From 59802321785b4b9fc31b10456c62ba3a06d3a631 Mon Sep 17 00:00:00 2001
From: James Molloy <james.molloy@arm.com>
Date: Tue, 16 Aug 2016 09:45:36 +0000
Subject: [PATCH] Left shifts of negative values are defined if -fwrapv is set

This means we shouldn't emit ubsan detection code or warn.
Fixes PR25552.

llvm-svn: 278786
---
 clang/lib/CodeGen/CGExprScalar.cpp       |  3 ++-
 clang/lib/Sema/SemaExpr.cpp              |  2 +-
 clang/test/CodeGen/wrapv-lshr-sanitize.c | 12 ++++++++++++
 clang/test/Sema/negative-shift-wrapv.c   |  9 +++++++++
 4 files changed, 24 insertions(+), 2 deletions(-)
 create mode 100644 clang/test/CodeGen/wrapv-lshr-sanitize.c
 create mode 100644 clang/test/Sema/negative-shift-wrapv.c

diff --git a/clang/lib/CodeGen/CGExprScalar.cpp b/clang/lib/CodeGen/CGExprScalar.cpp
index f39368733592..700b5374ad9d 100644
--- a/clang/lib/CodeGen/CGExprScalar.cpp
+++ b/clang/lib/CodeGen/CGExprScalar.cpp
@@ -2714,7 +2714,8 @@ Value *ScalarExprEmitter::EmitShl(const BinOpInfo &Ops) {
     RHS = Builder.CreateIntCast(RHS, Ops.LHS->getType(), false, "sh_prom");
 
   bool SanitizeBase = CGF.SanOpts.has(SanitizerKind::ShiftBase) &&
-                      Ops.Ty->hasSignedIntegerRepresentation();
+                      Ops.Ty->hasSignedIntegerRepresentation() &&
+                      !CGF.getLangOpts().isSignedOverflowDefined();
   bool SanitizeExponent = CGF.SanOpts.has(SanitizerKind::ShiftExponent);
   // OpenCL 6.3j: shift values are effectively % word size of LHS.
   if (CGF.getLangOpts().OpenCL)
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 78fa995e256e..41c8a4c52a1b 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -8670,7 +8670,7 @@ static void DiagnoseBadShiftValues(Sema& S, ExprResult &LHS, ExprResult &RHS,
 
   // If LHS does not have a signed type and non-negative value
   // then, the behavior is undefined. Warn about it.
-  if (Left.isNegative()) {
+  if (Left.isNegative() && !S.getLangOpts().isSignedOverflowDefined()) {
     S.DiagRuntimeBehavior(Loc, LHS.get(),
                           S.PDiag(diag::warn_shift_lhs_negative)
                             << LHS.get()->getSourceRange());
diff --git a/clang/test/CodeGen/wrapv-lshr-sanitize.c b/clang/test/CodeGen/wrapv-lshr-sanitize.c
new file mode 100644
index 000000000000..c09dab7cf7b5
--- /dev/null
+++ b/clang/test/CodeGen/wrapv-lshr-sanitize.c
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -fsanitize=shift-base -emit-llvm %s -o - -triple x86_64-linux-gnu -fwrapv | FileCheck %s
+
+// CHECK-LABEL: @lsh_overflow
+int lsh_overflow(int a, int b) {
+  // CHECK-NOT: br
+  // CHECK-NOT: call void @__ubsan_
+  // CHECK-NOT: call void @llvm.trap
+  
+  // CHECK:      %[[RET:.*]] = shl i32
+  // CHECK-NEXT: ret i32 %[[RET]]
+  return a << b;
+}
diff --git a/clang/test/Sema/negative-shift-wrapv.c b/clang/test/Sema/negative-shift-wrapv.c
new file mode 100644
index 000000000000..b8748201ffc0
--- /dev/null
+++ b/clang/test/Sema/negative-shift-wrapv.c
@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 -Wall -ffreestanding -fsyntax-only -fwrapv -verify %s
+
+int test() {
+  int i;
+  i = -1 << 1; // no-warning
+  return i;
+}
+
+// expected-no-diagnostics