[PATCH] D32674: [LoopIdiom] PR32811 check for safety while expanding

[Aditya Kumar via Phabricator via llvm-commits]

hiraditya updated this revision to Diff 97206.

https://reviews.llvm.org/D32674

Files:
  lib/Transforms/Scalar/LoopIdiomRecognize.cpp
  test/Transforms/LoopIdiom/unsafe.ll


Index: test/Transforms/LoopIdiom/unsafe.ll
===================================================================
--- /dev/null
+++ test/Transforms/LoopIdiom/unsafe.ll
@@ -0,0 +1,33 @@
+; RUN: opt -S < %s -loop-idiom | FileCheck %s
+; CHECK-NOT: memset
+; check that memset is not generated (for assignment in for.body5) because that will result
+; in udiv hoisted out of the loop by the SCEV Expander
+; TODO: ideally we should be able to generate memset
+; if SCEV expander is taught to generate the dependencies
+; at the right point.
+
+ at a = global i32 0, align 4
+ at b = global i32 0, align 4
+ at c = external local_unnamed_addr global [1 x i8], align 1
+
+define void @main() local_unnamed_addr {
+entry:
+  %d0 = load i32, i32* @a, align 4
+  %d1 = load i32, i32* @b, align 4
+  br label %for.cond1thread-pre-split
+
+for.cond1thread-pre-split:                        ; preds = %for.body5, %entry
+  %div = udiv i32 %d0, %d1
+  br label %for.body5
+
+for.body5:                                        ; preds = %for.body5, %for.cond1thread-pre-split
+  %indvars.iv = phi i64 [ undef, %for.cond1thread-pre-split ], [ %indvars.iv.next, %for.body5 ]
+  %divx = sext i32 %div to i64
+  %0 = add nsw i64 %divx, %indvars.iv
+  %arrayidx = getelementptr inbounds [1 x i8], [1 x i8]* @c, i64 0, i64 %0
+  store i8 0, i8* %arrayidx, align 1
+  %indvars.iv.next = add nsw i64 %indvars.iv, 1
+  %1 = trunc i64 %indvars.iv.next to i32
+  %tobool4 = icmp eq i32 %1, 0
+  br i1 %tobool4, label %for.cond1thread-pre-split, label %for.body5
+}
Index: lib/Transforms/Scalar/LoopIdiomRecognize.cpp
===================================================================
--- lib/Transforms/Scalar/LoopIdiomRecognize.cpp
+++ lib/Transforms/Scalar/LoopIdiomRecognize.cpp
@@ -783,6 +783,11 @@
   if (NegStride)
     Start = getStartForNegStride(Start, BECount, IntPtr, StoreSize, SE);
 
+  // TODO: ideally we should still be able to generate memset if SCEV expander
+  // is taught to generate the dependencies at the latest point.
+  if (!isSafeToExpand(Start, *SE))
+    return false;
+
   // Okay, we have a strided store "p[i]" of a splattable value.  We can turn
   // this into a memset in the loop preheader now if we want.  However, this
   // would be unsafe to do if there is anything else in the loop that may read


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