[llvm] r260729 - [LoopRotate] Don't perform loop rotation if the loop header calls a convergent function.

[Justin Lebar via llvm-commits]

Author: jlebar
Date: Fri Feb 12 15:01:33 2016
New Revision: 260729

URL: http://llvm.org/viewvc/llvm-project?rev=260729&view=rev
Log:
[LoopRotate] Don't perform loop rotation if the loop header calls a convergent function.

Summary:
Calls to convergent functions can be duplicated, but only if the
duplicates are not control-flow dependent on any additional values.
Loop rotation doesn't meet the bar.

Reviewers: jingyue

Subscribers: mzolotukhin, llvm-commits, arsenm, joker.eph, resistor, tra, hfinkel, broune

Differential Revision: http://reviews.llvm.org/D17127

Added:
    llvm/trunk/test/Transforms/LoopRotate/convergent.ll
Modified:
    llvm/trunk/lib/Transforms/Scalar/LoopRotation.cpp

Modified: llvm/trunk/lib/Transforms/Scalar/LoopRotation.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopRotation.cpp?rev=260729&r1=260728&r2=260729&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopRotation.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopRotation.cpp Fri Feb 12 15:01:33 2016
@@ -165,6 +165,11 @@ static bool rotateLoop(Loop *L, unsigned
             << " instructions: "; L->dump());
       return false;
     }
+    if (Metrics.convergent) {
+      DEBUG(dbgs() << "LoopRotation: NOT rotating - contains convergent "
+                      "instructions: "; L->dump());
+      return false;
+    }
     if (Metrics.NumInsts > MaxHeaderSize)
       return false;
   }

Added: llvm/trunk/test/Transforms/LoopRotate/convergent.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopRotate/convergent.ll?rev=260729&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/LoopRotate/convergent.ll (added)
+++ llvm/trunk/test/Transforms/LoopRotate/convergent.ll Fri Feb 12 15:01:33 2016
@@ -0,0 +1,31 @@
+; RUN: opt -S -loop-rotate < %s | FileCheck %s
+
+ at e = global i32 10
+
+declare void @f1(i32) convergent
+declare void @f2(i32)
+
+; The call to f1 in the loop header shouldn't be duplicated (meaning, loop
+; rotation shouldn't occur), because f1 is convergent.
+
+; CHECK: call void @f1
+; CHECK-NOT: call void @f1
+
+define void @test(i32 %x) {
+entry:
+  br label %loop
+
+loop:
+  %n.phi = phi i32 [ %n, %loop.fin ], [ 0, %entry ]
+  call void @f1(i32 %n.phi)
+  %cond = icmp eq i32 %n.phi, %x
+  br i1 %cond, label %exit, label %loop.fin
+
+loop.fin:
+  %n = add i32 %n.phi, 1
+  call void @f2(i32 %n)
+  br label %loop
+
+exit:
+  ret void
+}