From 2410fb312f1e2d04c7c4abf9c2454385c5d24fa0 Mon Sep 17 00:00:00 2001
From: Shuhei Kadowaki <aviatesk@gmail.com>
Date: Sat, 2 Aug 2025 04:48:07 +0900
Subject: [PATCH] inference: propagate more `LimitedAccuracy` information more

According to Jameson's comment, we should propagate `LimitedAccuracy`
information not only when we actually use the type information of
variables that are `LimitedAccuracy`, but also when we perform
computations involving variables that are `LimitedAccuracy`. This commit
implements that propagation in relation to JuliaLang/julia#59182.
---
 Compiler/src/typelattice.jl | 28 +++++++++++++++++++---------
 1 file changed, 19 insertions(+), 9 deletions(-)

diff --git a/Compiler/src/typelattice.jl b/Compiler/src/typelattice.jl
index aae0241d69aa1..f4c3b051d3e3f 100644
--- a/Compiler/src/typelattice.jl
+++ b/Compiler/src/typelattice.jl
@@ -8,6 +8,19 @@
 # inside the global code cache.
 import Core: Const, InterConditional, PartialStruct
 
+function may_form_limited_typ(@nospecialize(aty), @nospecialize(bty), @nospecialize(xty))
+    if aty isa LimitedAccuracy
+        if bty isa LimitedAccuracy
+            return LimitedAccuracy(xty, union!(copy(aty.causes), bty.causes))
+        else
+            return LimitedAccuracy(xty, copy(aty.causes))
+        end
+    elseif bty isa LimitedAccuracy
+        return LimitedAccuracy(xty, copy(bty.causes))
+    end
+    return nothing
+end
+
 """
     cnd::Conditional
 
@@ -40,9 +53,8 @@ struct Conditional
                          isdefined::Bool=false)
         assert_nested_slotwrapper(thentype)
         assert_nested_slotwrapper(elsetype)
-        if thentype isa LimitedAccuracy || elsetype isa LimitedAccuracy
-            return Bool
-        end
+        limited = may_form_limited_typ(thentype, elsetype, Bool)
+        limited !== nothing && return limited
         return new(slot, thentype, elsetype, isdefined)
     end
 end
@@ -86,9 +98,8 @@ struct MustAlias
         assert_nested_slotwrapper(fldtyp)
         # @assert !isalreadyconst(vartyp) "vartyp is already const"
         # @assert !isalreadyconst(fldtyp) "fldtyp is already const"
-        if vartyp isa LimitedAccuracy || fldtyp isa LimitedAccuracy
-            return fldtyp
-        end
+        limited = may_form_limited_typ(vartyp, fldtyp, fldtyp)
+        limited !== nothing && return limited
         return new(slot, vartyp, fldidx, fldtyp)
     end
 end
@@ -110,9 +121,8 @@ struct InterMustAlias
         assert_nested_slotwrapper(fldtyp)
         # @assert !isalreadyconst(vartyp) "vartyp is already const"
         # @assert !isalreadyconst(fldtyp) "fldtyp is already const"
-        if vartyp isa LimitedAccuracy || fldtyp isa LimitedAccuracy
-            return fldtyp
-        end
+        limited = may_form_limited_typ(vartyp, fldtyp, fldtyp)
+        limited !== nothing && return limited
         return new(slot, vartyp, fldidx, fldtyp)
     end
 end