[polly] r252726 - ScopDetection: Tighten the check for always executed 'error blocks'

[Tobias Grosser via llvm-commits]

Author: grosser
Date: Wed Nov 11 07:25:13 2015
New Revision: 252726

URL: http://llvm.org/viewvc/llvm-project?rev=252726&view=rev
Log:
ScopDetection: Tighten the check for always executed 'error blocks'

Basic blocks that are always executed can not be error blocks as their execution
can not possibly be an unlikely event. In this commit we tighten the check
if an error block to basic blcoks that do not dominate the exit condition, but
that dominate all exiting blocks of the scop.

Added:
    polly/trunk/test/ScopDetect/error-block-always-executed.ll
Modified:
    polly/trunk/lib/Support/ScopHelper.cpp

Modified: polly/trunk/lib/Support/ScopHelper.cpp
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/lib/Support/ScopHelper.cpp?rev=252726&r1=252725&r2=252726&view=diff
==============================================================================
--- polly/trunk/lib/Support/ScopHelper.cpp (original)
+++ polly/trunk/lib/Support/ScopHelper.cpp Wed Nov 11 07:25:13 2015
@@ -352,7 +352,14 @@ bool polly::isErrorBlock(BasicBlock &BB,
   if (LI.isLoopHeader(&BB))
     return false;
 
-  if (DT.dominates(&BB, R.getExit()))
+  // Basic blocks that are always executed are not considered error blocks,
+  // as their execution can not be a rare event.
+  bool DominatesAllPredecessors = true;
+  for (auto Pred : predecessors(R.getExit()))
+    if (R.contains(Pred) && !DT.dominates(&BB, Pred))
+      DominatesAllPredecessors = false;
+
+  if (DominatesAllPredecessors)
     return false;
 
   // FIXME: This is a simple heuristic to determine if the load is executed

Added: polly/trunk/test/ScopDetect/error-block-always-executed.ll
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/test/ScopDetect/error-block-always-executed.ll?rev=252726&view=auto
==============================================================================
--- polly/trunk/test/ScopDetect/error-block-always-executed.ll (added)
+++ polly/trunk/test/ScopDetect/error-block-always-executed.ll Wed Nov 11 07:25:13 2015
@@ -0,0 +1,62 @@
+; RUN: opt %loadPolly -polly-code-generator=isl -polly-detect -analyze < %s \
+; RUN:     | FileCheck %s
+;
+; CHECK-NOT: Valid Region for Scop:
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+%struct.hoge = type { i32, i32, i32, i32 }
+
+; Function Attrs: nounwind uwtable
+define void @widget() #0 {
+bb13:
+  %tmp1 = alloca %struct.hoge, align 4
+  br i1 undef, label %bb14, label %bb19
+
+bb14:                                             ; preds = %bb13
+  %tmp = load i32, i32* undef, align 4, !tbaa !1
+  call void @quux() #2
+  br i1 false, label %bb15, label %bb18
+
+bb15:                                             ; preds = %bb14
+  %tmp16 = getelementptr inbounds %struct.hoge, %struct.hoge* %tmp1, i64 0, i32 1
+  %tmp17 = getelementptr inbounds %struct.hoge, %struct.hoge* %tmp1, i64 0, i32 2
+  br label %bb19
+
+bb18:                                             ; preds = %bb14
+  br label %bb19
+
+bb19:                                             ; preds = %bb18, %bb15, %bb13
+  %tmp20 = phi i32 [ undef, %bb13 ], [ %tmp, %bb15 ], [ %tmp, %bb18 ]
+  unreachable
+
+bb21:                                             ; preds = %bb8
+  unreachable
+
+bb22:                                             ; preds = %bb8, %bb8, %bb8, %bb8
+  br label %bb23
+
+bb23:                                             ; preds = %bb22
+  unreachable
+
+bb24:                                             ; preds = %bb8, %bb8
+  unreachable
+
+bb25:                                             ; preds = %bb2
+  unreachable
+}
+
+declare void @quux() #1
+
+attributes #0 = { nounwind uwtable "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #1 = { "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="false" "no-infs-fp-math"="false" "no-nans-fp-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2" "unsafe-fp-math"="false" "use-soft-float"="false" }
+attributes #2 = { nounwind }
+
+!llvm.ident = !{!0}
+
+!0 = !{!"clang version 3.8.0 (trunk 252700) (llvm/trunk 252705)"}
+!1 = !{!2, !2, i64 0}
+!2 = !{!"int", !3, i64 0}
+!3 = !{!"omnipotent char", !4, i64 0}
+!4 = !{!"Simple C/C++ TBAA"}