[TapirLoopInfo] Fix handling of Tapir loops with loop-variant conditi…

…ons. Fixes llvm#66.

llvm/lib/Transforms/Tapir/TapirLoopInfo.cpp

@@ -416,8 +416,11 @@ Value *TapirLoopInfo::getOrCreateTripCount(PredicatedScalarEvolution &PSE,
 
   Value *ConditionEnd = Condition->getOperand(0);
   {
-    if (!L->isLoopInvariant(ConditionEnd))
+    if (!L->isLoopInvariant(ConditionEnd)) {
+      if (!L->isLoopInvariant(Condition->getOperand(1)))
+        return nullptr;
       ConditionEnd = Condition->getOperand(1);
+    }
   }
   assert(L->isLoopInvariant(ConditionEnd) &&
          "Condition end is not loop invariant.");

llvm/test/Transforms/Tapir/loop-spawning-variant-condition.ll

@@ -0,0 +1,79 @@
+; Check the loop-spawning pass's handling to loop-variant loop conditions.
+;
+; RUN: opt < %s -loop-spawning-ti -S 2>&1 | FileCheck %s --check-prefix=CHECK-ERROR
+; RUN: opt < %s -passes='loop-spawning' -S 2>&1 | FileCheck %s --check-prefix=CHECK-ERROR
+; RUN: opt < %s -licm -loop-spawning-ti -S 2>&1 | FileCheck %s
+; RUN: opt < %s -passes='function(loop(licm)),loop-spawning' -S 2>&1 | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+$_ZNK4CPMAI21delta_compressed_leafImEE3sumEv = comdat any
+
+; Function Attrs: argmemonly nounwind willreturn
+declare token @llvm.syncregion.start() #0
+
+declare dso_local i32 @__gxx_personality_v0(...)
+
+declare dso_local void @_ZNSt6vectorImSaImEEC2EmRKS0_() unnamed_addr #1 align 2
+
+define dso_local void @_ZNK4CPMAI21delta_compressed_leafImEE3sumEv() local_unnamed_addr #1 comdat align 2 personality i8* bitcast (i32 (...)* @__gxx_personality_v0 to i8*) {
+entry:
+  %syncreg = call token @llvm.syncregion.start()
+  invoke void @_ZNSt6vectorImSaImEEC2EmRKS0_()
+          to label %invoke.cont unwind label %lpad
+
+invoke.cont:                                      ; preds = %entry
+  br label %pfor.cond
+
+lpad:                                             ; preds = %entry
+  %0 = landingpad { i8*, i32 }
+          cleanup
+  unreachable
+
+pfor.cond:                                        ; preds = %pfor.inc, %invoke.cont
+  %__begin.0 = phi i64 [ %inc42, %pfor.inc ], [ 0, %invoke.cont ]
+  detach within %syncreg, label %pfor.body.entry, label %pfor.inc unwind label %lpad41.loopexit
+
+pfor.body.entry:                                  ; preds = %pfor.cond
+  br label %pfor.body
+
+pfor.body:                                        ; preds = %pfor.body.entry
+  unreachable
+
+pfor.inc:                                         ; preds = %pfor.cond
+  %inc42 = add nuw i64 %__begin.0, 1
+  %umax117 = select i1 undef, i64 undef, i64 1
+  %exitcond118.not = icmp eq i64 %inc42, %umax117
+  br i1 %exitcond118.not, label %pfor.cond.cleanup, label %pfor.cond, !llvm.loop !1
+
+pfor.cond.cleanup:                                ; preds = %pfor.inc
+  unreachable
+
+lpad41.loopexit:                                  ; preds = %pfor.cond
+  %lpad.loopexit = landingpad { i8*, i32 }
+          cleanup
+  resume { i8*, i32 } %lpad.loopexit
+}
+
+; CHECK-ERROR: Tapir loop not transformed: failed to use divide-and-conquer loop spawning.
+
+; CHECK: define dso_local void @_ZNK4CPMAI21delta_compressed_leafImEE3sumEv()
+; CHECK: invoke.cont:
+; CHECK: invoke {{.*}}void @_ZNK4CPMAI21delta_compressed_leafImEE3sumEv.outline_pfor.cond.ls1(
+
+; CHECK: define {{.*}}void @_ZNK4CPMAI21delta_compressed_leafImEE3sumEv.outline_pfor.cond.ls1(
+; CHECK: pfor.inc.ls1:
+; CHECK: %[[INC:.+]] = add nuw i64
+; CHECK: %[[CMP:.+]] = icmp eq i64 %[[INC]]
+; CHECK: br i1 %[[CMP]], label %pfor.cond.cleanup.ls1, label %pfor.cond.ls1
+
+attributes #0 = { argmemonly nounwind willreturn }
+attributes #1 = { "use-soft-float"="false" }
+
+!llvm.ident = !{!0}
+
+!0 = !{!"clang version 12.0.0 (git@github.com:OpenCilk/opencilk-project.git 6483c891d59b7ee269d7dbde7cbf3dd36b83dd69)"}
+!1 = distinct !{!1, !2, !3}
+!2 = !{!"tapir.loop.spawn.strategy", i32 1}
+!3 = !{!"llvm.loop.unroll.disable"}