[PATCH] D15559: [LoopUnrollRuntime] Do unroll when IV's setp is one or minus one

[Junmo Park via llvm-commits]

flyingforyou retitled this revision from "[LoopUnrollRuntime]  Do unroll when the unroll factor is 2" to "[LoopUnrollRuntime] Do unroll when IV's setp is one or minus one".
flyingforyou updated the summary for this revision.
flyingforyou updated this revision to Diff 43408.
flyingforyou added a comment.

Current algorithm doesn't care about where does trip count's division come from. 
That means, if TripCount is divided by some value in loop's preheader, compiler will give up doing unrolling. (Even if IV's step is one or minus one.)

If IV's step is constant likes one or minus one or multiple of 2, we don't need to generate division for computing trip count.

I tested this patch on r256132 with test-suite, spec2000,2006, commercial benchmarks. There is no regression on Cortex-A57.

I hope that this patch is acceptable for everybody.

Junmo.


http://reviews.llvm.org/D15559

Files:
  lib/Transforms/Utils/LoopUnrollRuntime.cpp
  test/Transforms/LoopUnroll/high-cost-trip-count-computation.ll

Index: test/Transforms/LoopUnroll/high-cost-trip-count-computation.ll
===================================================================
--- test/Transforms/LoopUnroll/high-cost-trip-count-computation.ll
+++ test/Transforms/LoopUnroll/high-cost-trip-count-computation.ll
@@ -24,4 +24,47 @@
   ret i32 0
 }
 
+;; We expect this loop to be unrolled, because IV's step is minus one.
+;; So we don't need to generate division for computing trip count.
+
+define i32 @test2(i64 %v12, i8* %array, i64* %loc, fp128 %call1.i, fp128 %call2.i) {
+; CHECK-LABEL: @test2(
+; CHECK-LABEL: for.body.prol
+; CHECK: 0xL0000000000000000401DFFFFFFF80000
+; CHECK: 0xL0000000000000000401DFFFFFFF80000
+; CHECK: 0xL0000000000000000401DFFFFFFF80000
+entry:
+  %rem0 = load i64, i64* %loc, align 8, !tbaa !0
+  %div1 = fdiv fast fp128 %call1.i, %call2.i
+  %conv7 = fptoui fp128 %div1 to i64
+  %sub11 = add i64 %conv7, 23
+  %div11 = udiv i64 %sub11, %conv7
+  %cmp.i38 = icmp ugt i64 %div11, 1
+  %div12 = select i1 %cmp.i38, i64 %div11, i64 1
+  br label %for.body
+for.body:
+  %rem1 = phi i64 [ %rem0, %entry ], [ %rem2, %for.body ]
+  %tmp1 = phi float [ 1.000000e+00, %entry ], [ %conv21, %for.body ]
+  %sum1 = phi float [ 0.000000e+00, %entry ], [ %add18, %for.body ]
+  %k1 = phi i64 [ %div12, %entry ], [ %dec, %for.body ]
+  %mul1 = mul i64 %rem1, 48271
+  %rem2 = urem i64 %mul1, 2147483647
+  %sub16 = add nsw i64 %rem2, -1
+  %conv17. = uitofp i64 %sub16 to float
+  %mul2 = fmul fast float %conv17., %tmp1
+  %add18 = fadd fast float %mul2, %sum1
+  %conv19 = fpext float %tmp1 to fp128
+  %mul3 = fmul fast fp128 %conv19, 0xL0000000000000000401DFFFFFFF80000
+  %conv21 = fptrunc fp128 %mul3 to float
+  %dec = add i64 %k1, -1
+  %cmp = icmp eq i64 %dec, 0
+  br i1 %cmp, label %exit, label %for.body
+exit:
+  %conv22 = phi float [ %conv21, %for.body ]
+  %add19 = phi float [ %add18, %for.body ]
+  %rem3 = phi i64 [ %rem2, %for.body ]
+  store i64 %rem3, i64* %loc, align 8, !tbaa !0
+  ret i32 0
+}
+
 !0 = !{i64 1, i64 100}
Index: lib/Transforms/Utils/LoopUnrollRuntime.cpp
===================================================================
--- lib/Transforms/Utils/LoopUnrollRuntime.cpp
+++ lib/Transforms/Utils/LoopUnrollRuntime.cpp
@@ -313,6 +313,27 @@
   BasicBlock *Header = L->getHeader();
   const DataLayout &DL = Header->getModule()->getDataLayout();
   SCEVExpander Expander(*SE, DL, "loop-unroll");
+
+  // If IV's step is one or minus one, we can unroll the loop.
+  // Because we don't need to generate division for computing trip count.
+  if (BranchInst *BI =
+          dyn_cast<BranchInst>(L->getExitingBlock()->getTerminator())) {
+    if (ICmpInst *ExitCondICmp = dyn_cast<ICmpInst>(BI->getCondition())) {
+      if (const SCEVAddRecExpr *AR =
+              dyn_cast<SCEVAddRecExpr>(SE->getSCEVAtScope(
+                  SE->getSCEV(ExitCondICmp->getOperand(0)), L))) {
+        if (AR->isAffine() && AR->getOperand(1)->getSCEVType() == scConstant) {
+          if (const SCEVConstant *SCConst =
+                  cast<SCEVConstant>(AR->getOperand(1))) {
+            if (SCConst->getValue()->isOne() ||
+                SCConst->getValue()->isMinusOne())
+              AllowExpensiveTripCount = true;
+          }
+        }
+      }
+    }
+  }
+
   if (!AllowExpensiveTripCount && Expander.isHighCostExpansion(TripCountSC, L))
     return false;
 


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