Nomination for 3.9: r278786 - Left shifts of negative values are defined if -fwrapv is set

[Aaron Ballman via cfe-commits]

I'm not Richard, but I agree with merging it into 3.9 nonetheless. :-)

~Aaron

On Tue, Aug 16, 2016 at 12:30 PM, Hans Wennborg via cfe-commits
<cfe-commits at lists.llvm.org> wrote:
> Seems reasonable to me if Richard agrees.
>
> On Tue, Aug 16, 2016 at 3:01 AM, James Molloy <james at jamesmolloy.co.uk> wrote:
>> Hi Hans,
>>
>> [cc. Richard as code owner]
>>
>> I'd like to nominate this commit for 3.9. The actual code churn is tiny, and
>> this fixes a problem noticed by and causing pain to the qemu project.
>>
>> Cheers,
>>
>> James
>>
>> On Tue, 16 Aug 2016 at 10:53 James Molloy via cfe-commits
>> <cfe-commits at lists.llvm.org> wrote:
>>>
>>> Author: jamesm
>>> Date: Tue Aug 16 04:45:36 2016
>>> New Revision: 278786
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=278786&view=rev
>>> Log:
>>> Left shifts of negative values are defined if -fwrapv is set
>>>
>>> This means we shouldn't emit ubsan detection code or warn.
>>> Fixes PR25552.
>>>
>>> Added:
>>>     cfe/trunk/test/CodeGen/wrapv-lshr-sanitize.c
>>>     cfe/trunk/test/Sema/negative-shift-wrapv.c
>>> Modified:
>>>     cfe/trunk/lib/CodeGen/CGExprScalar.cpp
>>>     cfe/trunk/lib/Sema/SemaExpr.cpp
>>>
>>> Modified: cfe/trunk/lib/CodeGen/CGExprScalar.cpp
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGExprScalar.cpp?rev=278786&r1=278785&r2=278786&view=diff
>>>
>>> ==============================================================================
>>> --- cfe/trunk/lib/CodeGen/CGExprScalar.cpp (original)
>>> +++ cfe/trunk/lib/CodeGen/CGExprScalar.cpp Tue Aug 16 04:45:36 2016
>>> @@ -2714,7 +2714,8 @@ Value *ScalarExprEmitter::EmitShl(const
>>>      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)
>>>
>>> Modified: cfe/trunk/lib/Sema/SemaExpr.cpp
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaExpr.cpp?rev=278786&r1=278785&r2=278786&view=diff
>>>
>>> ==============================================================================
>>> --- cfe/trunk/lib/Sema/SemaExpr.cpp (original)
>>> +++ cfe/trunk/lib/Sema/SemaExpr.cpp Tue Aug 16 04:45:36 2016
>>> @@ -8670,7 +8670,7 @@ static void DiagnoseBadShiftValues(Sema&
>>>
>>>    // 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());
>>>
>>> Added: cfe/trunk/test/CodeGen/wrapv-lshr-sanitize.c
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/wrapv-lshr-sanitize.c?rev=278786&view=auto
>>>
>>> ==============================================================================
>>> --- cfe/trunk/test/CodeGen/wrapv-lshr-sanitize.c (added)
>>> +++ cfe/trunk/test/CodeGen/wrapv-lshr-sanitize.c Tue Aug 16 04:45:36 2016
>>> @@ -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;
>>> +}
>>>
>>> Added: cfe/trunk/test/Sema/negative-shift-wrapv.c
>>> URL:
>>> http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/negative-shift-wrapv.c?rev=278786&view=auto
>>>
>>> ==============================================================================
>>> --- cfe/trunk/test/Sema/negative-shift-wrapv.c (added)
>>> +++ cfe/trunk/test/Sema/negative-shift-wrapv.c Tue Aug 16 04:45:36 2016
>>> @@ -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
>>>
>>>
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