[PATCH] D17127: [LoopRotate] Don't perform loop rotation if the loop header calls a convergent function.

[Justin Lebar via llvm-commits]

jlebar created this revision.
jlebar added a reviewer: jingyue.
jlebar added subscribers: broune, hfinkel, tra, resistor, joker.eph, arsenm, llvm-commits.
Herald added a subscriber: mzolotukhin.

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.

http://reviews.llvm.org/D17127

Files:
  lib/Transforms/Scalar/LoopRotation.cpp
  test/Transforms/LoopRotate/convergent.ll

Index: test/Transforms/LoopRotate/convergent.ll
===================================================================
--- /dev/null
+++ test/Transforms/LoopRotate/convergent.ll
@@ -0,0 +1,32 @@
+; 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() {
+entry:
+  %end = load i32, i32* @e
+  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, %end
+  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
+}
Index: lib/Transforms/Scalar/LoopRotation.cpp
===================================================================
--- lib/Transforms/Scalar/LoopRotation.cpp
+++ lib/Transforms/Scalar/LoopRotation.cpp
@@ -165,6 +165,11 @@
             << " 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;
   }


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