Am 17.04.2016 um 11:06 schrieb Jose Fonseca:
> On 16/04/16 22:30, srol...@vmware.com wrote:
>> From: Roland Scheidegger <srol...@vmware.com>
>>
>> llvm 3.7 sometimes simply miscompiles vector selects.
>
> Reviewed-by: Jose Fonseca <jfons...@vmware.com>
>
>> See https://bugs.freedesktop.org/show_bug.cgi?id=94972
>
> Great detective work.
>
> I think you should make a LLVM test case out of the IR on that bug and
> propose on llvm-commits, to guarantee it won't regress again. See
> test/CodeGen/X86/vselect-avx.ll for example.
After some more digging, there actually IS already a test for this
(pretty much exactly the same as mine). It was in 3.7 as well - of
course not very helpful with the wrong expected result...
This fixed it:
commit 30ead638b8b7ad4d70d25ef3c70f0d6b21522784
Author: Michael Kuperstein <michael.m.kuperst...@intel.com>
Date: Thu Oct 8 08:13:02 2015 +0000
[X86] Fix wrong treatment of multi-lane blends in
BUILD_VECTORtoBlendMask()
This fixes two separate bugs:
1) The mask for the high lane was not set correctly. That fixes PR24532.
2) The transformation should bail out if it believes it involves
more than
2 lanes, as it does not currently do anything sensible in this case.
Differential Revision: http://reviews.llvm.org/D13505
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249669
91177308-0d34-0410-b5e6-96231b3b80d8
Roland
>
> Jose
>
>> ---
>> src/gallium/auxiliary/gallivm/lp_bld_logic.c | 8 +++++---
>> 1 file changed, 5 insertions(+), 3 deletions(-)
>>
>> diff --git a/src/gallium/auxiliary/gallivm/lp_bld_logic.c
>> b/src/gallium/auxiliary/gallivm/lp_bld_logic.c
>> index 91f316c..620aece 100644
>> --- a/src/gallium/auxiliary/gallivm/lp_bld_logic.c
>> +++ b/src/gallium/auxiliary/gallivm/lp_bld_logic.c
>> @@ -315,14 +315,16 @@ lp_build_select(struct lp_build_context *bld,
>> mask = LLVMBuildTrunc(builder, mask,
>> LLVMInt1TypeInContext(lc), "");
>> res = LLVMBuildSelect(builder, mask, a, b, "");
>> }
>> - else if (LLVMIsConstant(mask) ||
>> - LLVMGetInstructionOpcode(mask) == LLVMSExt) {
>> + else if (!(HAVE_LLVM == 0x0307) &&
>> + (LLVMIsConstant(mask) ||
>> + LLVMGetInstructionOpcode(mask) == LLVMSExt)) {
>> /* Generate a vector select.
>> *
>> * Using vector selects should avoid emitting intrinsics hence
>> avoid
>> - * hidering optimization passes, but vector selects weren't
>> properly
>> + * hindering optimization passes, but vector selects weren't
>> properly
>> * supported yet for a long time, and LLVM will generate poor
>> code when
>> * the mask is not the result of a comparison.
>> + * Also, llvm 3.7 may miscompile them (bug 94972).
>> */
>>
>> /* Convert the mask to a vector of booleans.
>>
>
>
>
>
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