Fix bug where Conditional wasn't being marked as ConstAPI

Author: Keno

base/compiler/optimize.jl

@@ -402,7 +402,8 @@ function finish(interp::AbstractInterpreter, opt::OptimizationState,
     force_noinline = _any(@nospecialize(x) -> isexpr(x, :meta) && x.args[1] === :noinline, ir.meta)
 
     # compute inlining and other related optimizations
-    if (isa(result, Const) || isconstType(result))
+    wresult = isa(result, InterConditional) ? widenconditional(result) : result
+    if (isa(wresult, Const) || isconstType(wresult))
         proven_pure = false
         # must be proven pure to use constant calling convention;
         # otherwise we might skip throwing errors (issue #20704)
@@ -436,14 +437,14 @@ function finish(interp::AbstractInterpreter, opt::OptimizationState,
             # Still set pure flag to make sure `inference` tests pass
             # and to possibly enable more optimization in the future
             src.pure = true
-            if isa(result, Const)
-                val = result.val
+            if isa(wresult, Const)
+                val = wresult.val
                 if is_inlineable_constant(val)
                     analyzed = ConstAPI(val)
                 end
             else
-                @assert isconstType(result)
-                analyzed = ConstAPI(result.parameters[1])
+                @assert isconstType(wresult)
+                analyzed = ConstAPI(wresult.parameters[1])
             end
             force_noinline || (src.inlineable = true)
         end

test/compiler/inline.jl

@@ -884,3 +884,10 @@ end
 # have_fma elimination inside ^
 f_pow() = ^(2.0, -1.0)
 @test fully_eliminated(f_pow, Tuple{})
+
+# bug where Conditional wasn't being properly marked as ConstAPI
+let
+    @noinline fcond(a, b) = a === b
+    ftest(a) = (fcond(a, nothing); a)
+    @test fully_eliminated(ftest, Tuple{Bool})
+end

test/compiler/irpasses.jl

@@ -758,3 +758,18 @@ let # effect-freeness computation for array allocation
         nothing
     end
 end
+
+# allow branch folding to look at type information
+let ci = code_typed1(optimize=false) do
+        cond = 1 + 1 == 2
+        if !cond
+            gcd(24, 36)
+        else
+            gcd(64, 128)
+        end
+    end
+    ir = Core.Compiler.inflate_ir(ci)
+    @test count(@nospecialize(stmt)->isa(stmt, Core.GotoIfNot), ir.stmts.inst) == 1
+    ir = Core.Compiler.compact!(ir, true)
+    @test count(@nospecialize(stmt)->isa(stmt, Core.GotoIfNot), ir.stmts.inst) == 0
+end