From 1614e50d9f6d48a38e4dafb4b1a51fd4b37614f3 Mon Sep 17 00:00:00 2001
From: Evan Phoenix <evan@fallingsnow.net>
Date: Mon, 5 Oct 2009 22:53:52 +0000
Subject: [PATCH] Extend ConstantFolding to understand signed overflow variants

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@83338 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ConstantFolding.cpp          |  24 +++++
 test/Transforms/ConstProp/overflow-ops.ll | 121 +++++++++++++++++++++-
 2 files changed, 144 insertions(+), 1 deletion(-)

diff --git a/lib/Analysis/ConstantFolding.cpp b/lib/Analysis/ConstantFolding.cpp
index 1ca7cb05b41..0ce1c24bed6 100644
--- a/lib/Analysis/ConstantFolding.cpp
+++ b/lib/Analysis/ConstantFolding.cpp
@@ -678,6 +678,8 @@ llvm::canConstantFoldCallTo(const Function *F) {
   case Intrinsic::cttz:
   case Intrinsic::uadd_with_overflow:
   case Intrinsic::usub_with_overflow:
+  case Intrinsic::sadd_with_overflow:
+  case Intrinsic::ssub_with_overflow:
     return true;
   default:
     return false;
@@ -902,6 +904,28 @@ llvm::ConstantFoldCall(Function *F,
           };
           return ConstantStruct::get(F->getContext(), Ops, 2, false);
         }
+        case Intrinsic::sadd_with_overflow: {
+          Constant *Res = ConstantExpr::getAdd(Op1, Op2);           // result.
+          Constant *Overflow = ConstantExpr::getSelect(
+              ConstantExpr::getICmp(CmpInst::ICMP_SGT,
+                ConstantInt::get(Op1->getType(), 0), Op1),
+              ConstantExpr::getICmp(CmpInst::ICMP_SGT, Res, Op2), 
+              ConstantExpr::getICmp(CmpInst::ICMP_SLT, Res, Op2)); // overflow.
+
+          Constant *Ops[] = { Res, Overflow };
+          return ConstantStruct::get(F->getContext(), Ops, 2, false);
+        }
+        case Intrinsic::ssub_with_overflow: {
+          Constant *Res = ConstantExpr::getSub(Op1, Op2);           // result.
+          Constant *Overflow = ConstantExpr::getSelect(
+              ConstantExpr::getICmp(CmpInst::ICMP_SGT,
+                ConstantInt::get(Op2->getType(), 0), Op2),
+              ConstantExpr::getICmp(CmpInst::ICMP_SLT, Res, Op1), 
+              ConstantExpr::getICmp(CmpInst::ICMP_SGT, Res, Op1)); // overflow.
+
+          Constant *Ops[] = { Res, Overflow };
+          return ConstantStruct::get(F->getContext(), Ops, 2, false);
+        }
         }
       }
       
diff --git a/test/Transforms/ConstProp/overflow-ops.ll b/test/Transforms/ConstProp/overflow-ops.ll
index 52d59217b49..1547a4d0f5b 100644
--- a/test/Transforms/ConstProp/overflow-ops.ll
+++ b/test/Transforms/ConstProp/overflow-ops.ll
@@ -24,7 +24,6 @@ entry:
 ; CHECK: ret %i8i1 { i8 6, i1 true }
 }
 
-
 ;;-----------------------------
 ;; usub
 ;;-----------------------------
@@ -47,7 +46,127 @@ entry:
 ; CHECK: ret %i8i1 { i8 -2, i1 true }
 }
 
+;;-----------------------------
+;; sadd
+;;-----------------------------
+
+define {i8, i1} @sadd_1() nounwind {
+entry:
+  %t = call {i8, i1} @llvm.sadd.with.overflow.i8(i8 42, i8 2)
+  ret {i8, i1} %t
+
+; CHECK: @sadd_1
+; CHECK: ret %i8i1 { i8 44, i1 false }
+}
+
+define {i8, i1} @sadd_2() nounwind {
+entry:
+  %t = call {i8, i1} @llvm.sadd.with.overflow.i8(i8 120, i8 10)
+  ret {i8, i1} %t
+
+; CHECK: @sadd_2
+; CHECK: ret %i8i1 { i8 -126, i1 true }
+}
+
+define {i8, i1} @sadd_3() nounwind {
+entry:
+  %t = call {i8, i1} @llvm.sadd.with.overflow.i8(i8 -120, i8 10)
+  ret {i8, i1} %t
+
+; CHECK: @sadd_3
+; CHECK: ret %i8i1 { i8 -110, i1 false }
+}
+
+define {i8, i1} @sadd_4() nounwind {
+entry:
+  %t = call {i8, i1} @llvm.sadd.with.overflow.i8(i8 -120, i8 -10)
+  ret {i8, i1} %t
+
+; CHECK: @sadd_4
+; CHECK: ret %i8i1 { i8 126, i1 true }
+}
+
+define {i8, i1} @sadd_5() nounwind {
+entry:
+  %t = call {i8, i1} @llvm.sadd.with.overflow.i8(i8 2, i8 -10)
+  ret {i8, i1} %t
+
+; CHECK: @sadd_5
+; CHECK: ret %i8i1 { i8 -8, i1 false }
+}
+
+
+;;-----------------------------
+;; ssub
+;;-----------------------------
+
+define {i8, i1} @ssub_1() nounwind {
+entry:
+  %t = call {i8, i1} @llvm.ssub.with.overflow.i8(i8 4, i8 2)
+  ret {i8, i1} %t
+
+; CHECK: @ssub_1
+; CHECK: ret %i8i1 { i8 2, i1 false }
+}
+
+define {i8, i1} @ssub_2() nounwind {
+entry:
+  %t = call {i8, i1} @llvm.ssub.with.overflow.i8(i8 4, i8 6)
+  ret {i8, i1} %t
+
+; CHECK: @ssub_2
+; CHECK: ret %i8i1 { i8 -2, i1 false }
+}
+
+define {i8, i1} @ssub_3() nounwind {
+entry:
+  %t = call {i8, i1} @llvm.ssub.with.overflow.i8(i8 -10, i8 120)
+  ret {i8, i1} %t
+
+; CHECK: @ssub_3
+; CHECK: ret %i8i1 { i8 126, i1 true }
+}
+
+define {i8, i1} @ssub_3b() nounwind {
+entry:
+  %t = call {i8, i1} @llvm.ssub.with.overflow.i8(i8 -10, i8 10)
+  ret {i8, i1} %t
+
+; CHECK: @ssub_3b
+; CHECK: ret %i8i1 { i8 -20, i1 false }
+}
+
+define {i8, i1} @ssub_4() nounwind {
+entry:
+  %t = call {i8, i1} @llvm.ssub.with.overflow.i8(i8 120, i8 -10)
+  ret {i8, i1} %t
+
+; CHECK: @ssub_4
+; CHECK: ret %i8i1 { i8 -126, i1 true }
+}
+
+define {i8, i1} @ssub_4b() nounwind {
+entry:
+  %t = call {i8, i1} @llvm.ssub.with.overflow.i8(i8 20, i8 -10)
+  ret {i8, i1} %t
+
+; CHECK: @ssub_4b
+; CHECK: ret %i8i1 { i8 30, i1 false }
+}
+
+define {i8, i1} @ssub_5() nounwind {
+entry:
+  %t = call {i8, i1} @llvm.ssub.with.overflow.i8(i8 -20, i8 -10)
+  ret {i8, i1} %t
+
+; CHECK: @ssub_5
+; CHECK: ret %i8i1 { i8 -10, i1 false }
+}
+
 
 
 declare {i8, i1} @llvm.uadd.with.overflow.i8(i8, i8)
 declare {i8, i1} @llvm.usub.with.overflow.i8(i8, i8)
+
+declare {i8, i1} @llvm.sadd.with.overflow.i8(i8, i8)
+declare {i8, i1} @llvm.ssub.with.overflow.i8(i8, i8)
-- 
2.34.1