[PATCH] Verify 'optnone' can run DAG combiner when appropriate

[Robinson, Paul]

"What caused you to notice not running the DAG combiner was a problem?"

A fuzzer that we wrote generated some functions with 'optnone' and they crashed the compiler with instruction-selection failures.
Being mostly vector-related, Andrea looked at them, and didn't take long to point the finger at DAG combine (or lack thereof!).

Should I take this to imply you'd rather have one of the causes-a-crash functions as the test, instead of this one?
--paulr

From: Eric Christopher [mailto:echristo at gmail.com]
Sent: Wednesday, March 25, 2015 4:44 PM
To: reviews+D8614+public+1ca59dfb9fe35dfd at reviews.llvm.org; Robinson, Paul; dblaikie at gmail.com
Cc: llvm-commits at cs.uiuc.edu
Subject: Re: [PATCH] Verify 'optnone' can run DAG combiner when appropriate


On Wed, Mar 25, 2015 at 1:28 PM Eric Christopher <echristo at gmail.com<mailto:echristo at gmail.com>> wrote:
Inline comment.


================
Comment at: test/CodeGen/X86/dag-optnone.ll:7
@@ +6,3 @@
+; that the combine is expected.
+; Note, this will start failing if somebody decides that this combine should
+; not occur at -O0 (because 'optnone' essentially sets -O0 for the function).
----------------
Could you describe the problem that would occur were the dag combiner not run? That hasn't been clear either in this test or in your original commit reverting.

Resending because I typoed and it's unclear I think:

"What caused you to notice not running the DAG combiner was a problem?"

-eric

http://reviews.llvm.org/D8614

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