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__builtin_constant_p used to be short-cut evaluated to false when
building with -O0. This is undesirable as it means that constant folding
in the front-end can give different results than folding in the back-end.
It can also create conditional branches on constant conditions that don't
get folded away. With the pending improvements to the llvm.is.constant
handling on the LLVM side, the short-cut is no longer useful.
Adjust various codegen tests to not depend on the short-cut or the
backend optimisations.
Differential Revision: https://reviews.llvm.org/D67638
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@374742 91177308-0d34-0410-b5e6-96231b3b80d8
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us emitting the operand of __builtin_constant_p if it has side-effects.
Original commit message:
Fix interactions between __builtin_constant_p and constexpr to match
current trunk GCC.
GCC permits information from outside the operand of
__builtin_constant_p (but in the same constant evaluation context) to be
used within that operand; clang now does so too. A few other minor
deviations from GCC's behavior showed up in my testing and are also
fixed (matching GCC):
* Clang now supports nullptr_t as the argument type for
__builtin_constant_p
* Clang now returns true from __builtin_constant_p if called with a
null pointer
* Clang now returns true from __builtin_constant_p if called with an
integer cast to pointer type
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@359367 91177308-0d34-0410-b5e6-96231b3b80d8
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Summary:
Some ASM input constraints (e.g., "i" and "n") require immediate values. At O0,
very few code transformations are performed. So if we cannot resolve to an
immediate when emitting the ASM input we shouldn't delay its processing.
Reviewers: rsmith, efriedma
Reviewed By: efriedma
Subscribers: rehana, efriedma, craig.topper, jyknight, cfe-commits
Differential Revision: https://reviews.llvm.org/D55616
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@349561 91177308-0d34-0410-b5e6-96231b3b80d8
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The constant emitter may need to evaluate the expression in a constant context.
For exasmple, global initializer lists.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@348070 91177308-0d34-0410-b5e6-96231b3b80d8
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Kept the "indirect_builtin_constant_p" test case in test/SemaCXX/constant-expression-cxx1y.cpp
while we are investigating why the following snippet fails:
extern char extern_var;
struct { int a; } a = {__builtin_constant_p(extern_var)};
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@348039 91177308-0d34-0410-b5e6-96231b3b80d8
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git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@348032 91177308-0d34-0410-b5e6-96231b3b80d8
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git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@348029 91177308-0d34-0410-b5e6-96231b3b80d8
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This was reverted in r347656 due to me thinking it caused a miscompile of
Chromium. Turns out it was the Chromium code that was broken.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@347756 91177308-0d34-0410-b5e6-96231b3b80d8
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This caused a miscompile in Chrome (see crbug.com/908372) that's
illustrated by this small reduction:
static bool f(int *a, int *b) {
return !__builtin_constant_p(b - a) || (!(b - a));
}
int arr[] = {1,2,3};
bool g() {
return f(arr, arr + 3);
}
$ clang -O2 -S -emit-llvm a.cc -o -
g() should return true, but after r347417 it became false for some reason.
This also reverts the follow-up commits.
r347417:
> Re-Reinstate 347294 with a fix for the failures.
>
> Don't try to emit a scalar expression for a non-scalar argument to
> __builtin_constant_p().
>
> Third time's a charm!
r347446:
> The result of is.constant() is unsigned.
r347480:
> A __builtin_constant_p() returns 0 with a function type.
r347512:
> isEvaluatable() implies a constant context.
>
> Assume that we're in a constant context if we're asking if the expression can
> be compiled into a constant initializer. This fixes the issue where a
> __builtin_constant_p() in a compound literal was diagnosed as not being
> constant, even though it's always possible to convert the builtin into a
> constant.
r347531:
> A "constexpr" is evaluated in a constant context. Make sure this is reflected
> if a __builtin_constant_p() is a part of a constexpr.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@347656 91177308-0d34-0410-b5e6-96231b3b80d8
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Assume that we're in a constant context if we're asking if the expression can
be compiled into a constant initializer. This fixes the issue where a
__builtin_constant_p() in a compound literal was diagnosed as not being
constant, even though it's always possible to convert the builtin into a
constant.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@347512 91177308-0d34-0410-b5e6-96231b3b80d8
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git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@347480 91177308-0d34-0410-b5e6-96231b3b80d8
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git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@347446 91177308-0d34-0410-b5e6-96231b3b80d8
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