Disable loop unswitching for some patterns containing equality comparison with undef.

This is a workaround for the bug described in PR31652 and
http://lists.llvm.org/pipermail/llvm-dev/2017-July/115497.html. The temporary
solution is to add a function EqualityPropUnSafe. In EqualityPropUnSafe, for
some simple patterns we can know the equality comparison may contains undef,
so we regard such comparison as unsafe and will not do loop-unswitching for
them. We also need to disable the select simplification when one of select
operand is undef and its result feeds into equality comparison.

The patch cannot clear the safety issue caused by the bug, but it can suppress
the issue from happening to some extent.

Differential Revision: https://reviews.llvm.org/D35811

llvm-svn: 309059

1 files changed, 121 insertions, 0 deletions

diff --git a/llvm/test/Transforms/LoopUnswitch/unswitch-equality-undef.ll b/llvm/test/Transforms/LoopUnswitch/unswitch-equality-undef.ll
new file mode 100644
index 00000000000..d77de7bd571
--- /dev/null
+++ b/llvm/test/Transforms/LoopUnswitch/unswitch-equality-undef.ll
@@ -0,0 +1,121 @@
+; RUN: opt < %s -instcombine -licm -loop-unswitch -loop-unswitch-threshold=1000 -disable-output -stats 2>&1| FileCheck %s
+; Check no loop unswitch is done because unswitching of equality expr with
+; undef is unsafe before the freeze patch is committed.
+; CHECK-NOT: Number of branches unswitched
+
+define void @ham(i64 %arg) local_unnamed_addr {
+bb:
+  %tmp = icmp eq i64 %arg, 0
+  br i1 %tmp, label %bb3, label %bb1
+
+bb1:                                              ; preds = %bb
+  %tmp2 = load volatile i64, i64* @global, align 8
+  br label %bb3
+
+bb3:                                              ; preds = %bb1, %bb
+  %tmp4 = phi i64 [ %tmp2, %bb1 ], [ undef, %bb ]
+  %tmp5 = load i64, i64* @global.1, align 8
+  br label %bb6
+
+bb6:                                              ; preds = %bb21, %bb3
+  %tmp7 = phi i64 [ 3, %bb21 ], [ %tmp5, %bb3 ]
+  %tmp8 = phi i64 [ %tmp25, %bb21 ], [ 0, %bb3 ]
+  %tmp9 = icmp eq i64 %tmp7, %arg
+  br i1 %tmp9, label %bb10, label %bb28
+
+bb10:                                             ; preds = %bb6
+  %tmp11 = icmp eq i64 %tmp7, 0
+  br i1 %tmp11, label %bb21, label %bb12
+
+bb12:                                             ; preds = %bb10
+  %tmp13 = load i64, i64* @global.2, align 8
+  %tmp14 = add nsw i64 %tmp13, 1
+  store i64 %tmp14, i64* @global.2, align 8
+  %tmp15 = load i64, i64* @global.3, align 8
+  %tmp16 = icmp eq i64 %tmp15, %tmp4
+  br i1 %tmp16, label %bb17, label %bb21
+
+bb17:                                             ; preds = %bb12
+  %tmp18 = phi i64 [ %tmp15, %bb12 ]
+  %tmp19 = load i64, i64* @global.4, align 8
+  %tmp20 = add nsw i64 %tmp19, %tmp18
+  store i64 %tmp20, i64* @global.5, align 8
+  br label %bb29
+
+bb21:                                             ; preds = %bb12, %bb10
+  %tmp22 = load i64, i64* @global.3, align 8
+  %tmp23 = load volatile i64, i64* @global, align 8
+  %tmp24 = add nsw i64 %tmp23, %tmp22
+  store i64 %tmp24, i64* @global.5, align 8
+  store i64 3, i64* @global.1, align 8
+  %tmp25 = add nsw i64 %tmp8, 1
+  %tmp26 = load i64, i64* @global.6, align 8
+  %tmp27 = icmp slt i64 %tmp25, %tmp26
+  br i1 %tmp27, label %bb6, label %bb28
+
+bb28:                                             ; preds = %bb21, %bb6
+  br label %bb29
+
+bb29:                                             ; preds = %bb28, %bb17
+  ret void
+}
+
+define void @zot(i64 %arg, i64 %arg1) local_unnamed_addr {
+bb:
+  %tmp = icmp eq i64 %arg, 0
+  %tmp2 = select i1 %tmp, i64 %arg1, i64 undef
+  %tmp3 = load i64, i64* @global.1, align 8
+  br label %bb4
+
+bb4:                                              ; preds = %bb19, %bb
+  %tmp5 = phi i64 [ 3, %bb19 ], [ %tmp3, %bb ]
+  %tmp6 = phi i64 [ %tmp23, %bb19 ], [ 0, %bb ]
+  %tmp7 = icmp eq i64 %tmp5, %arg
+  br i1 %tmp7, label %bb8, label %bb26
+
+bb8:                                              ; preds = %bb4
+  %tmp9 = icmp eq i64 %tmp5, 0
+  br i1 %tmp9, label %bb19, label %bb10
+
+bb10:                                             ; preds = %bb8
+  %tmp11 = load i64, i64* @global.2, align 8
+  %tmp12 = add nsw i64 %tmp11, 1
+  store i64 %tmp12, i64* @global.2, align 8
+  %tmp13 = load i64, i64* @global.3, align 8
+  %tmp14 = icmp eq i64 %tmp13, %tmp2
+  br i1 %tmp14, label %bb15, label %bb19
+
+bb15:                                             ; preds = %bb10
+  %tmp16 = phi i64 [ %tmp13, %bb10 ]
+  %tmp17 = load i64, i64* @global.4, align 8
+  %tmp18 = add nsw i64 %tmp17, %tmp16
+  store i64 %tmp18, i64* @global.5, align 8
+  br label %bb27
+
+bb19:                                             ; preds = %bb10, %bb8
+  %tmp20 = load i64, i64* @global.3, align 8
+  %tmp21 = load volatile i64, i64* @global, align 8
+  %tmp22 = add nsw i64 %tmp21, %tmp20
+  store i64 %tmp22, i64* @global.5, align 8
+  store i64 3, i64* @global.1, align 8
+  %tmp23 = add nsw i64 %tmp6, 1
+  %tmp24 = load i64, i64* @global.6, align 8
+  %tmp25 = icmp slt i64 %tmp23, %tmp24
+  br i1 %tmp25, label %bb4, label %bb26
+
+bb26:                                             ; preds = %bb19, %bb4
+  br label %bb27
+
+bb27:                                             ; preds = %bb26, %bb15
+  ret void
+}
+
+@global = common global i64 0, align 8
+@global.1 = common global i64 0, align 8
+@global.2 = common global i64 0, align 8
+@global.3 = common global i64 0, align 8
+@global.4 = common global i64 0, align 8
+@global.5 = common global i64 0, align 8
+@global.6 = common global i64 0, align 8
+
+