From fbe64f136f7650af22d90a77833eb42f8de1fbee Mon Sep 17 00:00:00 2001
From: Sanjay Patel <spatel@rotateright.com>
Date: Sun, 18 Jul 2021 13:34:43 -0400
Subject: [PATCH] [SimplifyCFG] add test to show miscompile from
 FoldBranchToCommonDest (PR51125); NFC

---
 .../SimplifyCFG/fold-branch-to-common-dest.ll      | 59 ++++++++++++++++++++--
 1 file changed, 55 insertions(+), 4 deletions(-)

diff --git a/llvm/test/Transforms/SimplifyCFG/fold-branch-to-common-dest.ll b/llvm/test/Transforms/SimplifyCFG/fold-branch-to-common-dest.ll
index 5f4226e..5ce7d60 100644
--- a/llvm/test/Transforms/SimplifyCFG/fold-branch-to-common-dest.ll
+++ b/llvm/test/Transforms/SimplifyCFG/fold-branch-to-common-dest.ll
@@ -121,10 +121,19 @@ final_right:
 ; FIXME: When we fold the dispatch block into pred, the call is moved to pred
 ; and the attribute nonnull is no longer valid on paramater. We should drop it.
 define void @one_pred_with_spec_call(i8 %v0, i8 %v1, i32* %p) {
-; CHECK-LABEL: one_pred_with_spec_call
-; CHECK-LABEL: pred:
-; CHECK:         %c0 = icmp ne i32* %p, null
-; CHECK:         %x = call i32 @speculate_call(i32* nonnull %p)
+; CHECK-LABEL: @one_pred_with_spec_call(
+; CHECK-NEXT:  pred:
+; CHECK-NEXT:    [[C0:%.*]] = icmp ne i32* [[P:%.*]], null
+; CHECK-NEXT:    [[X:%.*]] = call i32 @speculate_call(i32* nonnull [[P]])
+; CHECK-NEXT:    [[C1:%.*]] = icmp eq i8 [[V1:%.*]], 0
+; CHECK-NEXT:    [[OR_COND:%.*]] = select i1 [[C0]], i1 [[C1]], i1 false
+; CHECK-NEXT:    br i1 [[OR_COND]], label [[COMMON_RET:%.*]], label [[FINAL_RIGHT:%.*]]
+; CHECK:       common.ret:
+; CHECK-NEXT:    ret void
+; CHECK:       final_right:
+; CHECK-NEXT:    call void @sideeffect0()
+; CHECK-NEXT:    br label [[COMMON_RET]]
+;
 pred:
   %c0 = icmp ne i32* %p, null
   br i1 %c0, label %dispatch, label %final_right
@@ -988,4 +997,46 @@ for.end:
   ret void
 }
 
+; FIXME:
+; This is a miscompile if we replace a phi incoming value
+; with an updated loaded value *after* it was stored.
+
+@global_pr51125 = global i32 1, align 4
+
+define i32 @pr51125() {
+; CHECK-LABEL: @pr51125(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[LD_OLD:%.*]] = load i32, i32* @global_pr51125, align 4
+; CHECK-NEXT:    [[ISZERO_OLD:%.*]] = icmp eq i32 [[LD_OLD]], 0
+; CHECK-NEXT:    br i1 [[ISZERO_OLD]], label [[EXIT:%.*]], label [[L2:%.*]]
+; CHECK:       L2:
+; CHECK-NEXT:    [[LD_MERGE:%.*]] = phi i32 [ [[LD:%.*]], [[L2]] ], [ [[LD_OLD]], [[ENTRY:%.*]] ]
+; CHECK-NEXT:    store i32 -1, i32* @global_pr51125, align 4
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i32 [[LD_MERGE]], -1
+; CHECK-NEXT:    [[LD]] = load i32, i32* @global_pr51125, align 4
+; CHECK-NEXT:    [[ISZERO:%.*]] = icmp eq i32 [[LD]], 0
+; CHECK-NEXT:    [[OR_COND:%.*]] = select i1 [[CMP]], i1 true, i1 [[ISZERO]]
+; CHECK-NEXT:    br i1 [[OR_COND]], label [[EXIT]], label [[L2]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[R:%.*]] = phi i32 [ [[LD]], [[L2]] ], [ [[LD_OLD]], [[ENTRY]] ]
+; CHECK-NEXT:    ret i32 [[R]]
+;
+entry:
+  br label %L
+
+L:
+  %ld = load i32, i32* @global_pr51125, align 4
+  %iszero = icmp eq i32 %ld, 0
+  br i1 %iszero, label %exit, label %L2
+
+L2:
+  store i32 -1, i32* @global_pr51125, align 4
+  %cmp = icmp eq i32 %ld, -1
+  br i1 %cmp, label %L, label %exit
+
+exit:
+  %r = phi i32 [ %ld, %L2 ], [ %ld, %L ]
+  ret i32 %r
+}
+
 attributes #0 = { nounwind argmemonly speculatable }
-- 
2.7.4