https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90078
Bug ID: 90078
Summary: ICE with deep templates caused by overflow [PATCH]
Product: gcc
Version: tree-ssa
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: wlandry at caltech dot edu
Target Milestone: ---
Created attachment 46160
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=46160&action=edit
Failing test case
Compiling the attached code with
g++ -O2 ftensorShowcase.cpp -c -ftemplate-depth=1000000
fails with the internal compiler error below. Using godbolt, it seems that
this bug started in gcc 7.1 and is still present in trunk.
In gcc/tree-ssa-loop-ivopts.c, there is a cost struct that has a concept of
infinity. For very deep, recursive templates, the cost can get larger than
'infinity' (10000000). The diff below against trunk implements saturating
arithmetic. It seems to work.
Thanks.
==============================================
diff --git a/gcc/tree-ssa-loop-ivopts.c b/gcc/tree-ssa-loop-ivopts.c
index a2b6b2b2312..a89782b13d0 100644
--- a/gcc/tree-ssa-loop-ivopts.c
+++ b/gcc/tree-ssa-loop-ivopts.c
@@ -276,7 +276,11 @@ comp_cost::operator+= (HOST_WIDE_INT c)
if (infinite_cost_p ())
return *this;
- this->cost += c;
+ /* Switch around comparison to avoid overflow */
+ if (c > infinite_cost.cost - this->cost)
+ this->cost = infinite_cost.cost;
+ else
+ this->cost += c;
return *this;
}
@@ -287,7 +291,11 @@ comp_cost::operator-= (HOST_WIDE_INT c)
if (infinite_cost_p ())
return *this;
- this->cost -= c;
+ /* Switch around comparison to avoid overflow */
+ if (c < -infinite_cost.cost + this->cost )
+ this->cost = infinite_cost.cost;
+ else
+ this->cost -= c;
return *this;
}
@@ -298,7 +306,10 @@ comp_cost::operator/= (HOST_WIDE_INT c)
if (infinite_cost_p ())
return *this;
- this->cost /= c;
+ if (c == 0)
+ this->cost = infinite_cost.cost;
+ else
+ this->cost /= c;
return *this;
}
@@ -309,7 +320,11 @@ comp_cost::operator*= (HOST_WIDE_INT c)
if (infinite_cost_p ())
return *this;
- this->cost *= c;
+ /* Switch around comparison to avoid overflow */
+ if (c > infinite_cost.cost / this->cost )
+ this->cost = infinite_cost.cost;
+ else
+ this->cost *= c;
return *this;
}
==============================================
during GIMPLE pass: ivopts
ftensorShowcase.cpp: In member function ‘auto& Tensor4_Expr<Tensor4<A, Dim0,
Dim1, Dim2, Dim3>, T, Dim0, Dim1, Dim2, Dim3, i, j, k, l>::operator=(const
Tensor4_Expr<B, U, Dim1_0, Dim1_1, Dim1_2, Dim1_3, i_1, j_1, k_1, l_1>&) [with
B = Tensor3_times_Tensor3_21<const Tensor3<float, 100, 100, 1000>, const
Tensor3<float, 1000, 100, 100>, float, float, 100, 100, 1000, 100, 100, 'l',
'm', 'k', 'n', 'o'>; U = float; int Dim1_0 = 100; int Dim1_1 = 100; int Dim1_2
= 100; int Dim1_3 = 100; char i_1 = 'l'; char j_1 = 'm'; char k_1 = 'n'; char
l_1 = 'o'; A = float; T = float; int Dim0 = 100; int Dim1 = 100; int Dim2 =
100; int Dim3 = 100; char i = 'l'; char j = 'm'; char k = 'n'; char l = 'o']’:
ftensorShowcase.cpp:170:9: internal compiler error: in try_improve_iv_set, at
tree-ssa-loop-ivopts.c:6667
auto &operator=(const Tensor4_Expr<B, U, Dim1_0, Dim1_1, Dim1_2, Dim1_3,
i_1,
^~~~~~~~
0x7f878289509a __libc_start_main
../csu/libc-start.c:308
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with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
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