[llvm] r305578 - [GVN] Recommit the patch "Add phi-translate support in scalarpre".

[Wei Mi via llvm-commits]

The patch caused the same buildbot error last time. I thought it was
the same error which will be by the recommit but apparently it is not.
I will look into it.

On Fri, Jun 16, 2017 at 2:08 PM, Davide Italiano <davide at freebsd.org> wrote:
> On Fri, Jun 16, 2017 at 1:21 PM, Wei Mi via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
>> Author: wmi
>> Date: Fri Jun 16 15:21:01 2017
>> New Revision: 305578
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=305578&view=rev
>> Log:
>> [GVN] Recommit the patch "Add phi-translate support in scalarpre".
>>
>> The recommit fixes two bugs: The first one is to use CurrentBlock instead of
>> PREInstr's Parent as param of performScalarPREInsertion because the Parent
>> of a clone instruction may be uninitialized. The second one is stop PRE when
>> CurrentBlock to its predecessor is a backedge and an operand of CurInst is
>> defined inside of CurrentBlock. The same value defined inside of loop in last
>> iteration can not be regarded as available.
>>
>> Right now scalarpre doesn't have phi-translate support, so it will miss some
>> simple pre opportunities. Like the following testcase, current scalarpre cannot
>> recognize the last "a * b" is fully redundent because a and b used by the last
>> "a * b" expr are both defined by phis.
>>
>> long a[100], b[100], g1, g2, g3;
>> __attribute__((pure)) long goo();
>>
>> void foo(long a, long b, long c, long d) {
>>
>>   g1 = a * b;
>>   if (__builtin_expect(g2 > 3, 0)) {
>>     a = c;
>>     b = d;
>>     g2 = a * b;
>>   }
>>   g3 = a * b;      // fully redundant.
>>
>> }
>> The patch adds phi-translate support in scalarpre. This is only a temporary
>> solution before the newpre based on newgvn is available.
>>
>> Differential Revision: https://reviews.llvm.org/D32252
>>
>
> This has unfortunately caused a bunch of failures, I think.
> Some of them look very weird as they're in NewGVN (which you didn't touch).
>
> http://lab.llvm.org:8011/builders/clang-x86_64-linux-selfhost-modules-2/builds/8569
>
> --
> Davide