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author | Iain Buclaw <ibuclaw@gdcproject.org> | 2023-06-26 03:24:27 +0200 |
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committer | Iain Buclaw <ibuclaw@gdcproject.org> | 2023-06-26 03:26:22 +0200 |
commit | ab98db1e8c1b997414539f41b7fb814019497d8d (patch) | |
tree | 8d9ff30f938173dc164d56a95ae7dd27a356d7ea /gcc | |
parent | f445b42e1881fe875c61ad8f7aa080121dd89ab3 (diff) | |
download | gcc-ab98db1e8c1b997414539f41b7fb814019497d8d.zip gcc-ab98db1e8c1b997414539f41b7fb814019497d8d.tar.gz gcc-ab98db1e8c1b997414539f41b7fb814019497d8d.tar.bz2 |
d: Suboptimal codegen for __builtin_expect(cond, false)
Since PR96435, both boolean objects and expressions have been evaluated
in the following way.
(*(ubyte*)&obj_or_expr) & 1
It has been noted that sometimes this can cause the back-end to optimize
in non-obvious ways - in particular with __builtin_expect.
This @safe feature is now restricted to just when reading the value of a
bool field that comes from a union.
PR d/110359
gcc/d/ChangeLog:
* d-convert.cc (convert_for_rvalue): Only apply the @safe boolean
conversion to boolean fields of a union.
(convert_for_condition): Call convert_for_rvalue in the default case.
gcc/testsuite/ChangeLog:
* gdc.dg/pr110359.d: New test.
Diffstat (limited to 'gcc')
-rw-r--r-- | gcc/d/d-convert.cc | 31 | ||||
-rw-r--r-- | gcc/testsuite/gdc.dg/pr110359.d | 22 |
2 files changed, 41 insertions, 12 deletions
diff --git a/gcc/d/d-convert.cc b/gcc/d/d-convert.cc index cdbd69c..2b9d8e7 100644 --- a/gcc/d/d-convert.cc +++ b/gcc/d/d-convert.cc @@ -619,7 +619,7 @@ convert_expr (tree exp, Type *etype, Type *totype) return result ? result : convert (build_ctype (totype), exp); } -/* Return a TREE represenwation of EXPR, whose type has been converted from +/* Return a TREE representation of EXPR, whose type has been converted from * ETYPE to TOTYPE, and is being used in an rvalue context. */ tree @@ -634,20 +634,27 @@ convert_for_rvalue (tree expr, Type *etype, Type *totype) { /* If casting from bool, the result is either 0 or 1, any other value violates @safe code, so enforce that it is never invalid. */ - if (CONSTANT_CLASS_P (expr)) - result = d_truthvalue_conversion (expr); - else + for (tree ref = expr; TREE_CODE (ref) == COMPONENT_REF; + ref = TREE_OPERAND (ref, 0)) { - /* Reinterpret the boolean as an integer and test the first bit. - The generated code should end up being equivalent to: + /* If the expression is a field that's part of a union, reinterpret + the boolean as an integer and test the first bit. The generated + code should end up being equivalent to: *cast(ubyte *)&expr & 1; */ - machine_mode bool_mode = TYPE_MODE (TREE_TYPE (expr)); - tree mtype = lang_hooks.types.type_for_mode (bool_mode, 1); - result = fold_build2 (BIT_AND_EXPR, mtype, - build_vconvert (mtype, expr), - build_one_cst (mtype)); + if (TREE_CODE (TREE_TYPE (TREE_OPERAND (ref, 0))) == UNION_TYPE) + { + machine_mode bool_mode = TYPE_MODE (TREE_TYPE (expr)); + tree mtype = lang_hooks.types.type_for_mode (bool_mode, 1); + result = fold_build2 (BIT_AND_EXPR, mtype, + build_vconvert (mtype, expr), + build_one_cst (mtype)); + break; + } } + if (result == NULL_TREE) + result = d_truthvalue_conversion (expr); + result = convert (build_ctype (tbtype), result); } @@ -844,7 +851,7 @@ convert_for_condition (tree expr, Type *type) break; default: - result = expr; + result = convert_for_rvalue (expr, type, type); break; } diff --git a/gcc/testsuite/gdc.dg/pr110359.d b/gcc/testsuite/gdc.dg/pr110359.d new file mode 100644 index 0000000..bf69201 --- /dev/null +++ b/gcc/testsuite/gdc.dg/pr110359.d @@ -0,0 +1,22 @@ +// https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110359 +// { dg-do compile } +// { dg-options "-fdump-tree-original" } +double pow(in double x, in ulong p) +{ + import gcc.builtins : __builtin_expect; + if (__builtin_expect(p == 0, false)) + return 1; + if (__builtin_expect(p == 1, false)) + return x; + + double s = x; + double v = 1; + for (ulong i = p; i > 1; i >>= 1) + { + v = (i & 0x1) ? s * v : v; + s = s * s; + } + return v * s; +} +// { dg-final { scan-tree-dump "if \\(__builtin_expect \\(p == 0, 0\\) != 0\\)" "original" } } +// { dg-final { scan-tree-dump "if \\(__builtin_expect \\(p == 1, 0\\) != 0\\)" "original" } } |