[PATCH] D86085: [LoopUnswitch] Fix incorrect Modified status

[David Stenberg via Phabricator via llvm-commits]

dstenb created this revision.
dstenb added reviewers: serge-sans-paille, reames, asbirlea.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.
dstenb requested review of this revision.

When hoisting simple values out from a loop, and the optsize attribute
hindered the pass from attempting to non-trivially unswitch the loop,
the pass would return an incorrect Modified status.

This patch also fixes two other cases where false was returned instead
of Changed. I have not added reproducers for those two cases.

This was caught using the check introduced by D80916 <https://reviews.llvm.org/D80916>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D86085

Files:
  llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
  llvm/test/Transforms/LoopUnswitch/optsize-hoist-modified.ll


Index: llvm/test/Transforms/LoopUnswitch/optsize-hoist-modified.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/LoopUnswitch/optsize-hoist-modified.ll
@@ -0,0 +1,41 @@
+; RUN: opt -loop-unswitch -enable-new-pm=0 %s -S | FileCheck %s
+
+; When hoisting simple values out from a loop, and not being able to attempt to
+; non-trivally unswitch the loop, due to the optsize attribute, the pass would
+; return an incorrect Modified status.
+
+; CHECK-LABEL: entry:
+; CHECK-NEXT: %0 = call i32 @llvm.objectsize.i32.p0i8(i8* bitcast (%struct.anon* @b to i8*), i1 false, i1 false, i1 false)
+; CHECK-NEXT: %1 = icmp uge i32 %0, 1
+; CHECK-NEXT: br label %for.cond
+
+%struct.anon = type { i16 }
+
+ at b = global %struct.anon zeroinitializer, align 1
+ at .src = private unnamed_addr constant [4 x i8] c"foo\00", align 1
+ at 0 = private unnamed_addr constant { i16, i16, [4 x i8] } { i16 0, i16 9, [4 x i8] c"bar\00" }
+ at 1 = private unnamed_addr global { { [4 x i8]*, i32, i32 }, { i16, i16, [4 x i8] }*, i8, i8 } { { [4 x i8]*, i32, i32 } { [4 x i8]* @.src, i32 5, i32 13 }, { i16, i16, [4 x i8] }* @0, i8 0, i8 0 }
+
+; Function Attrs: minsize nounwind optsize
+define i16 @c() #0 {
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %cont, %entry
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.cond
+  %0 = call i32 @llvm.objectsize.i32.p0i8(i8* bitcast (%struct.anon* @b to i8*), i1 false, i1 false, i1 false)
+  %1 = icmp uge i32 %0, 1
+  br i1 %1, label %cont, label %cont
+
+cont:                                             ; preds = %for.inc
+  %2 = load i16, i16* getelementptr inbounds (%struct.anon, %struct.anon* @b, i32 0, i32 0), align 1
+  br label %for.cond
+}
+
+; Function Attrs: nounwind readnone speculatable willreturn
+declare i32 @llvm.objectsize.i32.p0i8(i8*, i1 immarg, i1 immarg, i1 immarg) #1
+
+attributes #0 = { minsize nounwind optsize }
+attributes #1 = { nounwind readnone speculatable willreturn }
Index: llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
+++ llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
@@ -661,7 +661,7 @@
   // FIXME: Use Function::hasOptSize().
   if (OptimizeForSize ||
       LoopHeader->getParent()->hasFnAttribute(Attribute::OptimizeForSize))
-    return false;
+    return Changed;
 
   // Run through the instructions in the loop, keeping track of three things:
   //
@@ -685,10 +685,10 @@
       if (!CB)
         continue;
       if (CB->isConvergent())
-        return false;
+        return Changed;
       if (auto *II = dyn_cast<InvokeInst>(&I))
         if (!II->getUnwindDest()->canSplitPredecessors())
-          return false;
+          return Changed;
       if (auto *II = dyn_cast<IntrinsicInst>(&I))
         if (II->getIntrinsicID() == Intrinsic::experimental_guard)
           Guards.push_back(II);


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