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

[James Molloy via cfe-commits]

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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