The following fixes the oldest bug in my list of assigned PRs, namely
combining A / CST / CST' to A / (CST * CST'). extract_muldiv does
this in fold-const.c (but it fails to optimize to zero when CST * CST'
overflows).
Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.
Richard.
2014-12-01 Richard Biener <rguent...@suse.de>
PR tree-optimization/15346
* Makefile.in (gimple-match.o-warn): Remove -Wno-unused-parameter,
add -Wno-unused-but-set-variable.
* match.pd: Combine two successive divisions.
* gcc.dg/tree-ssa/forwprop-32.c: New testcase.
Index: gcc/match.pd
===================================================================
--- gcc/match.pd (revision 218140)
+++ gcc/match.pd (working copy)
@@ -129,6 +129,19 @@ (define_operator_list inverted_tcc_compa
&& TYPE_UNSIGNED (type))
(trunc_div @0 @1)))
+/* Combine two successive divisions. */
+(for div (trunc_div ceil_div floor_div round_div exact_div)
+ (simplify
+ (div (div @0 INTEGER_CST@1) INTEGER_CST@2)
+ (with {
+ bool overflow_p;
+ wide_int mul = wi::mul (@1, @2, TYPE_SIGN (type), &overflow_p);
+ }
+ (if (!overflow_p)
+ (div @0 { wide_int_to_tree (type, mul); }))
+ (if (overflow_p)
+ { build_zero_cst (type); }))))
+
/* Optimize A / A to 1.0 if we don't care about
NaNs or Infinities. */
(simplify
Index: gcc/testsuite/gcc.dg/tree-ssa/forwprop-32.c
===================================================================
--- gcc/testsuite/gcc.dg/tree-ssa/forwprop-32.c (revision 0)
+++ gcc/testsuite/gcc.dg/tree-ssa/forwprop-32.c (working copy)
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-forwprop1 -fdump-tree-ccp1" } */
+
+int foo (int x)
+{
+ int tem = x / 3;
+ return tem / 5;
+}
+int bar (int x)
+{
+ int tem = x / 3;
+ return tem / (__INT_MAX__ / 2);
+}
+
+/* { dg-final { scan-tree-dump "x_.\\(D\\) / 15" "forwprop1" } } */
+/* { dg-final { scan-tree-dump "return 0;" "ccp1" } } */
+/* { dg-final { cleanup-tree-dump "forwprop1" } } */
+/* { dg-final { cleanup-tree-dump "ccp1" } } */
Index: gcc/Makefile.in
===================================================================
--- gcc/Makefile.in (revision 218142)
+++ gcc/Makefile.in (working copy)
@@ -209,8 +209,8 @@ gengtype-lex.o-warn = -Wno-error
libgcov-util.o-warn = -Wno-error
libgcov-driver-tool.o-warn = -Wno-error
libgcov-merge-tool.o-warn = -Wno-error
-gimple-match.o-warn = -Wno-unused-variable -Wno-unused-parameter
-generic-match.o-warn = -Wno-unused-variable -Wno-unused-parameter
+gimple-match.o-warn = -Wno-unused-variable -Wno-unused-but-set-variable
+generic-match.o-warn = -Wno-unused-variable -Wno-unused-but-set-variable
# All warnings have to be shut off in stage1 if the compiler used then
# isn't gcc; configure determines that. WARN_CFLAGS will be either
