https://gcc.gnu.org/g:7b9d32aa2ffcb5b02643b280c8404020c1e9d6b2
commit r16-4905-g7b9d32aa2ffcb5b02643b280c8404020c1e9d6b2 Author: Andrew Pinski <[email protected]> Date: Thu Oct 30 17:46:54 2025 -0700 sccp: Fix ICE during folding after proping const in some cases [PR122497] In this case we originally had: ``` # g_4.3_21 = PHI <g_4.3_12(3)> _1 = g_4.3_21 + 2; _2 = g_2[_1][g_4.3_21]; ``` SCCP figures out g_4.3_12/g_4.3_21 is 1. final_value_replacement_loop would remove the phi defining _12. do the constant prop of the const 1 but that would ICE as we try to fold the reference `g_2[_1][g_4.3_21]` but that would try to see the range of `_1` but since `_1` refers back to _21 there would be an ICE as the phi is already been removed. The obvious fix is to move the constant prop until after the new statement for _21 is created. This fixes the change done by r14-6010-g2dde9f326ded84 and r14-6114-gde0ab339a79535. This does not fix gcc.dg/graphite/pr82819.c nor tr2/dynamic_bitset/pr92059.cc though; I will look into those issues in a few. Pushed as obvious after bootstrap/test. PR tree-optimization/122497 gcc/ChangeLog: * tree-scalar-evolution.cc (final_value_replacement_loop): Call replace_uses_by only after the replacement statement was created. gcc/testsuite/ChangeLog: * gcc.dg/torture/pr122497-1.c: New test. Signed-off-by: Andrew Pinski <[email protected]> Diff: --- gcc/testsuite/gcc.dg/torture/pr122497-1.c | 13 +++++++++++++ gcc/tree-scalar-evolution.cc | 10 +++++----- 2 files changed, 18 insertions(+), 5 deletions(-) diff --git a/gcc/testsuite/gcc.dg/torture/pr122497-1.c b/gcc/testsuite/gcc.dg/torture/pr122497-1.c new file mode 100644 index 000000000000..8b027ca3aaad --- /dev/null +++ b/gcc/testsuite/gcc.dg/torture/pr122497-1.c @@ -0,0 +1,13 @@ +/* { dg-do compile } */ +/* PR tree-optimization/122497 */ + +/* This was ICEing during SCCP + trying to simplify a reference back to the phi + which was removed. */ + +char g_2[1][2]; +int g_4, g_5; +void main() { + for (; g_4; g_4 -= 1) + g_5 = g_2[g_4 + 2][g_4]; +} diff --git a/gcc/tree-scalar-evolution.cc b/gcc/tree-scalar-evolution.cc index ecdef7529a63..7907893b916c 100644 --- a/gcc/tree-scalar-evolution.cc +++ b/gcc/tree-scalar-evolution.cc @@ -3949,11 +3949,6 @@ final_value_replacement_loop (class loop *loop) auto loc = gimple_phi_arg_location (phi, exit->dest_idx); remove_phi_node (&psi, false); - /* Propagate constants immediately, but leave an unused initialization - around to avoid invalidating the SCEV cache. */ - if (CONSTANT_CLASS_P (def) && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rslt)) - replace_uses_by (rslt, def); - /* Create the replacement statements. */ gimple_seq stmts; def = force_gimple_operand (def, &stmts, false, NULL_TREE); @@ -3961,6 +3956,11 @@ final_value_replacement_loop (class loop *loop) gimple_set_location (ass, loc); gimple_seq_add_stmt (&stmts, ass); + /* Propagate constants immediately, but leave an unused initialization + around to avoid invalidating the SCEV cache. */ + if (CONSTANT_CLASS_P (def) && !SSA_NAME_OCCURS_IN_ABNORMAL_PHI (rslt)) + replace_uses_by (rslt, def); + /* If def's type has undefined overflow and there were folded casts, rewrite all stmts added for def into arithmetics with defined overflow behavior. */
