From c23f29d6f05b1fe4fa2dd50cbb78ee2b30e0de4d Mon Sep 17 00:00:00 2001
From: Vitaly Buka <vitalybuka@google.com>
Date: Sat, 18 Feb 2023 12:21:10 -0800
Subject: [PATCH] Revert "[SimplifyCFG] Check if the return instruction causes
 undefined behavior"

Breaks bots
https://lab.llvm.org/buildbot/#/builders/236/builds/2349
https://lab.llvm.org/buildbot/#/builders/74/builds/17361
https://lab.llvm.org/buildbot/#/builders/168/builds/11972

This reverts commit 7be55b007698f6b6398cbbea69c327b5a971938a.
---
 llvm/lib/Transforms/Utils/SimplifyCFG.cpp          | 14 ----
 .../SimplifyCFG/unreachable-eliminate-on-ret.ll    | 86 ----------------------
 2 files changed, 100 deletions(-)
 delete mode 100644 llvm/test/Transforms/SimplifyCFG/unreachable-eliminate-on-ret.ll

diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index f6d3022..372a669 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -7126,20 +7126,6 @@ static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I, bool PtrValu
         return passingValueIsAlwaysUndefined(V, GEP, PtrValueMayBeModified);
       }
 
-    // Look through return.
-    if (ReturnInst *Ret = dyn_cast<ReturnInst>(Use)) {
-      bool HasNoUndefAttr =
-          Ret->getFunction()->hasRetAttribute(Attribute::NoUndef);
-      // Return undefined to a noundef return value is undefined.
-      if (isa<UndefValue>(C) && HasNoUndefAttr)
-        return true;
-      // Return null to a nonnull+noundef return value is undefined.
-      if (C->isNullValue() && HasNoUndefAttr &&
-          Ret->getFunction()->hasRetAttribute(Attribute::NonNull)) {
-        return true;
-      }
-    }
-
     // Look through bitcasts.
     if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
       return passingValueIsAlwaysUndefined(V, BC, PtrValueMayBeModified);
diff --git a/llvm/test/Transforms/SimplifyCFG/unreachable-eliminate-on-ret.ll b/llvm/test/Transforms/SimplifyCFG/unreachable-eliminate-on-ret.ll
deleted file mode 100644
index cb3e066..0000000
--- a/llvm/test/Transforms/SimplifyCFG/unreachable-eliminate-on-ret.ll
+++ /dev/null
@@ -1,86 +0,0 @@
-; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt -passes=simplifycfg -simplifycfg-require-and-preserve-domtree=1 -S < %s | FileCheck %s
-
-define noundef i32 @test_ret_noundef(i1 %cond) {
-; CHECK-LABEL: @test_ret_noundef(
-; CHECK-NEXT:  entry:
-; CHECK-NEXT:    ret i32 1
-;
-entry:
-  br i1 %cond, label %bb1, label %bb2
-
-bb1:
-  br label %bb2
-
-bb2:
-  %r = phi i32 [ undef, %entry ], [ 1, %bb1 ]
-  ret i32 %r
-}
-
-define i32 @test_ret(i1 %cond) {
-; CHECK-LABEL: @test_ret(
-; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[COND:%.*]], i32 1, i32 undef
-; CHECK-NEXT:    ret i32 [[SPEC_SELECT]]
-;
-entry:
-  br i1 %cond, label %bb1, label %bb2
-
-bb1:
-  br label %bb2
-
-bb2:
-  %r = phi i32 [ undef, %entry ], [ 1, %bb1 ]
-  ret i32 %r
-}
-
-define nonnull noundef ptr @test_ret_nonnull_noundef(i1 %cond, ptr %x) {
-; CHECK-LABEL: @test_ret_nonnull_noundef(
-; CHECK-NEXT:  entry:
-; CHECK-NEXT:    call void @llvm.assume(i1 [[COND:%.*]])
-; CHECK-NEXT:    ret ptr [[X:%.*]]
-;
-entry:
-  br i1 %cond, label %bb1, label %bb2
-
-bb1:
-  br label %bb2
-
-bb2:
-  %r = phi ptr [ null, %entry ], [ %x, %bb1 ]
-  ret ptr %r
-}
-
-define nonnull ptr @test_ret_nonnull(i1 %cond, ptr %x) {
-; CHECK-LABEL: @test_ret_nonnull(
-; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[COND:%.*]], ptr [[X:%.*]], ptr null
-; CHECK-NEXT:    ret ptr [[SPEC_SELECT]]
-;
-entry:
-  br i1 %cond, label %bb1, label %bb2
-
-bb1:
-  br label %bb2
-
-bb2:
-  %r = phi ptr [ null, %entry ], [ %x, %bb1 ]
-  ret ptr %r
-}
-
-define ptr @test_ret_ptr(i1 %cond, ptr %x) {
-; CHECK-LABEL: @test_ret_ptr(
-; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[COND:%.*]], ptr [[X:%.*]], ptr null
-; CHECK-NEXT:    ret ptr [[SPEC_SELECT]]
-;
-entry:
-  br i1 %cond, label %bb1, label %bb2
-
-bb1:
-  br label %bb2
-
-bb2:
-  %r = phi ptr [ null, %entry ], [ %x, %bb1 ]
-  ret ptr %r
-}
-- 
2.7.4