[PATCH] D11559: Prevent the scalarizer from caching incorrect entries

[Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL244448: Prevent the scalarizer from caching incorrect entries (authored by fcormack).

Changed prior to commit:
  http://reviews.llvm.org/D11559?vs=30803&id=31668#toc

Repository:
  rL LLVM

http://reviews.llvm.org/D11559

Files:
  llvm/trunk/lib/Transforms/Scalar/Scalarizer.cpp
  llvm/trunk/test/Transforms/Scalarizer/cache-bug.ll

Index: llvm/trunk/test/Transforms/Scalarizer/cache-bug.ll
===================================================================
--- llvm/trunk/test/Transforms/Scalarizer/cache-bug.ll
+++ llvm/trunk/test/Transforms/Scalarizer/cache-bug.ll
@@ -0,0 +1,30 @@
+; RUN: opt -scalarizer -S < %s | FileCheck %s
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+
+
+; Check that vector element 1 is scalarized correctly from a chain of
+; insertelement instructions
+define void @func(i32 %x) {
+; CHECK-LABEL: @func(
+; CHECK-NOT: phi i32 [ %x, %entry ], [ %inc.pos.y, %loop ]
+; CHECK:     phi i32 [ %inc, %entry ], [ %inc.pos.y, %loop ]
+; CHECK:   ret void
+entry:
+  %vecinit = insertelement <2 x i32> <i32 0, i32 0>, i32 %x, i32 1
+  %inc = add i32 %x, 1
+  %0 = insertelement <2 x i32> %vecinit, i32 %inc, i32 1
+  br label %loop
+
+loop:
+  %pos = phi <2 x i32> [ %0, %entry ], [ %new.pos.y, %loop ]
+  %i = phi i32 [ 0, %entry ], [ %new.i, %loop ]
+  %pos.y = extractelement <2 x i32> %pos, i32 1
+  %inc.pos.y = add i32 %pos.y, 1
+  %new.pos.y = insertelement <2 x i32> %pos, i32 %inc.pos.y, i32 1
+  %new.i = add i32 %i, 1
+  %cmp2 = icmp slt i32 %new.i, 1
+  br i1 %cmp2, label %loop, label %exit
+
+exit:
+  ret void
+}
Index: llvm/trunk/lib/Transforms/Scalar/Scalarizer.cpp
===================================================================
--- llvm/trunk/lib/Transforms/Scalar/Scalarizer.cpp
+++ llvm/trunk/lib/Transforms/Scalar/Scalarizer.cpp
@@ -227,10 +227,16 @@
       if (!Idx)
         break;
       unsigned J = Idx->getZExtValue();
-      CV[J] = Insert->getOperand(1);
       V = Insert->getOperand(0);
-      if (I == J)
+      if (I == J) {
+        CV[J] = Insert->getOperand(1);
         return CV[J];
+      } else if (!CV[J]) {
+        // Only cache the first entry we find for each index we're not actively
+        // searching for. This prevents us from going too far up the chain and
+        // caching incorrect entries.
+        CV[J] = Insert->getOperand(1);
+      }
     }
     CV[I] = Builder.CreateExtractElement(V, Builder.getInt32(I),
                                          V->getName() + ".i" + Twine(I));


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