[gcc r11-5433] match.pd: Avoid ICE with shifts [PR97979]

[Jakub Jelinek]

https://gcc.gnu.org/g:39f5e9aded23e8b7e0e7080fc6020478b9c5b7b5

commit r11-5433-g39f5e9aded23e8b7e0e7080fc6020478b9c5b7b5
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Nov 26 10:50:23 2020 +0100

    match.pd: Avoid ICE with shifts [PR97979]
    
    My recent wide_int_binop changes caused ICE on this testcase.
    The problem is that for shift where amount has MSB set now fails to optimize
    into a constant (IMHO we should treat out of bounds shifts the same later),
    but there is a precedent for that already - e.g. division by zero fails
    to optimize into a constant too.  I think it is better if path isolation
    checks for these UBs and does something the user chooses (__builtin_trap vs.
    __builtin_unreachable, and either a deferred warning about the UB or
    nothing).
    This patch just doesn't optimize if int_const_binop failed.
    
    2020-11-26  Jakub Jelinek  <jakub@redhat.com>
    
            PR tree-optimization/97979
            * match.pd ((X {&,^,|} C2) << C1 into (X << C1) {&,^,|} (C2 << C1)):
            Only optimize if int_const_binop returned non-NULL.
    
            * gcc.dg/pr97979.c: New test.
            * gcc.c-torture/compile/pr97979.c: New test.

Diff:
---
 gcc/match.pd                                  |  3 ++-
 gcc/testsuite/gcc.c-torture/compile/pr97979.c |  7 +++++++
 gcc/testsuite/gcc.dg/pr97979.c                | 13 +++++++++++++
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/gcc/match.pd b/gcc/match.pd
index 4d290ad3c25..f8b65154a9e 100644
--- a/gcc/match.pd
+++ b/gcc/match.pd
@@ -3119,7 +3119,8 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
    (shift (convert?:s (bit_op:s @0 INTEGER_CST@2)) INTEGER_CST@1)
    (if (tree_nop_conversion_p (type, TREE_TYPE (@0)))
     (with { tree mask = int_const_binop (shift, fold_convert (type, @2), @1); }
-     (bit_op (shift (convert @0) @1) { mask; }))))))
+     (if (mask)
+      (bit_op (shift (convert @0) @1) { mask; })))))))
 
 /* ~(~X >> Y) -> X >> Y (for arithmetic shift).  */
 (simplify
diff --git a/gcc/testsuite/gcc.c-torture/compile/pr97979.c b/gcc/testsuite/gcc.c-torture/compile/pr97979.c
new file mode 100644
index 00000000000..f4f88a45adf
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/pr97979.c
@@ -0,0 +1,7 @@
+/* PR tree-optimization/97979 */
+
+int
+foo (int x)
+{
+  return (x & 0x123) << -3;
+}
diff --git a/gcc/testsuite/gcc.dg/pr97979.c b/gcc/testsuite/gcc.dg/pr97979.c
new file mode 100644
index 00000000000..44aaff2ab5a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr97979.c
@@ -0,0 +1,13 @@
+/* PR tree-optimization/97979 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fno-tree-ccp" } */
+
+short a = 0;
+int b = 0;
+
+void
+foo (void)
+{
+  unsigned short d = b;
+  a = d >> -2U;	/* { dg-warning "right shift count >= width of type" } */
+}