From 8045c7393bc83060f812d0f7b1221edbc767407c Mon Sep 17 00:00:00 2001
From: Ryan Flynn <pizza@parseerror.com>
Date: Sat, 8 Aug 2009 19:18:23 +0000
Subject: [PATCH] PR4700 - remove shift by 0 warning

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@78488 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/clang/Basic/DiagnosticSemaKinds.td |  3 ---
 lib/Sema/SemaExpr.cpp                      | 11 +----------
 test/Sema/shift.c                          | 11 ++++++++---
 3 files changed, 9 insertions(+), 16 deletions(-)

diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index 591cf0a28a..fb36a717f4 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1241,9 +1241,6 @@ def warn_shift_negative : Warning<
   "shift count is negative">;
 def warn_shift_gt_typewidth : Warning<
   "shift count >= width of type">;
-def warn_op_no_effect : Warning<
-  "operation has no effect">,
-  InGroup<DiagGroup<"all">>, DefaultIgnore;
 
 def err_sizeof_nonfragile_interface : Error<
   "invalid application of '%select{alignof|sizeof}1' to interface %0 in "
diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index cec1aeafac..f00ab5412d 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -4136,16 +4136,7 @@ QualType Sema::CheckShiftOperands(Expr *&lex, Expr *&rex, SourceLocation Loc,
   llvm::APSInt Right;
   // Check right/shifter operand
   if (rex->isIntegerConstantExpr(Right, Context)) {
-    // Check left/shiftee operand
-    llvm::APSInt Left;
-    if (lex->isIntegerConstantExpr(Left, Context)) {
-      if (Left == 0 && Right != 0)
-        Diag(Loc, diag::warn_op_no_effect)
-          << lex->getSourceRange() << rex->getSourceRange();
-    }
-    if (isCompAssign && Right == 0)
-      Diag(Loc, diag::warn_op_no_effect) << rex->getSourceRange();
-    else if (Right.isNegative())
+    if (Right.isNegative())
       Diag(Loc, diag::warn_shift_negative) << rex->getSourceRange();
     else {
       llvm::APInt LeftBits(Right.getBitWidth(),
diff --git a/test/Sema/shift.c b/test/Sema/shift.c
index 4c2b88a7f0..2516d1b861 100644
--- a/test/Sema/shift.c
+++ b/test/Sema/shift.c
@@ -12,15 +12,15 @@ void test() {
   char c;
 
   c = 0 << 0;
-  c = 0 << 1; // expected-warning {{no effect}}
+  c = 0 << 1;
   c = 1 << 0;
   c = 1 << -0;
   c = 1 >> -0;
   c = 1 << -1; // expected-warning {{shift count is negative}}
   c = 1 >> -1; // expected-warning {{shift count is negative}}
   c = 1 << c;
-  c <<= 0; // expected-warning {{no effect}}
-  c >>= 0; // expected-warning {{no effect}}
+  c <<= 0;
+  c >>= 0;
   c <<= 1;
   c >>= 1;
   c <<= -1; // expected-warning {{shift count is negative}}
@@ -33,3 +33,8 @@ void test() {
   c >>= CHAR_BIT+1; // expected-warning {{shift count >= width of type}}
   (void)((long)c << CHAR_BIT);
 }
+
+#define a 0
+#define ashift 8
+enum { b = (a << ashift) };
+
-- 
2.40.0