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

[Hans Wennborg via cfe-commits]

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
>>
>>
>> _______________________________________________
>> cfe-commits mailing list
>> cfe-commits at lists.llvm.org
>> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits