From a547b4e26b311e417cd51100e379693f51a3f448 Mon Sep 17 00:00:00 2001
From: Petr Hosek <phosek@google.com>
Date: Tue, 6 Apr 2021 22:30:28 -0700
Subject: [PATCH] Revert "[InstCombine] Fold `((X - Y) - Z)` to `X - (Y + Z)`
 (PR49858)"

This reverts commit 31d219d2997fed1b7dc97e0adf170d5aaf65883e which
causes an infinite loop when compiling the XRay runtime.
---
 llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp |  6 ------
 llvm/test/Transforms/InstCombine/abs-1.ll             |  4 ++--
 llvm/test/Transforms/InstCombine/sub-from-sub.ll      | 12 ++++++------
 3 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 4ced599..bacb868 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1801,12 +1801,6 @@ Instruction *InstCombinerImpl::visitSub(BinaryOperator &I) {
     return BinaryOperator::CreateSub(XZ, YW);
   }
 
-  // ((X - Y) - Op1)  -->  X - (Y + Op1)
-  if (match(Op0, m_OneUse(m_Sub(m_Value(X), m_Value(Y))))) {
-    Value *Add = Builder.CreateAdd(Y, Op1);
-    return BinaryOperator::CreateSub(X, Add);
-  }
-
   auto m_AddRdx = [](Value *&Vec) {
     return m_OneUse(m_Intrinsic<Intrinsic::vector_reduce_add>(m_Value(Vec)));
   };
diff --git a/llvm/test/Transforms/InstCombine/abs-1.ll b/llvm/test/Transforms/InstCombine/abs-1.ll
index ea77dfb..7452798 100644
--- a/llvm/test/Transforms/InstCombine/abs-1.ll
+++ b/llvm/test/Transforms/InstCombine/abs-1.ll
@@ -305,9 +305,9 @@ define i32 @nabs_canonical_8(i32 %a) {
 define i32 @nabs_canonical_9(i32 %a, i32 %b) {
 ; CHECK-LABEL: @nabs_canonical_9(
 ; CHECK-NEXT:    [[T1:%.*]] = sub i32 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT:    [[T2:%.*]] = sub i32 [[B]], [[A]]
 ; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.abs.i32(i32 [[T1]], i1 false)
-; CHECK-NEXT:    [[TMP2:%.*]] = add i32 [[TMP1]], [[A]]
-; CHECK-NEXT:    [[ADD:%.*]] = sub i32 [[B]], [[TMP2]]
+; CHECK-NEXT:    [[ADD:%.*]] = sub i32 [[T2]], [[TMP1]]
 ; CHECK-NEXT:    ret i32 [[ADD]]
 ;
   %t1 = sub i32 %a, %b
diff --git a/llvm/test/Transforms/InstCombine/sub-from-sub.ll b/llvm/test/Transforms/InstCombine/sub-from-sub.ll
index aaa8b1d..202dbd1 100644
--- a/llvm/test/Transforms/InstCombine/sub-from-sub.ll
+++ b/llvm/test/Transforms/InstCombine/sub-from-sub.ll
@@ -8,8 +8,8 @@ declare void @use8(i8)
 ; Basic test
 define i8 @t0(i8 %x, i8 %y, i8 %z) {
 ; CHECK-LABEL: @t0(
-; CHECK-NEXT:    [[TMP1:%.*]] = add i8 [[Y:%.*]], [[Z:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = sub i8 [[X:%.*]], [[TMP1]]
+; CHECK-NEXT:    [[I0:%.*]] = sub i8 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = sub i8 [[I0]], [[Z:%.*]]
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %i0 = sub i8 %x, %y
@@ -20,8 +20,8 @@ define i8 @t0(i8 %x, i8 %y, i8 %z) {
 ; No flags are propagated
 define i8 @t1_flags(i8 %x, i8 %y, i8 %z) {
 ; CHECK-LABEL: @t1_flags(
-; CHECK-NEXT:    [[TMP1:%.*]] = add i8 [[Y:%.*]], [[Z:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = sub i8 [[X:%.*]], [[TMP1]]
+; CHECK-NEXT:    [[O0:%.*]] = sub nuw nsw i8 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = sub nuw nsw i8 [[O0]], [[Z:%.*]]
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %o0 = sub nuw nsw i8 %x, %y
@@ -47,8 +47,8 @@ define i8 @n2(i8 %x, i8 %y, i8 %z) {
 
 define i8 @t3_c0(i8 %y, i8 %z) {
 ; CHECK-LABEL: @t3_c0(
-; CHECK-NEXT:    [[TMP1:%.*]] = add i8 [[Y:%.*]], [[Z:%.*]]
-; CHECK-NEXT:    [[R:%.*]] = sub i8 42, [[TMP1]]
+; CHECK-NEXT:    [[I0:%.*]] = sub i8 42, [[Y:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = sub i8 [[I0]], [[Z:%.*]]
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %i0 = sub i8 42, %y
-- 
2.7.4