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

[Tom Stellard]

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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