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asm goto vs simulate_block

From: Richard Henderson <rth at twiddle dot net>
To: dberlin at dberlin dot org
Cc: "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>, law at redhat dot com
Date: Thu, 27 Aug 2009 10:23:50 -0700
Subject: asm goto vs simulate_block

The kernel folk here at Red Hat have given me a test case (which I'll be happy to forward, along a complete patch vs mainline) which gets miscompiled because we never get around to adding all of the appropriate blocks outgoing from an asm-goto to the simulation.

I can't figure out why the VARYING that we get in simulate_stmt and subsequent calls to add_control_edge are not enough to DTRT. All I know is that the attached patch does in fact work around the problem, changing the .028t.ccp1 dump:

...
 Lattice value changed to VARYING.  Adding SSA edges to worklist.
+Adding Destination of edge (13 -> 14) to worklist
+
+
+Simulating block 14
...

Can someone give me a good explanation as to why this patch would be needed?

r~

Attachment: d-asmgoto-5
Description: Text document

Follow-Ups:
- Re: asm goto vs simulate_block
  - From: Daniel Berlin

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