[llvm] r244448 - Prevent the scalarizer from caching incorrect entries

[Fraser Cormack via llvm-commits]

Author: fcormack
Date: Mon Aug 10 09:48:47 2015
New Revision: 244448

URL: http://llvm.org/viewvc/llvm-project?rev=244448&view=rev
Log:
Prevent the scalarizer from caching incorrect entries

The scalarizer can cache incorrect entries when walking up a chain of
insertelement instructions. This occurs when it encounters more than one
instruction that it is not actively searching for, as it unconditionally caches
every element it finds. The fix is to only cache the first element that it
isn't searching for so we don't overwrite correct entries.

Reviewers: hfinkel

Differential Revision: http://reviews.llvm.org/D11559

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

Modified: llvm/trunk/lib/Transforms/Scalar/Scalarizer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/Scalarizer.cpp?rev=244448&r1=244447&r2=244448&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/Scalarizer.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/Scalarizer.cpp Mon Aug 10 09:48:47 2015
@@ -227,10 +227,16 @@ Value *Scatterer::operator[](unsigned I)
       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));

Added: llvm/trunk/test/Transforms/Scalarizer/cache-bug.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/Scalarizer/cache-bug.ll?rev=244448&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/Scalarizer/cache-bug.ll (added)
+++ llvm/trunk/test/Transforms/Scalarizer/cache-bug.ll Mon Aug 10 09:48:47 2015
@@ -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
+}