[llvm-branch-commits] [llvm] release/22.x: [SystemZ] Limit depth of findCCUse() (#185922) (PR #186052)

[via llvm-branch-commits]

https://github.com/llvmbot created https://github.com/llvm/llvm-project/pull/186052

Backport 11e0d6ae4b00114d642f03168f57a007464bf5f6

Requested by: @nikic

>From 8e18855761a69bba7ba2ead63f54c8e464240ce9 Mon Sep 17 00:00:00 2001
From: Nikita Popov <npopov at redhat.com>
Date: Thu, 12 Mar 2026 09:00:38 +0100
Subject: [PATCH] [SystemZ] Limit depth of findCCUse() (#185922)

The recursion here has potentially exponential complexity. Avoid this by
limiting the depth of recursion.

An alternative would be to memoize the results. I went with the simpler
depth limit on the assumption that we don't particularly care about very
deep value chains here.

Fixes https://github.com/llvm/llvm-project/issues/185905.

(cherry picked from commit 11e0d6ae4b00114d642f03168f57a007464bf5f6)
---
 llvm/lib/Target/SystemZ/SystemZISelLowering.cpp | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
index 21beef238f187..8f21e00983601 100644
--- a/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
+++ b/llvm/lib/Target/SystemZ/SystemZISelLowering.cpp
@@ -8705,7 +8705,12 @@ SDValue SystemZTargetLowering::combineSETCC(
   return SDValue();
 }
 
-static std::pair<SDValue, int> findCCUse(const SDValue &Val) {
+static std::pair<SDValue, int> findCCUse(const SDValue &Val,
+                                         unsigned Depth = 0) {
+  // Limit depth of potentially exponential walk.
+  if (Depth > 5)
+    return std::make_pair(SDValue(), SystemZ::CCMASK_NONE);
+
   switch (Val.getOpcode()) {
   default:
     return std::make_pair(SDValue(), SystemZ::CCMASK_NONE);
@@ -8718,7 +8723,7 @@ static std::pair<SDValue, int> findCCUse(const SDValue &Val) {
     SDValue Op4CCReg = Val.getOperand(4);
     if (Op4CCReg.getOpcode() == SystemZISD::ICMP ||
         Op4CCReg.getOpcode() == SystemZISD::TM) {
-      auto [OpCC, OpCCValid] = findCCUse(Op4CCReg.getOperand(0));
+      auto [OpCC, OpCCValid] = findCCUse(Op4CCReg.getOperand(0), Depth + 1);
       if (OpCC != SDValue())
         return std::make_pair(OpCC, OpCCValid);
     }
@@ -8735,10 +8740,10 @@ static std::pair<SDValue, int> findCCUse(const SDValue &Val) {
   case ISD::SHL:
   case ISD::SRA:
   case ISD::SRL:
-    auto [Op0CC, Op0CCValid] = findCCUse(Val.getOperand(0));
+    auto [Op0CC, Op0CCValid] = findCCUse(Val.getOperand(0), Depth + 1);
     if (Op0CC != SDValue())
       return std::make_pair(Op0CC, Op0CCValid);
-    return findCCUse(Val.getOperand(1));
+    return findCCUse(Val.getOperand(1), Depth + 1);
   }
 }