Rewrite while into for, take opportunities to save semi-colons

README.md

@@ -463,6 +463,26 @@ Output:
 return y ? z : w;
 ```
 
+### Loops
+
+`while` loops are rewritten as `for` loops. This sometimes enable removing semi-colons or braces,
+either by moving the preceding statement into the initialization of the `for`,
+or by moving the last statement of the loop body into the increment part of the `for`.
+
+Input:
+```glsl
+i = 0.;
+while (i < 50) {
+	f(i);
+	i++;
+}
+```
+
+Output:
+```glsl
+for(i=0.;i<50;i++)f(i);
+```
+
 ### Merge declarations
 
 If multiple values of the same type are declared next to each other, we can merge

src/rewriter.fs

@@ -352,6 +352,14 @@ let squeezeBlockWithComma = function
         else stmt
     | stmt -> stmt
 
+let hasNoDecl = List.forall (function Decl _ -> false | _ -> true)
+
+let rec hasNoContinue stmts = stmts |> List.forall (function
+    | Jump (JumpKeyword.Continue, _) -> false
+    | If (_cond, bodyT, bodyF) -> hasNoContinue [bodyT] && hasNoContinue (Option.toList bodyF)
+    | Switch (_e, cases) -> cases |> List.forall (fun (_label, stmts) -> hasNoContinue stmts)
+    | _ -> true)
+
 let private simplifyBlock stmts = 
     let b = stmts
     // Avoid some optimizations when there are preprocessor directives.
@@ -368,7 +376,22 @@ let private simplifyBlock stmts =
         | Decl (_, []) -> false
         | _ -> true)
 
-    let hasNoDecl = List.forall (function Decl _ -> false | _ -> true)
+    // Merge two consecutive items into one, everywhere possible in a list.
+    let rec squeeze (f : 'a * 'a -> 'a option) = function
+        | h1 :: h2 :: t ->
+            match f (h1, h2) with
+                | Some x -> squeeze f (x :: t)
+                | None -> h1 :: (squeeze f (h2 :: t))
+        | h :: t -> h :: t
+        | [] -> []
+
+    // Merge preceding expression into a for's init.
+    let b = b |> squeeze (function
+        | (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))
+        | (Expr e, While (cond, body)) -> // a=0;while(i<5);  ->  for(a=0;i<5;);
+            Some (ForE(Some e, Some cond, None, body))
+        | _ -> None)
 
     // Inline inner decl-less blocks. (Presence of decl could lead to redefinitions.)  a();{b();}c();  ->  a();b();c();
     let b = b |> List.collect (function
@@ -414,11 +437,27 @@ let private simplifyStmt = function
     | Decl (ty, li) -> Decl (rwType ty, declsNotToInline li)
     | ForD ((ty, d), cond, inc, body) -> ForD((rwType ty, declsNotToInline d), cond, inc, squeezeBlockWithComma body)
     | ForE (init, cond, inc, body) -> ForE(init, cond, inc, squeezeBlockWithComma body)
-    | While (cond, body) -> While (cond, squeezeBlockWithComma body)
+    | While (cond, body) ->
+        match body with
+        | Expr e -> ForE (None, Some cond, Some e, Block []) // while(c)b();  ->  for(;c;b());
+        | Block stmts ->
+            match List.rev stmts with
+            | Expr last :: revBody when hasNoContinue stmts && hasNoDecl stmts ->
+                // This rewrite is only valid if:
+                // * continue is never used in this loop, and
+                // * the last expression of the body does not use any Decl from the body.
+                let block = match (List.rev revBody) with
+                            | [stmt] -> stmt
+                            | stmts -> Block stmts
+                ForE (None, Some cond, Some last, block) // while(c){a();b();}  ->  for(;c;b())a();
+            | _ -> ForE (None, Some cond, None, squeezeBlockWithComma (Block stmts))
+        | _ -> ForE (None, Some cond, None, squeezeBlockWithComma body)
     | DoWhile (cond, body) -> DoWhile (cond, squeezeBlockWithComma body)
     | If (True, e1, _) -> squeezeBlockWithComma e1
     | If (False, _, Some e2) -> squeezeBlockWithComma e2
     | If (False, _, None) -> Block []
+    | If (cond, Block [], None) -> Expr cond // if(c);  ->  c;
+    | If (cond, Block [], Some (Block [])) -> Expr cond // if(c)else{};  ->  c;
     | If (c, b, Some (Block [])) -> If(c, b, None) // "else{}"  ->  ""
     | If (cond, body1, body2) ->
         let (body1, body2) = squeezeBlockWithComma body1, Option.map squeezeBlockWithComma body2

tests/commands.txt

@@ -22,6 +22,7 @@
 --no-renaming --no-inlining --format indented -o tests/unit/vectors.frag.expected tests/unit/vectors.frag
 --no-renaming --format indented -o tests/unit/deadcode.frag.expected tests/unit/deadcode.frag
 --no-renaming --no-inlining --format indented -o tests/unit/augmented.frag.expected tests/unit/augmented.frag
+--no-remove-unused --no-renaming -o tests/unit/loop.frag.expected tests/unit/loop.frag
 
 # Inlining unit tests
 

tests/compression_results.log

@@ -1,4 +1,4 @@
-from-the-seas-to-the-stars.frag          14313 => 2358.823
+from-the-seas-to-the-stars.frag          14305 => 2358.450
 the_real_party_is_in_your_pocket.frag    12196 => 1829.311
 ed-209.frag                               7888 => 1361.583
 valley_ball.glsl                          4369 =>  890.945
@@ -14,4 +14,4 @@ elevated.hlsl                             3406 =>  611.302
 buoy.frag                                 4194 =>  622.602
 orchard.frag                              5588 => 1051.886
 robin.frag                                6293 => 1066.421
-Total: 87663 => 15860.542
+Total: 87655 => 15860.170

tests/real/from-the-seas-to-the-stars.frag.expected

@@ -432,8 +432,7 @@ void main()
                       w.y=R();
                       w.z=R();
                       w.w=R();
-                      if(w.w<.5)
-                        ;
+                      w.w<.5;
                     }
                 }
             p.xyz+=(w.xyz*2-1)*pow(length(p),2)*.001;
@@ -485,8 +484,7 @@ void main()
                     w.y=R();
                     w.z=R();
                     w.w=R();
-                    if(w.w<.5)
-                      ;
+                    w.w<.5;
                   }
               }
               p.xyz+=(w.xyz*2-1)*pow(length(p),2)*.001;

tests/real/sult.expected

@@ -18,18 +18,18 @@ const char *sult_frag =
  "float f=0.,w=10.;"
  "float e(vec3 m)"
  "{"
-   "float y=c,z,a=0.,g,o,t;"
+   "float y=c,g,z=0.,o,a,t;"
    "vec3 r;"
    "m+=(sin(m.zxy*1.7+y)+sin(m.yzx+y*3.))*.2;"
-   "a=v<6.?"
+   "z=v<6.?"
      "length(m.xyz*vec3(1,1,.1)-vec3(0,-.1,y*.15-.3))-.34:"
      "length(m.xy+vec2(0,.7))-.3+(sin(m.z*17.+y*.6)+sin(m.z*2.)*6.)*.01;"
    "m.xy=vec2(atan(m.x,m.y)*1.113,1.6-length(m.xy)-sin(y*2.)*.3);"
    "r=fract(m.xzz+.5).xyz-.5;"
    "r.y=(m.y-.35)*1.3;"
-   "z=max(abs(m.y-.3)-.05,abs(length(fract(m.xz)-.5)-.4)-.03);"
-   "f=step(a,z);"
-   "return min(min(z,a),m.y-.2);"
+   "g=max(abs(m.y-.3)-.05,abs(length(fract(m.xz)-.5)-.4)-.03);"
+   "f=step(z,g);"
+   "return min(min(g,z),m.y-.2);"
  "}"
  "vec3 d=vec3(.19,.2,.24),o=vec3(1),t=vec3(.45,.01,0),g=vec3(.17,0,0);"
  "void main()"
@@ -39,14 +39,11 @@ const char *sult_frag =
    "float C=1.,b=0.,Z,Y,X=0.,W,V,U,T;"
    "u=vec3(.01,0,0);"
    "h=u.yyy;"
-   "while(C>.1)"
-     "{"
-       "for(Z=X,Y=1.;Z<w&&Y>.005;Z+=Y)"
-         "Y=e(p+i*Z);"
-       "Z<w?"
-         "(p+=i*Z,W=e(p),U=f,F=normalize(-vec3(W-e(p+u.xyy),W-e(p+u.yxy),W-e(p+u.yyx))),V=clamp(e(p+F*.05)*4.+e(p+F*.1)*2.+.5,.1,1.),b=U*.3,F=normalize(F+step(4.,v)*f*sin(p.yzx*40.)*.05),i=reflect(i,F),T=clamp(dot(normalize(m),F),0.,1.),F=mix(mix(d,o,T),t*(T+.2),U)+vec3(.7*pow(clamp(dot(normalize(m),i),0.,1.),12.)),h+=C*mix(F*V,g,Z/w),C*=b*(1.-Z/w),X=.1):"
-         "(h+=C*g,C=0.);"
-     "}"
+   "for(;C>.1;Z<w?"
+     "(p+=i*Z,W=e(p),U=f,F=normalize(-vec3(W-e(p+u.xyy),W-e(p+u.yxy),W-e(p+u.yyx))),V=clamp(e(p+F*.05)*4.+e(p+F*.1)*2.+.5,.1,1.),b=U*.3,F=normalize(F+step(4.,v)*f*sin(p.yzx*40.)*.05),i=reflect(i,F),T=clamp(dot(normalize(m),F),0.,1.),F=mix(mix(d,o,T),t*(T+.2),U)+vec3(.7*pow(clamp(dot(normalize(m),i),0.,1.),12.)),h+=C*mix(F*V,g,Z/w),C*=b*(1.-Z/w),X=.1):"
+     "(h+=C*g,C=0.))"
+     "for(Z=X,Y=1.;Z<w&&Y>.005;Z+=Y)"
+       "Y=e(p+i*Z);"
    "gl_FragColor.xyz=h;"
    "gl_FragColor.w=1.;"
  "}";

tests/unit/blocks.expected

@@ -33,8 +33,7 @@ const char *blocks_frag =
  "}"
  "int test_block()"
  "{"
-   "if(k==0)"
-     ";"
+   "k==0;"
    "for(int i=0;i<2;i++)"
      "{"
        "if(k==1)"
@@ -72,10 +71,8 @@ const char *blocks_frag =
    "removeUselessElseAfterReturn2(0.);"
    "replaceIfReturnsByReturnTernary1(0.);"
    "gl_FragColor=vec4(.2,a,b,0);"
-   "if(a<b)"
-     ";"
-   "if(a<b)"
-     ";"
+   "a<b;"
+   "a<b;"
  "}";
 
 #endif // BLOCKS_EXPECTED_

tests/unit/inline-aggro.aggro.expected

@@ -113,7 +113,7 @@ int noinl11(ivec3 x)
 int noinl12()
 {
   int i=10;
-  while(--i>0)
+  for(;--i>0;)
     ;
   return 1;
 }

tests/unit/inline-aggro.expected

@@ -120,7 +120,7 @@ int noinl11(ivec3 x)
 int noinl12()
 {
   int i=10;
-  while(--i>0)
+  for(;--i>0;)
     ;
   return 1;
 }

tests/unit/loop.frag

@@ -0,0 +1,48 @@
+float f(){return 0.;}
+void main()
+{
+	float c;
+	for (float a=0; a<50.; ++a)
+	{
+		c+=cos(a);
+	}
+	float b;
+	for (b=0; b<50.; ++b)
+	{
+		c+=cos(c);
+	}
+	b = a;
+	while (b<50.)
+	{
+		c+=cos(c);
+		b++;
+	}
+	b = a;
+	while (b<50.)
+	{
+		b++;
+	}
+	b = a;
+	while (b<50.)
+	{
+		c+=cos(c);
+		float d=f(); // d prevents moving b+=d to a for
+		b+=d;
+	}
+	b = a;
+	while (b<50.)
+	{
+		if (a < b) continue; // continue prevents moving b++ to a for
+		b++;
+	}
+	b = a;
+	while (b<50.)
+	{
+		if (a < b) a=b; else continue; // continue prevents moving b++ to a for
+		b++;
+	}
+	for (; b<50.; ++b)
+	{
+		c+=cos(b);
+	}
+}

tests/unit/loop.frag.expected

@@ -0,0 +1,47 @@
+/* File generated with 
+ * http://www.ctrl-alt-test.fr
+ */
+#ifndef LOOP_FRAG_EXPECTED_
+# define LOOP_FRAG_EXPECTED_
+
+const char *loop_frag =
+ "float f()"
+ "{"
+   "return 0.;"
+ "}"
+ "void main()"
+ "{"
+   "float c,b;"
+   "for(float a=0;a<50.;++a)"
+     "c+=cos(a);"
+   "for(b=0;b<50.;++b)"
+     "c+=cos(c);"
+   "for(b=a;b<50.;b++)"
+     "c+=cos(c);"
+   "for(b=a;b<50.;b++)"
+     ";"
+   "for(b=a;b<50.;)"
+     "{"
+       "c+=cos(c);"
+       "float d=f();"
+       "b+=d;"
+     "}"
+   "for(b=a;b<50.;)"
+     "{"
+       "if(a<b)"
+         "continue;"
+       "b++;"
+     "}"
+   "for(b=a;b<50.;)"
+     "{"
+       "if(a<b)"
+         "a=b;"
+       "else"
+         " continue;"
+       "b++;"
+     "}"
+   "for(;b<50.;++b)"
+     "c+=cos(b);"
+ "}";
+
+#endif // LOOP_FRAG_EXPECTED_