[polly] r218412 - We do not support alias checks for base pointers defined inside the SCoP

[Tobias Grosser]

Author: grosser
Date: Wed Sep 24 16:04:29 2014
New Revision: 218412

URL: http://llvm.org/viewvc/llvm-project?rev=218412&view=rev
Log:
We do not support alias checks for base pointers defined inside the SCoP

The run-time alias check places code that involves the base pointer at the
beginning of the SCoP. This breaks if the base pointer is defined inside the
SCoP. Hence, we can only create a run-time alias check if we are sure the base
pointer is not an instruction defined inside the scop. If it is we refuse to
handle the SCoP.

This commit should unbreak most of our current LNT failures.

Differential Revision: http://reviews.llvm.org/D5483

Added:
    polly/trunk/test/ScopDetect/run_time_alias_check.ll
Modified:
    polly/trunk/lib/Analysis/ScopDetection.cpp

Modified: polly/trunk/lib/Analysis/ScopDetection.cpp
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/lib/Analysis/ScopDetection.cpp?rev=218412&r1=218411&r2=218412&view=diff
==============================================================================
--- polly/trunk/lib/Analysis/ScopDetection.cpp (original)
+++ polly/trunk/lib/Analysis/ScopDetection.cpp Wed Sep 24 16:04:29 2014
@@ -532,7 +532,7 @@ bool ScopDetection::isValidMemoryAccess(
   if (IntToPtrInst *Inst = dyn_cast<IntToPtrInst>(BaseValue))
     return invalid<ReportIntToPtr>(Context, /*Assert=*/true, Inst);
 
-  if (PollyUseRuntimeAliasChecks || IgnoreAliasing)
+  if (IgnoreAliasing)
     return true;
 
   // Check if the base pointer of the memory access does alias with
@@ -548,8 +548,26 @@ bool ScopDetection::isValidMemoryAccess(
   // alias, if -basicaa is not available. They actually do not, but as we can
   // not proof this without -basicaa we would fail. We disable this check to
   // not cause irrelevant verification failures.
-  if (!AS.isMustAlias())
+  if (!AS.isMustAlias()) {
+    if (PollyUseRuntimeAliasChecks) {
+      bool CanBuildRunTimeCheck = true;
+      // The run-time alias check places code that involves the base pointer at
+      // the beginning of the SCoP. This breaks if the base pointer is defined
+      // inside the scop. Hence, we can only create a run-time check if we are
+      // sure the base pointer is not an instruction defined inside the scop.
+      for (const auto &Ptr : AS) {
+        Instruction *Inst = dyn_cast<Instruction>(Ptr.getValue());
+        if (Inst && Context.CurRegion.contains(Inst)) {
+          CanBuildRunTimeCheck = false;
+          break;
+        }
+      }
+
+      if (CanBuildRunTimeCheck)
+        return true;
+    }
     return invalid<ReportAlias>(Context, /*Assert=*/false, &Inst, AS);
+  }
 
   return true;
 }

Added: polly/trunk/test/ScopDetect/run_time_alias_check.ll
URL: http://llvm.org/viewvc/llvm-project/polly/trunk/test/ScopDetect/run_time_alias_check.ll?rev=218412&view=auto
==============================================================================
--- polly/trunk/test/ScopDetect/run_time_alias_check.ll (added)
+++ polly/trunk/test/ScopDetect/run_time_alias_check.ll Wed Sep 24 16:04:29 2014
@@ -0,0 +1,36 @@
+; RUN: opt %loadPolly -polly-detect -polly-code-generator=isl -analyze < %s | FileCheck %s
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare float* @getNextBasePtr(float*) readnone nounwind
+
+define void @base_pointer_is_inst_inside_invariant_1(i64 %n, float* %A, float* %B) {
+entry:
+  br label %for.i
+
+for.i:
+  %indvar.i = phi i64 [ %indvar.i.next, %for.i.inc ], [ 0, %entry ]
+  br label %S1
+
+S1:
+; To get an instruction inside a region, we use a function without side
+; effects on which SCEV blocks, but for which it is still clear that the
+; return value remains invariant throughout the whole loop.
+  %ptr = call float* @getNextBasePtr(float* %A)
+  %conv = sitofp i64 %indvar.i to float
+  %arrayidx5 = getelementptr float* %ptr, i64 %indvar.i
+  store float %conv, float* %arrayidx5, align 4
+  store float 1.0, float* %B
+  br label %for.i.inc
+
+for.i.inc:
+  %indvar.i.next = add i64 %indvar.i, 1
+  %exitcond.i = icmp ne i64 %indvar.i.next, %n
+  br i1 %exitcond.i, label %for.i, label %exit
+
+exit:
+  ret void
+}
+
+; CHECK-NOT: Valid Region for Scop