In the CBackend, use casts to force integer add, subtract, and

multiply to be done as unsigned, so that they have well defined
behavior on overflow. This fixes PR2408.

llvm-svn: 53767

3 files changed, 42 insertions, 1 deletions

diff --git a/llvm/lib/Target/CBackend/CBackend.cpp b/llvm/lib/Target/CBackend/CBackend.cpp
index 71895f4cbbd..34511e8a3a8 100644
--- a/llvm/lib/Target/CBackend/CBackend.cpp
+++ b/llvm/lib/Target/CBackend/CBackend.cpp
@@ -1116,6 +1116,13 @@ bool CWriter::printConstExprCast(const ConstantExpr* CE) {
   const Type *Ty = CE->getOperand(0)->getType();
   bool TypeIsSigned = false;
   switch (CE->getOpcode()) {
+  case Instruction::Add:
+  case Instruction::Sub:
+  case Instruction::Mul:
+    // We need to cast integer arithmetic so that it is always performed
+    // as unsigned, to avoid undefined behavior on overflow.
+    if (!Ty->isIntOrIntVector()) break;
+    // FALL THROUGH
   case Instruction::LShr:
   case Instruction::URem: 
   case Instruction::UDiv: NeedsExplicitCast = true; break;
@@ -1174,6 +1181,13 @@ void CWriter::printConstantWithCast(Constant* CPV, unsigned Opcode) {
     default:
       // for most instructions, it doesn't matter
       break; 
+    case Instruction::Add:
+    case Instruction::Sub:
+    case Instruction::Mul:
+      // We need to cast integer arithmetic so that it is always performed
+      // as unsigned, to avoid undefined behavior on overflow.
+      if (!OpTy->isIntOrIntVector()) break;
+      // FALL THROUGH
     case Instruction::LShr:
     case Instruction::UDiv:
     case Instruction::URem:
@@ -1294,6 +1308,13 @@ void CWriter::writeOperand(Value *Operand) {
 bool CWriter::writeInstructionCast(const Instruction &I) {
   const Type *Ty = I.getOperand(0)->getType();
   switch (I.getOpcode()) {
+  case Instruction::Add:
+  case Instruction::Sub:
+  case Instruction::Mul:
+    // We need to cast integer arithmetic so that it is always performed
+    // as unsigned, to avoid undefined behavior on overflow.
+    if (!Ty->isIntOrIntVector()) break;
+    // FALL THROUGH
   case Instruction::LShr:
   case Instruction::URem: 
   case Instruction::UDiv: 
@@ -1334,6 +1355,13 @@ void CWriter::writeOperandWithCast(Value* Operand, unsigned Opcode) {
     default:
       // for most instructions, it doesn't matter
       break; 
+    case Instruction::Add:
+    case Instruction::Sub:
+    case Instruction::Mul:
+      // We need to cast integer arithmetic so that it is always performed
+      // as unsigned, to avoid undefined behavior on overflow.
+      if (!OpTy->isIntOrIntVector()) break;
+      // FALL THROUGH
     case Instruction::LShr:
     case Instruction::UDiv:
     case Instruction::URem: // Cast to unsigned first
diff --git a/llvm/test/CodeGen/CBackend/2007-02-23-NameConflicts.ll b/llvm/test/CodeGen/CBackend/2007-02-23-NameConflicts.ll
index 2bc4d516808..eb5cb864465 100644
--- a/llvm/test/CodeGen/CBackend/2007-02-23-NameConflicts.ll
+++ b/llvm/test/CodeGen/CBackend/2007-02-23-NameConflicts.ll
@@ -1,7 +1,8 @@
 ; PR1164
 ; RUN: llvm-as < %s | llc -march=c | grep {llvm_cbe_A = \\*llvm_cbe_G;}
 ; RUN: llvm-as < %s | llc -march=c | grep {llvm_cbe_B = \\*(&ltmp_0_1);}
-; RUN: llvm-as < %s | llc -march=c | grep {return (llvm_cbe_A + llvm_cbe_B);}
+; RUN: llvm-as < %s | llc -march=c | grep {return (((unsigned int )(((unsigned int )llvm_cbe_A) + ((unsigned int )llvm_cbe_B))));}
+
 @G = global i32 123
 @ltmp_0_1 = global i32 123
 
diff --git a/llvm/test/CodeGen/CBackend/pr2408.ll b/llvm/test/CodeGen/CBackend/pr2408.ll
new file mode 100644
index 00000000000..a16f91bfad8
--- /dev/null
+++ b/llvm/test/CodeGen/CBackend/pr2408.ll
@@ -0,0 +1,12 @@
+; RUN: llvm-as < %s | llc -march=c | grep {\\* ((unsigned int )}
+; PR2408
+
+define i32 @a(i32 %a) {
+entry:
+        %shr = ashr i32 %a, 0           ; <i32> [#uses=1]
+        %shr2 = ashr i32 2, 0           ; <i32> [#uses=1]
+        %mul = mul i32 %shr, %shr2              ; <i32> [#uses=1]
+        %shr4 = ashr i32 2, 0           ; <i32> [#uses=1]
+        %div = sdiv i32 %mul, %shr4             ; <i32> [#uses=1]
+        ret i32 %div
+}