[PATCH] D23572: [SCEV] Postpone ScalarEvolution::forgetLoop after TripCountSC is expanded when unroll runtime iteration loop

[Wei Mi via llvm-commits]

wmi created this revision.
wmi added a reviewer: sanjoy.
wmi added subscribers: llvm-commits, davidxl, mkuper.
wmi set the repository for this revision to rL LLVM.
Herald added a subscriber: sanjoy.

In llvm::UnrollRuntimeLoopRemainder, if the loop to be unrolled is the inner loop inside a loop nest, the scalar evolution needs to be dropped for its parent loop which is done by ScalarEvolution::forgetLoop. However, we can postpone forgetLoop to the end of UnrollRuntimeLoopRemainder so TripCountSC expansion can still reuse existing value.     

Repository:
  rL LLVM

https://reviews.llvm.org/D23572

Files:
  lib/Transforms/Utils/LoopUnrollRuntime.cpp
  test/Analysis/ScalarEvolution/scev-expander-existing-value.ll

Index: test/Analysis/ScalarEvolution/scev-expander-existing-value.ll
===================================================================
--- test/Analysis/ScalarEvolution/scev-expander-existing-value.ll
+++ test/Analysis/ScalarEvolution/scev-expander-existing-value.ll
@@ -1,12 +1,15 @@
-; RUN: opt < %s -loop-vectorize -force-vector-width=4 -verify-scev-maps -S |FileCheck %s
+; RUN: opt < %s -loop-vectorize -force-vector-width=4 -verify-scev-maps -S |FileCheck %s --check-prefix=VEC
+; RUN: opt < %s -loop-unroll -unroll-runtime -unroll-count=2 -verify-scev-maps -S | FileCheck %s --check-prefix=UNROLL
 
 ; SCEV expansion uses existing value when the SCEV has no AddRec expr.
-; CHECK: select
-; CHECK-NOT: select
+; VEC-LABEL: @foo_vect(
+; VEC: select
+; VEC-NOT: select
+; VEC: ret
 
 @a = common global [1000 x i16] zeroinitializer, align 16
 
-define i32 @foo(i32 %x, i32 %y) {
+define i32 @foo_vect(i32 %x, i32 %y) {
 entry:
   %cmp = icmp slt i32 %x, %y
   %cond = select i1 %cmp, i32 %x, i32 %y
@@ -36,3 +39,37 @@
   %total.0.lcssa = phi i32 [ 0, %entry ], [ %add.lcssa, %for.end.loopexit ]
   ret i32 %total.0.lcssa
 }
+
+; Check SCEV expansion uses existing value when unrolling an inner loop with runtime trip count in a loop nest.
+; UNROLL-LABEL: @foo_unroll(
+; UNROLL: select
+; UNROLL-NOT: select
+; UNROLL: ret
+
+define void @foo_unroll(i32 %xfL, i32 %scaleL) local_unnamed_addr {
+entry:
+  br label %for.body
+
+for.body:                                         ; preds = %for.body5, %for.body, %entry
+  %xfL.addr.033 = phi i32 [ %xfL, %entry ], [ %add, %for.body5 ]
+  %add = add nsw i32 %xfL.addr.033, %scaleL
+  %shr = ashr i32 %add, 16
+  %cmp.i = icmp slt i32 0, %shr
+  %.sroa.speculated = select i1 %cmp.i, i32 0, i32 %shr
+  %cmp425 = icmp slt i32 0, %.sroa.speculated
+  br i1 %cmp425, label %for.body5.preheader, label %for.end
+
+for.body5.preheader:                              ; preds = %for.body
+  %tmp0 = sext i32 %.sroa.speculated to i64
+  br label %for.body5
+
+for.body5:                                        ; preds = %for.body5, %for.body5.preheader
+  %indvars.iv = phi i64 [ 0, %for.body5.preheader ], [ %indvars.iv.next, %for.body5 ]
+  %indvars.iv.next = add nsw i64 %indvars.iv, 1
+  %cmp4 = icmp slt i64 %indvars.iv.next, %tmp0
+  br i1 %cmp4, label %for.body5, label %for.body
+
+for.end:
+  ret void
+}
+
Index: lib/Transforms/Utils/LoopUnrollRuntime.cpp
===================================================================
--- lib/Transforms/Utils/LoopUnrollRuntime.cpp
+++ lib/Transforms/Utils/LoopUnrollRuntime.cpp
@@ -491,11 +491,6 @@
   if (Log2_32(Count) > BEWidth)
     return false;
 
-  // If this loop is nested, then the loop unroller changes the code in the
-  // parent loop, so the Scalar Evolution pass needs to be run again.
-  if (Loop *ParentLoop = L->getParentLoop())
-    SE->forgetLoop(ParentLoop);
-
   BasicBlock *Latch = L->getLoopLatch();
 
   // Loop structure is the following:
@@ -685,6 +680,12 @@
     ConnectProlog(L, BECount, Count, PrologExit, PreHeader, NewPreHeader,
                   VMap, DT, LI, PreserveLCSSA);
   }
+
+  // If this loop is nested, then the loop unroller changes the code in the
+  // parent loop, so the Scalar Evolution pass needs to be run again.
+  if (Loop *ParentLoop = L->getParentLoop())
+    SE->forgetLoop(ParentLoop);
+
   NumRuntimeUnrolled++;
   return true;
 }


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D23572.68207.patch
Type: text/x-patch
Size: 3387 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20160816/800b2f07/attachment.bin>