[gcc r17-3357] path solver: only compute ranges at the current path position [PR126876]

https://gcc.gnu.org/g:0ebadbad7c92133c467f7aed6f3c16a9e3b55774

commit r17-3357-g0ebadbad7c92133c467f7aed6f3c16a9e3b55774
Author: Aldy Hernandez <[email protected]>
Date:   Mon Aug 17 14:53:24 2026 +0000

    path solver: only compute ranges at the current path position [PR126876]
    
    Since r17-3298 the path ranger can become the current query while
    fold_using_range folds a statement, so match.pd simplifications can
    query with a context statement that can be from an arbitrary block on
    the path.  The solver's positional machinery is only meaningful at the
    block the walk is currently at.
    
    Only compute ranges at the current path position otherwise fall back
    to the global range.  Assert the positional invariant in
    range_defined_in_block, which I verified holds by testing the assert
    on a tree before r17-3298.
    
    Tested on ppc64le Linux.
    
            PR tree-optimization/126876
    
    gcc/ChangeLog:
    
            * gimple-range-path.cc
            (path_range_query::internal_range_of_expr): Only call
            range_defined_in_block at the current path position.
            (path_range_query::range_defined_in_block): Assert the current
            path position.

Diff:
---
 gcc/gimple-range-path.cc | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/gcc/gimple-range-path.cc b/gcc/gimple-range-path.cc
index 467e321b8ded..54c8a04b486f 100644
--- a/gcc/gimple-range-path.cc
+++ b/gcc/gimple-range-path.cc
@@ -156,7 +156,12 @@ path_range_query::internal_range_of_expr (vrange &r, tree name, gimple *stmt)
       return true;
     }
 
+  // We can be called from match.pd or elsewhere, with a context statement
+  // that can be anywhere on the path.  Since we can only compute ranges
+  // mid flight at the current path position, check that's the case,
+  // otherwise fall through to the global range.
   if (stmt
+      && gimple_bb (stmt) == curr_bb ()
       && range_defined_in_block (r, name, gimple_bb (stmt)))
     {
       if (TREE_CODE (name) == SSA_NAME)
@@ -290,6 +295,11 @@ path_range_query::ssa_range_in_phi (vrange &r, gphi *phi)
 bool
 path_range_query::range_defined_in_block (vrange &r, tree name, basic_block bb)
 {
+  // Ranges can only be calculated at the current path position, both
+  // while pre-computing the cache and when answering questions at the
+  // path exit afterwards.
+  gcc_assert (bb == curr_bb ());
+
   gimple *def_stmt = SSA_NAME_DEF_STMT (name);
   basic_block def_bb = gimple_bb (def_stmt);