From 31b00b4c72f89cf7e9e61733141838cf7819f2db Mon Sep 17 00:00:00 2001
From: KrystalDelusion <93062060+KrystalDelusion@users.noreply.github.com>
Date: Fri, 31 Jan 2025 11:03:33 +1300
Subject: [PATCH 1/2] celledges: Use b_width_capped for left shifts

`b_width_capped` already exists for preventing arithmetic overflow, limiting the value of `b_width` to 30.  This just changes the left shifts to also use it.
The caveat of incorrect results for extremely large values of `a_width` still applies, as does the improbability of that actually happening.
This fixes #4844 (or at least, the floating point exception; the circuit still isn't valid but I think that's fine).
---
 kernel/celledges.cc | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/celledges.cc b/kernel/celledges.cc
index bad7124d9b1..68e55db02c7 100644
--- a/kernel/celledges.cc
+++ b/kernel/celledges.cc
@@ -253,13 +253,13 @@ void shift_op(AbstractCellEdgesDatabase *db, RTLIL::Cell *cell)
 				if (a_width == 1 && is_signed) {
 					int skip = 1 << (k + 1);
 					int base = skip -1;
-					if (i % skip != base && i - a_width + 2 < 1 << b_width)
+					if (i % skip != base && i - a_width + 2 < 1 << b_width_capped)
 						db->add_edge(cell, ID::B, k, ID::Y, i, -1);	
 				} else if (is_signed) {
-					if (i - a_width + 2 < 1 << b_width)
+					if (i - a_width + 2 < 1 << b_width_capped)
 						db->add_edge(cell, ID::B, k, ID::Y, i, -1);
 				} else {
-					if (i - a_width + 1 < 1 << b_width)
+					if (i - a_width + 1 < 1 << b_width_capped)
 						db->add_edge(cell, ID::B, k, ID::Y, i, -1);
 				}
 			// right shifts

From cf52cf300916d82eaee0194b29d9ae342c0a6d68 Mon Sep 17 00:00:00 2001
From: KrystalDelusion <93062060+KrystalDelusion@users.noreply.github.com>
Date: Fri, 31 Jan 2025 12:15:53 +1300
Subject: [PATCH 2/2] nowrshmsk: Check for stride==0

log2(0) returns -inf, which gives undefined behaviour when casting to an int.  So catch the case when it's 0 just set the width to 0.
---
 frontends/ast/simplify.cc | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/frontends/ast/simplify.cc b/frontends/ast/simplify.cc
index b00cde28e2c..d35756d4ed3 100644
--- a/frontends/ast/simplify.cc
+++ b/frontends/ast/simplify.cc
@@ -2936,7 +2936,10 @@ bool AstNode::simplify(bool const_fold, int stage, int width_hint, bool sign_hin
 					lsb_expr->children[stride_ix]->detectSignWidth(stride_width, stride_sign);
 					max_width = std::max(i_width, stride_width);
 					// Stride width calculated from actual stride value.
-					stride_width = std::ceil(std::log2(std::abs(stride)));
+					if (stride == 0)
+						stride_width = 0;
+					else
+						stride_width = std::ceil(std::log2(std::abs(stride)));
 
 					if (i_width + stride_width > max_width) {
 						// For (truncated) i*stride to be within the range of dst, the following must hold: