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Simplify X * C1 == C2 with undefined overflow

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this transformation is quite straightforward, without overflow, 3*X==15 is
the same as X==5 and 3*X==5 cannot happen. Adding a single_use restriction
for the first case didn't seem necessary, although of course it can
slightly increase register pressure in some cases.

2020-08-04  Marc Glisse  <marc.glisse@inria.fr>

	PR tree-optimization/95433
	* match.pd (X * C1 == C2): New transformation.

	* gcc.c-torture/execute/pr23135.c: Add -fwrapv to avoid
	undefined behavior.
	* gcc.dg/tree-ssa/pr95433.c: New file.
This commit is contained in:
Marc Glisse 2020-08-04 17:30:16 +02:00
parent c79d8335fd
commit ca2b8c082c
3 changed files with 23 additions and 1 deletions
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14
gcc/match.pd
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@ -3779,6 +3779,20 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
(scmp @0 @2)
(cmp @0 @2))))))
/* For integral types with undefined overflow fold
x * C1 == C2 into x == C2 / C1 or false. */
(for cmp (eq ne)
(simplify
(cmp (mult @0 INTEGER_CST@1) INTEGER_CST@2)
(if (INTEGRAL_TYPE_P (TREE_TYPE (@0))
&& TYPE_OVERFLOW_UNDEFINED (TREE_TYPE (@0))
&& wi::to_wide (@1) != 0)
(with { widest_int quot; }
(if (wi::multiple_of_p (wi::to_widest (@2), wi::to_widest (@1),
TYPE_SIGN (TREE_TYPE (@0)), &quot))
(cmp @0 { wide_int_to_tree (TREE_TYPE (@0), quot); })
{ constant_boolean_node (cmp == NE_EXPR, type); })))))
/* Simplify comparison of something with itself. For IEEE
floating-point, we can only do some of these simplifications. */
(for cmp (eq ge le)

2
gcc/testsuite/gcc.c-torture/execute/pr23135.c
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@ -1,7 +1,7 @@
/* Based on execute/simd-1.c, modified by joern.rennecke@st.com to
trigger a reload bug. Verified for gcc mainline from 20050722 13:00 UTC
for sh-elf -m4 -O2. */
/* { dg-options "-Wno-psabi" } */
/* { dg-options "-Wno-psabi -fwrapv" } */
/* { dg-add-options stack_size } */
#ifndef STACK_SIZE

8
gcc/testsuite/gcc.dg/tree-ssa/pr95433.c Normal file
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@ -0,0 +1,8 @@
/* { dg-do compile } */
/* { dg-options "-O -fdump-tree-optimized" } */
int f(int x){return x*7==17;}
int g(int x){return x*3==15;}
/* { dg-final { scan-tree-dump "return 0;" "optimized" } } */
/* { dg-final { scan-tree-dump "== 5;" "optimized" } } */