In this PR we tried to create a widening multiply of two 3-bit numbers,
but that isn't a widening multiply at the optab/rtl level, since both
the input and output still have the same mode.
We could trap this either in is_widening_mult_p or (as the patch does)
in the routines that actually ask for an optab. The latter seemed
more natural since is_widening_mult_p doesn't otherwise care about modes.
Tested on aarch64-linux-gnu, x86_64-linux-gnu and powerpc64-linux-gnu.
OK to install?
Richard
2017-11-03 Richard Sandiford <richard.sandif...@linaro.org>
Alan Hayward <alan.hayw...@arm.com>
David Sherwood <david.sherw...@arm.com>
gcc/
PR tree-optimization/82816
* tree-ssa-math-opts.c (convert_mult_to_widen): Return false
if the modes of the two types are the same.
(convert_plusminus_to_widen): Likewise.
gcc/testsuite/
* gcc.c-torture/compile/pr82816.c: New test.
Index: gcc/tree-ssa-math-opts.c
===================================================================
--- gcc/tree-ssa-math-opts.c 2017-11-01 12:29:40.203534002 +0000
+++ gcc/tree-ssa-math-opts.c 2017-11-03 11:18:03.046411241 +0000
@@ -3259,6 +3259,9 @@ convert_mult_to_widen (gimple *stmt, gim
to_mode = SCALAR_INT_TYPE_MODE (type);
from_mode = SCALAR_INT_TYPE_MODE (type1);
+ if (to_mode == from_mode)
+ return false;
+
from_unsigned1 = TYPE_UNSIGNED (type1);
from_unsigned2 = TYPE_UNSIGNED (type2);
@@ -3449,6 +3452,9 @@ convert_plusminus_to_widen (gimple_stmt_
to_mode = SCALAR_TYPE_MODE (type);
from_mode = SCALAR_TYPE_MODE (type1);
+ if (to_mode == from_mode)
+ return false;
+
from_unsigned1 = TYPE_UNSIGNED (type1);
from_unsigned2 = TYPE_UNSIGNED (type2);
optype = type1;
Index: gcc/testsuite/gcc.c-torture/compile/pr82816.c
===================================================================
--- /dev/null 2017-11-03 10:40:07.002381728 +0000
+++ gcc/testsuite/gcc.c-torture/compile/pr82816.c 2017-11-03
11:18:03.045411265 +0000
@@ -0,0 +1,12 @@
+struct A
+{
+ int b:3;
+} d, e;
+
+int c;
+
+void f ()
+{
+ char g = d.b * e.b;
+ c = g;
+}
