implement PR4424: 0/x is always 0 for integer division.

llvm-svn: 73835

llvm/lib/VMCore/ConstantFold.cpp

@@ -773,6 +773,13 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode,
       }
       }
     }
+    
+    // 0 / x -> 0.
+    if ((Opcode == Instruction::UDiv ||
+         Opcode == Instruction::SDiv) &&
+        CI1->isZero())
+      return const_cast<Constant*>(C1);
+    
   } else if (const ConstantFP *CFP1 = dyn_cast<ConstantFP>(C1)) {
     if (const ConstantFP *CFP2 = dyn_cast<ConstantFP>(C2)) {
       APFloat C1V = CFP1->getValueAPF();

llvm/test/Transforms/ConstProp/div-zero.ll

@@ -0,0 +1,12 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep {ret i32 0}
+; PR4424
+declare void @ext()
+
+define i32 @foo(i32 %ptr) {
+entry:
+        %zero = sub i32 %ptr, %ptr              ; <i32> [#uses=1]
+        %div_zero = sdiv i32 %zero, ptrtoint (i32* getelementptr (i32* null,
+i32 1) to i32)             ; <i32> [#uses=1]
+        ret i32 %div_zero
+}
+