[PATCH] Bugfix for Codegen of atomic load/store ops.

[John McCall]

Thanks for taking this on.  Please test all the basic atomic operations, not just loads and stores, and ensure that the extra bits take on some sensible behavior.

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Comment at: test/CodeGen/x86_64-atomic-long_double.c:7
@@ +6,3 @@
+  // CHECK: load atomic i128*
+  // CHECK: bitcast x86_fp80* %{{.+}} to i128*
+  // CHECK: store i128 %{{.+}}, i128*
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You need to be more specific in this test.  You should be able to match the alloca.

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Comment at: test/CodeGen/x86_64-atomic-long_double.c:14
@@ +13,3 @@
+
+void  test_store(_Atomic long double *addr, long double val) {
+  // CHECK-LABEL: @test_store
----------------
This isn't good enough; x86_fp80's store size doesn't fill its rounded-up size.  So you also need to ensure that the extra bits have some consistent value — i.e. zero.  In other words, there needs to be a memset of the alloca to zero before you can store the long double into it.

http://reviews.llvm.org/D6499