[PATCH] D23498: Left shifts of negative values are defined if -fwrapv is set

[James Molloy via cfe-commits]

jmolloy created this revision.
jmolloy added reviewers: davide, aaron.ballman.
jmolloy added a subscriber: cfe-commits.

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

https://reviews.llvm.org/D23498

Files:
  lib/CodeGen/CGExprScalar.cpp
  lib/Sema/SemaExpr.cpp
  test/CodeGen/wrapv-lshr-sanitize.c
  test/Sema/negative-shift-wrapv.c

Index: test/Sema/negative-shift-wrapv.c
===================================================================
--- /dev/null
+++ test/Sema/negative-shift-wrapv.c
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -Wall -ffreestanding -fsyntax-only -fwrapv -verify %s
+
+#include <limits.h>
+
+#define WORD_BIT (sizeof(int) * CHAR_BIT)
+
+void test() {
+  int i;
+  i = -1 << (WORD_BIT - 1); // no-warning
+}
+
+// expected-no-diagnostics
Index: test/CodeGen/wrapv-lshr-sanitize.c
===================================================================
--- /dev/null
+++ 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 | opt -instnamer -S | 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;
+}
Index: lib/Sema/SemaExpr.cpp
===================================================================
--- lib/Sema/SemaExpr.cpp
+++ lib/Sema/SemaExpr.cpp
@@ -8567,7 +8567,7 @@
 
   // 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());
Index: lib/CodeGen/CGExprScalar.cpp
===================================================================
--- lib/CodeGen/CGExprScalar.cpp
+++ lib/CodeGen/CGExprScalar.cpp
@@ -2706,7 +2706,8 @@
     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)


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