[llvm] r228303 - R600/SI: Fix bug in TTI loop unrolling preferences

[Hans Wennborg]

Yes, go ahead.

Thanks,
Hans

On Thu, Feb 5, 2015 at 8:14 AM, Tom Stellard <tom at stellard.net> wrote:
> Hi Hans,
>
> Is this patch OK to merge to the 3.6 branch?
>
> I am the code owner and I approve this patch.
>
> -Tom
>
> On Thu, Feb 05, 2015 at 03:32:18PM -0000, Tom Stellard wrote:
>> Author: tstellar
>> Date: Thu Feb  5 09:32:18 2015
>> New Revision: 228303
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=228303&view=rev
>> Log:
>> R600/SI: Fix bug in TTI loop unrolling preferences
>>
>> We should be setting UnrollingPreferences::MaxCount to MAX_UINT instead
>> of UnrollingPreferences::Count.
>>
>> Count is a 'forced unrolling factor', while MaxCount sets an upper
>> limit to the unrolling factor.
>>
>> Setting Count to MAX_UINT was causing the loop in the testcase to be
>> unrolled 15 times, when it only had a maximum of 4 iterations.
>>
>> Added:
>>     llvm/trunk/test/CodeGen/R600/tti-unroll-prefs.ll
>> Modified:
>>     llvm/trunk/lib/Target/R600/AMDGPUTargetTransformInfo.cpp
>>
>> Modified: llvm/trunk/lib/Target/R600/AMDGPUTargetTransformInfo.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/R600/AMDGPUTargetTransformInfo.cpp?rev=228303&r1=228302&r2=228303&view=diff
>> ==============================================================================
>> --- llvm/trunk/lib/Target/R600/AMDGPUTargetTransformInfo.cpp (original)
>> +++ llvm/trunk/lib/Target/R600/AMDGPUTargetTransformInfo.cpp Thu Feb  5 09:32:18 2015
>> @@ -30,7 +30,7 @@ using namespace llvm;
>>  void AMDGPUTTIImpl::getUnrollingPreferences(Loop *L,
>>                                              TTI::UnrollingPreferences &UP) {
>>    UP.Threshold = 300; // Twice the default.
>> -  UP.Count = UINT_MAX;
>> +  UP.MaxCount = UINT_MAX;
>>    UP.Partial = true;
>>
>>    // TODO: Do we want runtime unrolling?
>>
>> Added: llvm/trunk/test/CodeGen/R600/tti-unroll-prefs.ll
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/R600/tti-unroll-prefs.ll?rev=228303&view=auto
>> ==============================================================================
>> --- llvm/trunk/test/CodeGen/R600/tti-unroll-prefs.ll (added)
>> +++ llvm/trunk/test/CodeGen/R600/tti-unroll-prefs.ll Thu Feb  5 09:32:18 2015
>> @@ -0,0 +1,58 @@
>> +; RUN: opt -loop-unroll -S -mtriple=amdgcn-- -mcpu=SI %s | FileCheck %s
>> +
>> +; This IR comes from this OpenCL C code:
>> +;
>> +; if (b + 4 > a) {
>> +;   for (int i = 0; i < 4; i++, b++) {
>> +;     if (b + 1 <= a)
>> +;       *(dst + c + b) = 0;
>> +;     else
>> +;       break;
>> +;   }
>> +; }
>> +;
>> +; This test is meant to check that this loop isn't unrolled into more than
>> +; four iterations.  The loop unrolling preferences we currently use cause this
>> +; loop to not be unrolled at all, but that may change in the future.
>> +
>> +; CHECK-LABEL: @test
>> +; CHECK: store i8 0, i8 addrspace(1)*
>> +; CHECK-NOT: store i8 0, i8 addrspace(1)*
>> +; CHECK: ret void
>> +define void @test(i8 addrspace(1)* nocapture %dst, i32 %a, i32 %b, i32 %c) {
>> +entry:
>> +  %add = add nsw i32 %b, 4
>> +  %cmp = icmp sgt i32 %add, %a
>> +  br i1 %cmp, label %for.cond.preheader, label %if.end7
>> +
>> +for.cond.preheader:                               ; preds = %entry
>> +  %cmp313 = icmp slt i32 %b, %a
>> +  br i1 %cmp313, label %if.then4.lr.ph, label %if.end7.loopexit
>> +
>> +if.then4.lr.ph:                                   ; preds = %for.cond.preheader
>> +  %0 = sext i32 %c to i64
>> +  br label %if.then4
>> +
>> +if.then4:                                         ; preds = %if.then4.lr.ph, %if.then4
>> +  %i.015 = phi i32 [ 0, %if.then4.lr.ph ], [ %inc, %if.then4 ]
>> +  %b.addr.014 = phi i32 [ %b, %if.then4.lr.ph ], [ %add2, %if.then4 ]
>> +  %add2 = add nsw i32 %b.addr.014, 1
>> +  %1 = sext i32 %b.addr.014 to i64
>> +  %add.ptr.sum = add nsw i64 %1, %0
>> +  %add.ptr5 = getelementptr inbounds i8 addrspace(1)* %dst, i64 %add.ptr.sum
>> +  store i8 0, i8 addrspace(1)* %add.ptr5, align 1
>> +  %inc = add nsw i32 %i.015, 1
>> +  %cmp1 = icmp slt i32 %inc, 4
>> +  %cmp3 = icmp slt i32 %add2, %a
>> +  %or.cond = and i1 %cmp3, %cmp1
>> +  br i1 %or.cond, label %if.then4, label %for.cond.if.end7.loopexit_crit_edge
>> +
>> +for.cond.if.end7.loopexit_crit_edge:              ; preds = %if.then4
>> +  br label %if.end7.loopexit
>> +
>> +if.end7.loopexit:                                 ; preds = %for.cond.if.end7.loopexit_crit_edge, %for.cond.preheader
>> +  br label %if.end7
>> +
>> +if.end7:                                          ; preds = %if.end7.loopexit, %entry
>> +  ret void
>> +}
>>
>>
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