From e0e960923ff3666c090cd4e4a3509377f1ecf167 Mon Sep 17 00:00:00 2001
From: Vitaly Buka <vitalybuka@google.com>
Date: Mon, 15 Aug 2022 14:59:50 -0700
Subject: [PATCH] [AArch64] Fix signed integer overflow in CSINC case

Followup to D131815, which overlflows on different
values.
---
 llvm/lib/Target/AArch64/AArch64ISelLowering.cpp | 20 ++++++++++---------
 llvm/test/CodeGen/AArch64/arm64-csel.ll         | 26 +++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 9 deletions(-)

diff --git a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
index 92e6430..4481138 100644
--- a/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
+++ b/llvm/lib/Target/AArch64/AArch64ISelLowering.cpp
@@ -8235,15 +8235,17 @@ SDValue AArch64TargetLowering::LowerSELECT_CC(ISD::CondCode CC, SDValue LHS,
             Swap = true;
           }
         }
-        // 64-bit check whether we can use CSINC. To avoid signed integer
-        // overflow the condition ignores wrap around, which is already
-        // handled by CSINV above.
-      } else if (1 ==
-                 std::max(TrueVal, FalseVal) - std::min(TrueVal, FalseVal)) {
-        Opcode = AArch64ISD::CSINC;
-
-        if (TrueVal > FalseVal) {
-          Swap = true;
+      } else {
+        // 64-bit check whether we can use CSINC.
+        const uint64_t TrueVal64 = TrueVal;
+        const uint64_t FalseVal64 = FalseVal;
+
+        if ((TrueVal64 == FalseVal64 + 1) || (TrueVal64 + 1 == FalseVal64)) {
+          Opcode = AArch64ISD::CSINC;
+
+          if (TrueVal > FalseVal) {
+            Swap = true;
+          }
         }
       }
 
diff --git a/llvm/test/CodeGen/AArch64/arm64-csel.ll b/llvm/test/CodeGen/AArch64/arm64-csel.ll
index cbb367d..e04b42d 100644
--- a/llvm/test/CodeGen/AArch64/arm64-csel.ll
+++ b/llvm/test/CodeGen/AArch64/arm64-csel.ll
@@ -292,6 +292,32 @@ entry:
   ret i64 %.
 }
 
+; Regression test for FalseVal - TrueVal overflow
+define i64 @foo18_overflow3(i1 %cmp) nounwind readnone optsize ssp {
+; CHECK-LABEL: foo18_overflow3:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    mov x8, #-9223372036854775808 
+; CHECK-NEXT:    tst w0, #0x1 
+; CHECK-NEXT:    csel x0, x8, xzr, ne 
+; CHECK-NEXT:    ret
+entry:
+  %. = select i1 %cmp, i64 -9223372036854775808, i64 0
+  ret i64 %.
+}
+
+; Regression test for TrueVal - FalseVal overflow
+define i64 @foo18_overflow4(i1 %cmp) nounwind readnone optsize ssp {
+; CHECK-LABEL: foo18_overflow4:
+; CHECK:       // %bb.0: // %entry
+; CHECK-NEXT:    mov x8, #-9223372036854775808 
+; CHECK-NEXT:    tst w0, #0x1 
+; CHECK-NEXT:    csel x0, xzr, x8, ne 
+; CHECK-NEXT:    ret
+entry:
+  %. = select i1 %cmp, i64 0, i64 -9223372036854775808
+  ret i64 %.
+}
+
 define i64 @foo19(i64 %a, i64 %b, i64 %c) {
 ; CHECK-LABEL: foo19:
 ; CHECK:       // %bb.0: // %entry
-- 
2.7.4