Simplify X * C1 == C2 with undefined overflow

[Marc Glisse]

Hello,

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.

Bootstrap+regtest on x86_64-pc-linux-gnu.

2020-08-03  Marc Glisse  <marc.gli...@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.

--
Marc Glissediff --git a/gcc/match.pd b/gcc/match.pd
index a052c9e3dbc..78fd8cf5d9e 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -1578,6 +1578,20 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
 	&& wi::neg_p (wi::to_wide (@1), TYPE_SIGN (TREE_TYPE (@1))))
     (cmp @2 @0))))))
 
+/* 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); })
+     { build_int_cst (type, cmp == NE_EXPR); })))))
+
 /* (X - 1U) <= INT_MAX-1U into (int) X > 0.  */
 (for cmp (le gt)
      icmp (gt le)
diff --git a/gcc/testsuite/gcc.c-torture/execute/pr23135.c b/gcc/testsuite/gcc.c-torture/execute/pr23135.c
index e740ff52874..ef9b7efc9c4 100644
--- a/gcc/testsuite/gcc.c-torture/execute/pr23135.c
+++ b/gcc/testsuite/gcc.c-torture/execute/pr23135.c
@@ -1,7 +1,7 @@
 /* Based on execute/simd-1.c, modified by joern.renne...@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
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr95433.c b/gcc/testsuite/gcc.dg/tree-ssa/pr95433.c
new file mode 100644
index 00000000000..4e161ee26cc
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr95433.c
@@ -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" } } */