From 8ab6cf1ca887986800af9bf2ea612d9d40af05f7 Mon Sep 17 00:00:00 2001
From: ringabout <43030857+ringabout@users.noreply.github.com>
Date: Fri, 22 Sep 2023 01:47:29 +0800
Subject: [PATCH] fixes #22246; generate __builtin_unreachable hints for case
 defaults (#22737)

fixes #22246
resurrects #22350

(cherry picked from commit a1b6fa9420db09f2660ad5919d2b96673f324f8f)
---
 compiler/ccgstmts.nim | 7 +++++--
 compiler/extccomp.nim | 5 +++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/compiler/ccgstmts.nim b/compiler/ccgstmts.nim
index 3197389814..448a437db7 100644
--- a/compiler/ccgstmts.nim
+++ b/compiler/ccgstmts.nim
@@ -971,8 +971,11 @@ proc genOrdinalCase(p: BProc, n: PNode, d: var TLoc) =
         hasDefault = true
       exprBlock(p, branch.lastSon, d)
       lineF(p, cpsStmts, "break;$n", [])
-    if (hasAssume in CC[p.config.cCompiler].props) and not hasDefault:
-      lineF(p, cpsStmts, "default: __assume(0);$n", [])
+    if not hasDefault:
+      if hasBuiltinUnreachable in CC[p.config.cCompiler].props:
+        lineF(p, cpsStmts, "default: __builtin_unreachable();$n", [])
+      elif hasAssume in CC[p.config.cCompiler].props:
+        lineF(p, cpsStmts, "default: __assume(0);$n", [])
     lineF(p, cpsStmts, "}$n", [])
   if lend != "": fixLabel(p, lend)
 
diff --git a/compiler/extccomp.nim b/compiler/extccomp.nim
index 2429ce2785..cb9a6ba2aa 100644
--- a/compiler/extccomp.nim
+++ b/compiler/extccomp.nim
@@ -33,6 +33,7 @@ type
     hasGnuAsm,                # CC's asm uses the absurd GNU assembler syntax
     hasDeclspec,              # CC has __declspec(X)
     hasAttribute,             # CC has __attribute__((X))
+    hasBuiltinUnreachable     # CC has __builtin_unreachable
   TInfoCCProps* = set[TInfoCCProp]
   TInfoCC* = tuple[
     name: string,        # the short name of the compiler
@@ -95,7 +96,7 @@ compiler gcc:
     produceAsm: gnuAsmListing,
     cppXsupport: "-std=gnu++17 -funsigned-char",
     props: {hasSwitchRange, hasComputedGoto, hasCpp, hasGcGuard, hasGnuAsm,
-            hasAttribute})
+            hasAttribute, hasBuiltinUnreachable})
 
 # GNU C and C++ Compiler
 compiler nintendoSwitchGCC:
@@ -122,7 +123,7 @@ compiler nintendoSwitchGCC:
     produceAsm: gnuAsmListing,
     cppXsupport: "-std=gnu++17 -funsigned-char",
     props: {hasSwitchRange, hasComputedGoto, hasCpp, hasGcGuard, hasGnuAsm,
-            hasAttribute})
+            hasAttribute, hasBuiltinUnreachable})
 
 # LLVM Frontend for GCC/G++
 compiler llvmGcc: