[GVN PRE] Patch the source for Phi node in PRE

We must patch all existing incoming values of Phi node,
otherwise it is possible that we can see poison
where program does not expect to see it.

This is the similar what GVN does.

The added test test/Transforms/GVN/PRE/pre-jt-add.ll shows an
example of wrong optimization done by jump threading due to
GVN PRE did not patch existing incoming value.

Reviewers: mkazantsev, wmi, dberlin, davide
Reviewed By: dberlin
Subscribers: efriedma, llvm-commits
Differential Revision: https://reviews.llvm.org/D39637

llvm-svn: 317768

2 files changed, 88 insertions, 0 deletions

diff --git a/llvm/test/Transforms/GVN/PRE/pre-jt-add.ll b/llvm/test/Transforms/GVN/PRE/pre-jt-add.ll
new file mode 100644
index 00000000000..469b78cc4f1
--- /dev/null
+++ b/llvm/test/Transforms/GVN/PRE/pre-jt-add.ll
@@ -0,0 +1,36 @@
+; RUN: opt < %s -gvn -enable-pre -jump-threading -S | FileCheck %s
+
+@H = common global i32 0
+@G = common global i32 0
+
+define i32 @test(i1 %cond, i32 %v) nounwind {
+; CHECK-LABEL: @test
+entry:
+  br i1 %cond, label %bb, label %bb1
+
+bb:
+; CHECK: store
+; CHECK-NOT: br label %return
+  %add.1 = add nuw nsw i32 %v, -1
+  store i32 %add.1, i32* @G, align 4
+  br label %merge
+
+bb1:
+  br label %merge
+
+merge:
+  %add.2 = add i32 %v, -1
+  %cmp = icmp sgt i32 %add.2, 0
+  br i1 %cmp, label %action, label %return
+
+action:
+; CHECK: store
+; CHECK-NEXT: br label %return
+  store i32 %add.2, i32* @H, align 4
+  br label %return
+
+return:
+  %p = phi i32 [0, %merge], [1, %action]
+  ret i32 %p
+}
+
diff --git a/llvm/test/Transforms/GVN/PRE/pre-poison-add.ll b/llvm/test/Transforms/GVN/PRE/pre-poison-add.ll
new file mode 100644
index 00000000000..61dfda507a5
--- /dev/null
+++ b/llvm/test/Transforms/GVN/PRE/pre-poison-add.ll
@@ -0,0 +1,52 @@
+; RUN: opt < %s -gvn -enable-pre -S | FileCheck %s
+
+@H = common global i32 0
+@G = common global i32 0
+
+define i32 @test1(i1 %cond, i32 %v) nounwind {
+; CHECK-LABEL: @test1
+entry:
+    br i1 %cond, label %bb, label %bb1
+
+bb:
+    %add.1 = add nuw nsw i32 %v, 42
+; CHECK: %add.1 = add i32 %v, 42
+    store i32 %add.1, i32* @G, align 4
+    br label %return
+
+bb1:
+; CHECK: %.pre = add i32 %v, 42
+    br label %return
+
+return:
+; CHECK: %add.2.pre-phi = phi i32 [ %.pre, %bb1 ], [ %add.1, %bb ]
+; CHECK-NEXT: store i32 %add.2.pre-phi, i32* @H, align 4
+; CHECK-NEXT: ret i32 0
+    %add.2 = add i32 %v, 42
+    store i32 %add.2, i32* @H, align 4
+    ret i32 0
+}
+
+define i32 @test2(i1 %cond, i32 %v) nounwind {
+; CHECK-LABEL: @test2
+entry:
+    br i1 %cond, label %bb, label %bb1
+
+bb:
+    %add.1 = add i32 %v, 42
+; CHECK: %add.1 = add i32 %v, 42
+    store i32 %add.1, i32* @G, align 4
+    br label %return
+
+bb1:
+; CHECK: %.pre = add nuw nsw i32 %v, 42
+    br label %return
+
+return:
+; CHECK: %add.2.pre-phi = phi i32 [ %.pre, %bb1 ], [ %add.1, %bb ]
+; CHECK-NEXT: store i32 %add.2.pre-phi, i32* @H, align 4
+; CHECK-NEXT: ret i32 0
+    %add.2 = add nuw nsw i32 %v, 42
+    store i32 %add.2, i32* @H, align 4
+    ret i32 0
+}