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* [gcc r13-5152] c++: Avoid some false positive -Wfloat-conversion warnings with extended precision [PR108285]
@ 2023-01-13 17:24 Jakub Jelinek
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From: Jakub Jelinek @ 2023-01-13 17:24 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:3456db4de8940235b303ca38a689353854c9239f
commit r13-5152-g3456db4de8940235b303ca38a689353854c9239f
Author: Jakub Jelinek <jakub@redhat.com>
Date: Fri Jan 13 18:23:57 2023 +0100
c++: Avoid some false positive -Wfloat-conversion warnings with extended precision [PR108285]
On the following testcase trunk emits a false positive warning on ia32.
convert_like_internal is there called with type of double and
expr EXCESS_PRECISION_EXPR with float type with long double operand
2.L * (long double) x.
Now, for the code generation we do the right thing, cp_convert
to double from that 2.L * (long double) x, but we call even
cp_convert_and_check with that and that emits the -Wfloat-conversion
warning. Looking at what the C FE does in this case, it calls
convert_and_check with the EXCESS_PRECISION_EXPR expression rather
than its operand, and essentially uses the operand for code generation
and EXCESS_PRECISION_EXPR itself for warnings.
The following patch does that too for the C++ FE.
2023-01-13 Jakub Jelinek <jakub@redhat.com>
PR c++/108285
* cvt.cc (cp_convert_and_check): For EXCESS_PRECISION_EXPR
use its operand except that for warning purposes use the original
EXCESS_PRECISION_EXPR.
* call.cc (convert_like_internal): Only look through
EXCESS_PRECISION_EXPR when calling cp_convert, not when calling
cp_convert_and_check.
* g++.dg/warn/pr108285.C: New test.
Diff:
---
gcc/cp/call.cc | 8 +++++---
gcc/cp/cvt.cc | 6 ++++--
gcc/testsuite/g++.dg/warn/pr108285.C | 11 +++++++++++
3 files changed, 20 insertions(+), 5 deletions(-)
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index bd174b8d655..2cad1c059d8 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -8863,12 +8863,14 @@ convert_like_internal (conversion *convs, tree expr, tree fn, int argnum,
return error_mark_node;
warning_sentinel w (warn_zero_as_null_pointer_constant);
- if (TREE_CODE (expr) == EXCESS_PRECISION_EXPR)
- expr = TREE_OPERAND (expr, 0);
if (issue_conversion_warnings)
expr = cp_convert_and_check (totype, expr, complain);
else
- expr = cp_convert (totype, expr, complain);
+ {
+ if (TREE_CODE (expr) == EXCESS_PRECISION_EXPR)
+ expr = TREE_OPERAND (expr, 0);
+ expr = cp_convert (totype, expr, complain);
+ }
return expr;
}
diff --git a/gcc/cp/cvt.cc b/gcc/cp/cvt.cc
index 434d306961f..1cd2b4ad9e1 100644
--- a/gcc/cp/cvt.cc
+++ b/gcc/cp/cvt.cc
@@ -652,8 +652,10 @@ cp_convert (tree type, tree expr, tsubst_flags_t complain)
tree
cp_convert_and_check (tree type, tree expr, tsubst_flags_t complain)
{
- tree result;
+ tree result, expr_for_warning = expr;
+ if (TREE_CODE (expr) == EXCESS_PRECISION_EXPR)
+ expr = TREE_OPERAND (expr, 0);
if (TREE_TYPE (expr) == type)
return expr;
if (expr == error_mark_node)
@@ -663,7 +665,7 @@ cp_convert_and_check (tree type, tree expr, tsubst_flags_t complain)
if ((complain & tf_warning)
&& c_inhibit_evaluation_warnings == 0)
{
- tree folded = cp_fully_fold (expr);
+ tree folded = cp_fully_fold (expr_for_warning);
tree folded_result;
if (folded == expr)
folded_result = result;
diff --git a/gcc/testsuite/g++.dg/warn/pr108285.C b/gcc/testsuite/g++.dg/warn/pr108285.C
new file mode 100644
index 00000000000..74cb234a7ca
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/pr108285.C
@@ -0,0 +1,11 @@
+// PR c++/108285
+// { dg-do compile }
+// { dg-options "-fexcess-precision=standard -Wfloat-conversion" }
+
+void bar (double);
+
+void
+foo (float x)
+{
+ bar (2 * x); // { dg-bogus "conversion from '\[^\n\r]\*' to 'double' may change value" }
+}
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