[ADCE][Dominators] Reapply: Teach ADCE to preserve dominators

Summary:
This patch teaches ADCE to preserve both DominatorTrees and PostDominatorTrees.

This is reapplies the original patch r311057 that was reverted in r311381.
The previous version wasn't using the batch update api for updating dominators,
which in vary rare cases caused assertion failures.

This also fixes PR34258.

Reviewers: dberlin, chandlerc, sanjoy, davide, grosser, brzycki

Reviewed By: davide

Subscribers: grandinj, zhendongsu, llvm-commits, david2050

Differential Revision: https://reviews.llvm.org/D35869

llvm-svn: 311467

3 files changed, 81 insertions, 0 deletions

diff --git a/llvm/test/Transforms/ADCE/2017-08-21-DomTree-deletions.ll b/llvm/test/Transforms/ADCE/2017-08-21-DomTree-deletions.ll
new file mode 100644
index 00000000000..e532f29e9f4
--- /dev/null
+++ b/llvm/test/Transforms/ADCE/2017-08-21-DomTree-deletions.ll
@@ -0,0 +1,24 @@
+; RUN: opt < %s -adce | llvm-dis
+; RUN: opt < %s -adce -verify-dom-info | llvm-dis
+
+define void @foo() {
+entry:
+  br label %switch
+switch:                    ; preds = %entry
+  switch i32 undef, label %default [
+    i32 2, label %two
+    i32 5, label %five
+    i32 4, label %four
+  ]
+four:                      ; preds = %switch
+  br label %exit
+five:                      ; preds = %switch
+  br label %exit
+two:                       ; preds = %switch
+  br label %exit
+default:                   ; preds = %switch
+  br label %exit
+exit:                      ; preds = %default, %two, %five, %four
+  ret void
+}
+
diff --git a/llvm/test/Transforms/ADCE/domtree-DoubleDeletion.ll b/llvm/test/Transforms/ADCE/domtree-DoubleDeletion.ll
new file mode 100644
index 00000000000..018eb79b26f
--- /dev/null
+++ b/llvm/test/Transforms/ADCE/domtree-DoubleDeletion.ll
@@ -0,0 +1,39 @@
+; RUN: opt < %s -gvn -simplifycfg -adce | llvm-dis
+; RUN: opt < %s -gvn -simplifycfg -adce -verify-dom-info | llvm-dis
+
+; This test makes sure that the DominatorTree properly handles
+; deletion of edges that go to forward-unreachable regions.
+; In this case, %land.end is already forward unreachable when
+; the DT gets informed about the deletion of %entry -> %land.end.
+
+@a = common global i32 0, align 4
+
+define i32 @main() {
+entry:
+  %retval = alloca i32, align 4
+  store i32 0, i32* %retval, align 4
+  %0 = load i32, i32* @a, align 4
+  %cmp = icmp ne i32 %0, 1
+  br i1 %cmp, label %land.rhs, label %land.end4
+
+land.rhs:                                         ; preds = %entry
+  %1 = load i32, i32* @a, align 4
+  %tobool = icmp ne i32 %1, 0
+  br i1 %tobool, label %land.rhs1, label %land.end
+
+land.rhs1:                                        ; preds = %land.rhs
+  br label %land.end
+
+land.end:                                         ; preds = %land.rhs1, %land.rhs
+  %2 = phi i1 [ false, %land.rhs ], [ true, %land.rhs1 ]
+  %land.ext = zext i1 %2 to i32
+  %conv = trunc i32 %land.ext to i16
+  %conv2 = sext i16 %conv to i32
+  %tobool3 = icmp ne i32 %conv2, 0
+  br label %land.end4
+
+land.end4:                                        ; preds = %land.end, %entry
+  %3 = phi i1 [ false, %entry ], [ %tobool3, %land.end ]
+  %land.ext5 = zext i1 %3 to i32
+  ret i32 0
+}
diff --git a/llvm/test/Transforms/ADCE/unreachable.ll b/llvm/test/Transforms/ADCE/unreachable.ll
new file mode 100644
index 00000000000..aaacc184225
--- /dev/null
+++ b/llvm/test/Transforms/ADCE/unreachable.ll
@@ -0,0 +1,18 @@
+; RUN: opt < %s -adce -simplifycfg | llvm-dis
+; RUN: opt < %s -passes=adce | llvm-dis
+
+define i32 @Test(i32 %A, i32 %B) {
+BB1:
+        br label %BB4
+
+BB2:            ; No predecessors!
+        br label %BB3
+
+BB3:            ; preds = %BB4, %BB2
+        %ret = phi i32 [ %X, %BB4 ], [ %B, %BB2 ]               ; <i32> [#uses=1]
+        ret i32 %ret
+
+BB4:            ; preds = %BB1
+        %X = phi i32 [ %A, %BB1 ]               ; <i32> [#uses=1]
+        br label %BB3
+}