PR9350: increment/decrement of char (and anything else narrower than int)

can't overflow due to promotion rules; emit a wrapping add for those cases.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@126816 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/CGExprScalar.cpp b/lib/CodeGen/CGExprScalar.cpp
index c4ff8df38153a5e10ae9bf7a1f13d31092de9afe..b11236a97f8e0b9be8712a021cae91b1161fc5fb 100644 (file)
--- a/lib/CodeGen/CGExprScalar.cpp
+++ b/lib/CodeGen/CGExprScalar.cpp
@@ -1278,10 +1278,12 @@ ScalarExprEmitter::EmitScalarPrePostIncDec(const UnaryOperator *E, LValue LV,
 
     llvm::Value *amt = llvm::ConstantInt::get(value->getType(), amount);
 
-    if (type->isSignedIntegerType())
+    // Note that signed integer inc/dec with width less than int can't
+    // overflow because of promotion rules; we're just eliding a few steps here.
+    if (type->isSignedIntegerType() &&
+        value->getType()->getPrimitiveSizeInBits() >=
+            CGF.CGM.IntTy->getBitWidth())
       value = EmitAddConsiderOverflowBehavior(E, value, amt, isInc);
-
-    // Unsigned integer inc is always two's complement.
     else
       value = Builder.CreateAdd(value, amt, isInc ? "inc" : "dec");
   

diff --git a/test/CodeGen/integer-overflow.c b/test/CodeGen/integer-overflow.c
index 066ef895744e3f47a0f429bd1192e45937f8d347..1d460656a1c7acd468bad62c80b540974f5c4477 100644 (file)
--- a/test/CodeGen/integer-overflow.c
+++ b/test/CodeGen/integer-overflow.c
@@ -50,11 +50,17 @@ void test1() {
   // TRAPV_HANDLER: foo(
   --a;
   
-  
   // -fwrapv should turn off inbounds for GEP's, PR9256
   extern int* P;
   ++P;
   // DEFAULT: getelementptr inbounds i32*
   // WRAPV: getelementptr i32*
   // TRAPV: getelementptr inbounds i32*
+
+  // PR9350: char increment never overflows.
+  extern volatile signed char PR9350;
+  // DEFAULT: add i8 {{.*}}, 1
+  // WRAPV: add i8 {{.*}}, 1
+  // TRAPV: add i8 {{.*}}, 1
+  ++PR9350;
 }