not necessarily for aggregate
types. The frontend upholds these expectations, which are not
specified in the IR.

llvm-svn: 173974
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Andrew Trick 2013-01-30 21:19:35 +00:00
parent 7969f87a01
commit 4699474140
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@ -1080,6 +1080,11 @@ volatile operations. The optimizers *may* change the order of volatile
operations relative to non-volatile operations. This is not Java's
"volatile" and has no cross-thread synchronization behavior.
IR-level volatile loads and stores cannot safely be optimized into
llvm.memcpy or llvm.memmove intrinsics even when those intrinsics are
flagged volatile. Likewise, the backend should never split or merge
target-legal volatile load/store instructions.
.. _memmodel:
Memory Model for Concurrent Operations