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

[Tom Stellard]

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
+}