[PATCH] Fix PR17168 (DAG scheduler inserts DBG_VALUE before PHI with fast-isel)

[Bill Schmidt]

Ping.

Thanks,
Bill

On Wed, 2013-10-02 at 15:10 -0500, Bill Schmidt wrote:
> PR17168 describes a test case that fails when compiling for debug with
> fast-isel.  Investigation showed that the test was failing because a
> DBG_VALUE machine instruction was placed prior to a PHI.
> 
> For this problem to occur requires the following:
>  * Compile for debug
>  * Compile with fast-isel
>  * In a block B, fast-isel must partially succeed before punting to DAG-isel
>  * B must start with a PHI
>  * The first unhandled node in the DAG must not generate a machine instruction
>  * A debug value with an order less than that of that first node exists
> 
> When all of these circumstances apply, the existing test that an
> instruction was not inserted won't fire.  Currently it tests whether the
> block is empty, or whether the last instruction generated is a phi.
> When fast-isel has partially succeeded, the last instruction generated
> will not be a phi.  Instead, we need to check whether the current insert
> position is immediately following a phi.  This patch adds that check,
> and adds the test case from the PR as a regression test.
> 
> Tested on powerpc64-unknown-linux-gnu with no regressions.  Is this ok
> to commit?
> 
> Thanks,
> Bill
> 
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