[gcc r12-10552] rtl-optimization/54052 - RTL SSA PHI insertion compile-time hog

[Richard Biener]

https://gcc.gnu.org/g:1edc6a71feeb8460fbd4938b8926b5692fbab43f

commit r12-10552-g1edc6a71feeb8460fbd4938b8926b5692fbab43f
Author: Richard Biener <rguenther@suse.de>
Date:   Mon Feb 19 11:10:50 2024 +0100

    rtl-optimization/54052 - RTL SSA PHI insertion compile-time hog
    
    The following tries to address the PHI insertion compile-time hog in
    RTL fwprop observed with the PR54052 testcase where the loop computing
    the "unfiltered" set of variables possibly needing PHI nodes for each
    block exhibits quadratic compile-time and memory-use.
    
    It does so by pruning the local DEFs with LR_OUT of the block, removing
    regs that can never be LR_IN (defined by this block) in the dominance
    frontier.
    
            PR rtl-optimization/54052
            * rtl-ssa/blocks.cc (function_info::place_phis): Filter
            local defs by LR_OUT.
    
    (cherry picked from commit c7151283dc747769d4ac4f216d8f519bda2569b5)

Diff:
---
 gcc/rtl-ssa/blocks.cc | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/gcc/rtl-ssa/blocks.cc b/gcc/rtl-ssa/blocks.cc
index 959fad8f829d..0c5998f4b65f 100644
--- a/gcc/rtl-ssa/blocks.cc
+++ b/gcc/rtl-ssa/blocks.cc
@@ -639,7 +639,12 @@ function_info::place_phis (build_info &bi)
       if (bitmap_empty_p (&frontiers[b1]))
 	continue;
 
-      bitmap b1_def = &DF_LR_BB_INFO (BASIC_BLOCK_FOR_FN (m_fn, b1))->def;
+      // Defs in B1 that are possibly in LR_IN in the dominance frontier
+      // blocks.
+      auto_bitmap b1_def;
+      bitmap_and (b1_def, &DF_LR_BB_INFO (BASIC_BLOCK_FOR_FN (m_fn, b1))->def,
+		  DF_LR_OUT (BASIC_BLOCK_FOR_FN (m_fn, b1)));
+
       bitmap_iterator bmi;
       unsigned int b2;
       EXECUTE_IF_SET_IN_BITMAP (&frontiers[b1], 0, b2, bmi)