Peephole optims, var scoping (fixes #153) (#349)

Co-authored-by: Laurent Le Brun <laurentlb@gmail.com>

src/analyzer.fs

@@ -74,10 +74,10 @@ module private VariableInlining =
             if not ident.DoNotInline && not ident.ToBeInlined && not ident.VarDecl.Value.isEverWrittenAfterDecl then
                 match localReferences.TryGetValue(def.Key), allReferences.TryGetValue(def.Key) with
                 | (_, 1), (_, 1) when isConst ->
-                    debug $"inlining local variable '{Printer.debugIdent ident}' because it's safe to inline and used only once"
+                    debug $"inlining local variable '{Printer.debugIdent ident}' because it's safe to inline (const) and used only once"
                     ident.ToBeInlined <- true
                 | (_, 0), (_, 0) ->
-                    debug $"inlining local variable '{Printer.debugIdent ident}' because it's safe to inline and unused"
+                    debug $"inlining (removing) local variable '{Printer.debugIdent ident}' because it's safe to inline and unused"
                     ident.ToBeInlined <- true
                 | _ -> ()
 

src/rewriter.fs

@@ -11,6 +11,15 @@ let renameField field =
         field |> String.map (fun c -> options.canonicalFieldNames.[swizzleIndex c])
     else field
 
+let rec private isPure = function
+    | Var v when v.Name = "true" || v.Name = "false" -> true
+    | Int _
+    | Float _ -> true
+    | FunCall(Var fct, args) ->
+        Builtin.pureBuiltinFunctions.Contains fct.Name && List.forall isPure args
+    | FunCall(Op op, args) -> not (Builtin.assignOps.Contains op) && List.forall isPure args
+    | _ -> false
+
 module private RewriterImpl =
 
     // Remove useless spaces in macros
@@ -410,35 +419,62 @@ module private RewriterImpl =
             | Decl (_, []) -> false
             | _ -> true)
 
+        let exprUsesIdentName expr identName =
+            let mutable idents = []
+            let collectLocalUses _ = function
+                | Var v as e -> idents <- v :: idents; e
+                | e -> e
+            mapExpr (mapEnv collectLocalUses id) expr |> ignore<Expr>
+            idents |> List.exists (fun i -> i.Name = identName)
+
         // Merge two consecutive items into one, everywhere possible in a list.
-        let rec squeeze (f : 'a * 'a -> 'a option) = function
+        let rec squeeze (f : 'a * 'a -> 'a list option) = function
             | h1 :: h2 :: t ->
                 match f (h1, h2) with
-                    | Some x -> squeeze f (x :: t)
+                    | Some xs -> squeeze f (xs @ t)
                     | None -> h1 :: (squeeze f (h2 :: t))
             | h :: t -> h :: t
             | [] -> []
-
-        // Merge preceding expression into a for's init.
         let b = b |> squeeze (function
+            // Merge preceding expression into a for's init.
             | (Expr e, ForE (None, cond, inc, body)) -> // a=0;for(;i<5;++i);  ->  for(a=0;i<5;++i);
-                Some (ForE (Some e, cond, inc, body))
+                Some [ForE (Some e, cond, inc, body)]
             | (Expr e, While (cond, body)) -> // a=0;while(i<5);  ->  for(a=0;i<5;);
-                Some (ForE(Some e, Some cond, None, body))
+                Some [ForE(Some e, Some cond, None, body)]
             | Decl (_, [declElt]), Jump(JumpKeyword.Return, Some (Var v)) // int x=f();return x;  ->  return f();
                 when v.Name = declElt.name.Name && declElt.init.IsSome ->
-                    Some (Jump(JumpKeyword.Return, declElt.init))
+                    Some [Jump(JumpKeyword.Return, declElt.init)]
             | Expr (FunCall(Op "=", [Var v1; e])), Jump(JumpKeyword.Return, Some (Var v2)) // x=f();return x;  ->  return f();
                 when v1.Name = v2.Name ->
                     match v1.VarDecl with
                     | Some d ->
                         if d.scope <> VarScope.Global && not (d.ty.isOutOrInout) then
-                            Some (Jump(JumpKeyword.Return, Some e))
+                            Some [Jump(JumpKeyword.Return, Some e)]
                         else
                             None
                     | _ -> None
+            // Remove unused assignment immediately followed by re-assignment:  m=14.;m=58.;  ->  14.;m=58.;
+            | Expr (FunCall (Op "=", [Var name; init1])), (Expr (FunCall (Op "=", [Var name2; init2])) as assign2)
+                when name.Name = name2.Name && not (exprUsesIdentName init2 name.Name) ->
+                match name.Declaration with
+                | Declaration.Variable decl when decl.scope = VarScope.Global ->
+                    // The assignment should not be removed if init2 calls a function that reads the global variable.
+                    None // Safely assume it could happen.
+                | Declaration.Variable _ -> Some [Expr init1; assign2] // Transform is safe even if the var is an out parameter.
+                | _ -> None
+            // Compact a pure declaration immediately followed by re-assignment:  float m=14.;m=58.;  ->  float m=58.;
+            | Decl (ty, [declElt]), (Expr (FunCall (Op "=", [Var name2; init2])) as assign2)
+                when declElt.name.Name = name2.Name
+                    && not (exprUsesIdentName init2 declElt.name.Name)
+                    && declElt.init |> Option.map isPure |> Option.defaultValue true ->
+                Some [Decl (ty, [{declElt with init = Some init2}])]
             | _ -> None)
 
+        // Remove pure expression statements.
+        let b = b |> List.filter (function
+            | Expr e when isPure e -> false
+            | _ -> true)
+
         // Inline inner decl-less blocks. (Presence of decl could lead to redefinitions.)  a();{b();}c();  ->  a();b();c();
         let b = b |> List.collect (function
             | Block b when hasNoDecl b -> b
@@ -478,7 +514,7 @@ module private RewriterImpl =
     let simplifyStmt = function
         | Block [] as e -> e
         | Block b -> match simplifyBlock b with
-                        | [stmt] -> stmt
+                        | [stmt] as b when hasNoDecl b -> stmt
                         | stmts -> Block stmts
         | Decl (ty, li) -> Decl (rwType ty, declsNotToInline li)
         | ForD ((ty, d), cond, inc, body) -> ForD((rwType ty, declsNotToInline d), cond, inc, squeezeBlockWithComma body)
@@ -584,14 +620,7 @@ let reorderFunctions code =
 // Inline the argument of a function call into the function body.
 module private ArgumentInlining =
 
-    let rec isInlinableExpr = function
-        | Var v when v.Name = "true" || v.Name = "false" -> true
-        | Int _
-        | Float _ -> true
-        | FunCall(Var fct, args) ->
-            Builtin.pureBuiltinFunctions.Contains fct.Name && List.forall isInlinableExpr args
-        | FunCall(Op op, args) -> not (Builtin.assignOps.Contains op) && List.forall isInlinableExpr args
-        | _ -> false
+    let isInlinableExpr e = isPure e
 
     type [<NoComparison>] Inlining = {
         func: TopLevel

tests/compression_results.log

@@ -1,24 +1,24 @@
 clod.frag...                              8897 => 1528.145
 mouton/mouton.vert...                    17026 => 2457.862
 audio-flight-v2.frag                      4538 =>  891.404
-buoy.frag                                 4097 =>  624.156
-controllable-machinery.frag               7720 => 1220.140
-ed-209.frag                               7768 => 1340.423
+buoy.frag                                 4094 =>  622.550
+controllable-machinery.frag               7708 => 1220.329
+ed-209.frag                               7766 => 1341.089
 elevated.hlsl                             3405 =>  603.218
 endeavour.frag                            2605 =>  534.116
 from-the-seas-to-the-stars.frag          14292 => 2328.094
-frozen-wasteland.frag                     4583 =>  806.518
-kinder_painter.frag                       2867 =>  447.669
+frozen-wasteland.frag                     4578 =>  806.452
+kinder_painter.frag                       2865 =>  445.014
 leizex.frag                               2298 =>  510.191
 lunaquatic.frag                           5247 => 1049.030
 mandelbulb.frag                           2370 =>  538.322
 ohanami.frag                              3256 =>  722.517
 orchard.frag                              5537 => 1022.773
 oscars_chair.frag                         4651 =>  986.364
-robin.frag                                6297 => 1053.367
+robin.frag                                6295 => 1052.336
 slisesix.frag                             4573 =>  931.855
-terrarium.frag                            3626 =>  746.585
+terrarium.frag                            3624 =>  745.827
 the_real_party_is_in_your_pocket.frag    12111 => 1794.687
 valley_ball.glsl                          4386 =>  888.496
 yx_long_way_from_home.frag                2947 =>  606.406
-Total: 135097 => 23632.338
+Total: 135069 => 23627.076

tests/real/buoy.frag.expected

@@ -204,8 +204,7 @@ void mainImage(out vec4 fragColor,vec2 fragCoord)
   vec3 pos,ray;
   CamPolar(pos,ray,camRot,fragCoord);
   float to=TraceOcean(pos,ray),tb=TraceBoat(pos,ray);
-  vec3 result;
-  result=to>0.&&(to<tb||tb==0.)?
+  vec3 result=to>0.&&(to<tb||tb==0.)?
     ShadeOcean(pos+ray*to,ray,fragCoord):
     tb>0.?
       ShadeBoat(pos+ray*tb,ray):

tests/real/controllable-machinery.frag.expected

@@ -40,8 +40,7 @@ vec4 BPos(float t)
 }
 float PrBoxDf(vec3 p,vec3 b)
 {
-  vec3 d;
-  d=abs(p)-b;
+  vec3 d=abs(p)-b;
   return min(max(d.x,max(d.y,d.z)),0.)+length(max(d,0.));
 }
 float PrRoundBoxDf(vec3 p,vec3 b)
@@ -78,8 +77,7 @@ float Maxv2(vec2 p)
 }
 float SmoothMin(float a,float b,float r)
 {
-  float h;
-  h=clamp(.5+.5*(b-a)/r,0.,1.);
+  float h=clamp(.5+.5*(b-a)/r,0.,1.);
   return mix(b-h*r,a,h);
 }
 float SmoothMax(float a,float b,float r)
@@ -100,8 +98,7 @@ mat3 StdVuMat(float el,float az)
 }
 vec2 Rot2D(vec2 q,float a)
 {
-  vec2 cs;
-  cs=sin(a+vec2(1.57079635,0));
+  vec2 cs=sin(a+vec2(1.57079635,0));
   return vec2(dot(q,vec2(cs.x,-cs.y)),dot(q.yx,cs));
 }
 float GearWlDf(vec3 p,float rad,float wlThk,float tWid,float nt,float aRot,bool bev,float dMin)
@@ -241,8 +238,7 @@ float GearRay(vec3 ro,vec3 rd)
 vec3 GearNf(vec3 p)
 {
   vec4 v;
-  vec2 e;
-  e=vec2(5e-4,-5e-4);
+  vec2 e=vec2(5e-4,-5e-4);
   for(int j=VAR_ZERO;j<4;j++)
     v[j]=GearDf(p+(j<2?
       j==0?
@@ -257,8 +253,7 @@ vec3 GearNf(vec3 p)
 vec3 ObjNf(vec3 p)
 {
   vec4 v;
-  vec2 e;
-  e=vec2(5e-4,-5e-4);
+  vec2 e=vec2(5e-4,-5e-4);
   for(int j=VAR_ZERO;j<4;j++)
     v[j]=ObjDf(p+(j<2?
       j==0?
@@ -447,8 +442,7 @@ vec3 ShowScene(vec3 ro,vec3 rd)
 }
 vec4 Loadv4(int idVar)
 {
-  float fi;
-  fi=float(idVar);
+  float fi=float(idVar);
   return texture(txBuf,(vec2(mod(fi,128.),floor(fi/128.))+.5)/txSize);
 }
 void mainImage(out vec4 fragColor,vec2 fragCoord)

tests/real/ed-209.frag.expected

@@ -274,8 +274,7 @@ MarchData room(vec3 p)
   r.d=min(backWall,max(length(p.z),-doorHole+.1));
   if(r.d==backWall)
     {
-      float ocp;
-      ocp=min(abs(sdOctogon(xy,2.6)),abs(sdOctogon(xy,1.9)));
+      float ocp=min(abs(sdOctogon(xy,2.6)),abs(sdOctogon(xy,1.9)));
       ocp=max(ocp,min(.7-abs(xy.x+1.2),-xy.y));
       ocp=min(ocp,max(abs(sdOctogon(xy,1.2)),min(xy.x,.7-abs(xy.y))));
       if(ocp<.3)

tests/real/frozen-wasteland.frag.expected

@@ -234,8 +234,7 @@ vec3 Sky(vec3 rd,vec3 ligt)
 }
 float Occ(vec3 p)
 {
-  float h=0.;
-  h=clamp(map(p),.5,1.);
+  float h=clamp(map(p),.5,1.);
   return sqrt(h);
 }
 void mainImage(out vec4 fragColor,vec2 fragCoord)

tests/real/kinder_painter.expected

@@ -22,8 +22,7 @@
  "float t(vec4 z,vec3 m,vec3 v)"
  "{"
    "vec3 r=m-z.xyz;"
-   "float w=dot(v.xz,v.xz),d=dot(v.xz,r.xz),b;"
-   "b=d*d-w*(dot(r.xz,r.xz)-z.w*z.w);"
+   "float w=dot(v.xz,v.xz),d=dot(v.xz,r.xz),b=d*d-w*(dot(r.xz,r.xz)-z.w*z.w);"
    "if(b>0.)"
      "b=(-d-sqrt(b))/w;"
    "return b-.001;"

tests/real/robin.frag.expected

@@ -35,8 +35,7 @@ float noise(vec3 x)
 }
 float fbm(vec3 p)
 {
-  float f;
-  f=1.6*noise(p);
+  float f=1.6*noise(p);
   p*=2.02;
   f+=.35*noise(p);
   p*=2.33;

tests/real/terrarium.frag.expected

@@ -95,7 +95,7 @@ void main()
           else if(r<1.07)
             col=mix(col,0.,.2),p.xy=p.xy+vec2(-.5,-.866025),p=S(p);
           else
-             col=mix(col,0.,.2),col=1.,p.xy=p.xy+vec2(-.5,.866025),p=S(p),p.z+=.1;
+             mix(col,0.,.2),col=1.,p.xy=p.xy+vec2(-.5,.866025),p=S(p),p.z+=.1;
           if(time>48.)
             p.z=mix(p.z,mod(p.z+time/2.+2,4.)-2,smoothstep(48.,49.,time));
         }

tests/unit/bug321.expected

@@ -1,13 +1,13 @@
-int n;
+float n;
 float a(float s)
 {
   s=3.;
   n=2.;
   return s;
 }
-float main()
+float b()
 {
   float t=3.;
   t-=1.;
   return a(1.)+a(5.);
-}
+}

tests/unit/bug321.frag

@@ -1,12 +1,12 @@
-int n;
+float n;
 const float s = 1.;
 float a(float s)
 {
     s = 3.;
     n = 2.;
     return s;
 }
-float main()
+float b()
 {
     float t = 3.;
     t -= s;

tests/unit/conditionals.frag.expected

@@ -43,16 +43,14 @@ bool and3()
 }
 float ifStmtToExpr(float f)
 {
-  float r,r2,r3;
-  r=f>0.?
-    1.:
-    2.;
-  r2=f>1.?
-    1.:
-    (1,2.);
+  float r3;
   if(f>1.)
     r3=1.;
   else
      r3=2.,1;
-  return r+r2+r3;
+  return(f>0.?
+    1.:
+    2.)+(f>1.?
+    1.:
+    (1,2.))+r3;
 }

tests/unit/inline-aggro.aggro.expected

@@ -28,10 +28,7 @@ float inl6()
   return 2.*baz;
 }
 void notevil()
-{
-  float x=101.;
-  x=42.;
-}
+{}
 float inl7()
 {
   notevil();

tests/unit/inline-aggro.expected

@@ -29,8 +29,7 @@ float inl6()
 }
 void notevil()
 {
-  float x=101.;
-  x=42.;
+  float x=42.;
 }
 float inl7()
 {

tests/unit/inline.aggro.expected

@@ -35,8 +35,6 @@ float multiPass2()
 }
 int dont_inline_lvalue()
 {
-  int a=1;
-  a=2;
   return 3;
 }
 vec4 fragColor247;
@@ -79,3 +77,14 @@ float inline_uninitialized()
 {
   return c;
 }
+float glo;
+float noinline_readsTheGlobal()
+{
+  return glo;
+}
+float dontCompressAssigments()
+{
+  glo=10.;
+  glo=50.+noinline_readsTheGlobal();
+  return glo*glo;
+}