remove special-case lowering for for i = a:b loops (ref #5355)

this fixes some edge-case loops that the special lowering did not
handle correctly.

colon() now checks for overflow in computing the length, which avoids
some buggy Range1s that used to be possible.

this required some changes to make sure Range1 is fast enough:
specialized start, done, next, and a hack to avoid one of the checks and
allow better inlining.

in general performance is about the same, but a few cases are actually
faster, since Range1 is now faster (comprehensions used Range1 instead
of the special-case lowering, for example). also, more loops should be
vectorizable when the appropriate LLVM passes are enabled. all that
plus better correctness and a simpler front-end, and I'm sold.

Author: JeffBezanson

Diff for: base/range.jl

@@ -24,19 +24,38 @@ immutable Range1{T<:Real} <: Ranges{T}
     len::Int
 
     function Range1(start::T, len::Int)
-        if !(len >= 0); error("length must be non-negative"); end
+        if len < 0; error("length must be non-negative"); end
         new(start, len)
     end
     Range1(start::T, len::Integer) = Range1(start, int(len))
+
+    # TODO: this is a hack to elide the len<0 check for colon.
+    # should store start and stop for integer ranges instead
+    Range1(start::T, len::Integer, _) = new(start, int(len))
 end
 Range1{T}(start::T, len::Integer) = Range1{T}(start, len)
 
 function colon{T<:Integer}(start::T, step::T, stop::T)
     step != 0 || error("step cannot be zero in colon syntax")
-    Range(start, step, max(0, 1 + fld(stop-start, step)))
+    Range{T}(start, step, max(0, 1 + fld(stop-start, step)))
 end
+
 colon{T<:Integer}(start::T, stop::T) =
-    Range1(start, max(0, stop-start+1))
+    Range1{T}(start, ifelse(stop<start, 0, int(stop-start+1)))
+
+if Int === Int32
+colon{T<:Union(Int8,Int16,Int32,Uint8,Uint16)}(start::T, stop::T) =
+    Range1{T}(start,
+              ifelse(stop<start, 0,
+                     checked_add(checked_sub(convert(Int,stop),convert(Int,start)),1)),
+              0)  # hack to elide negative length check
+else
+colon{T<:Union(Int8,Int16,Int32,Int64,Uint8,Uint16,Uint32)}(start::T, stop::T) =
+    Range1{T}(start,
+              ifelse(stop<start, 0,
+                     checked_add(checked_sub(convert(Int,stop),convert(Int,start)),1)),
+              0)  # hack to elide negative length check
+end
 
 function colon{T<:Real}(start::T, step::T, stop::T)
     step != 0 || error("step cannot be zero in colon syntax")
@@ -151,6 +170,12 @@ next{T}(r::Range{T},  i) = (oftype(T, r.start + i*step(r)), i+1)
 next{T}(r::Range1{T}, i) = (oftype(T, r.start + i), i+1)
 done(r::Ranges, i) = (length(r) <= i)
 
+# though these look very similar to the above, for some reason LLVM generates
+# much better code for these.
+start{T<:Integer}(r::Range1{T}) = r.start
+next{T<:Integer}(r::Range1{T}, i) = (i, oftype(T, i+1))
+done{T<:Integer}(r::Range1{T}, i) = i==(r.start+r.len)
+
 ==(r::Ranges, s::Ranges) = (r.start==s.start) & (step(r)==step(s)) & (r.len==s.len)
 ==(r::Range1, s::Range1) = (r.start==s.start) & (r.len==s.len)
 

Diff for: src/julia-syntax.scm

@@ -1722,46 +1722,22 @@
      (let ((X (caddr (cadr e)))
 	   (lhs (cadr (cadr e)))
 	   (body (caddr e)))
-       (if
-	(and (pair? X) (eq? (car X) ':) (length= X 3))
-	;; (for (= lhs (: a b)) body)
-	(let* ((cnt (gensy))
-	       (a (cadr X))
-	       (b (caddr X))
-	       (lim (if (number? b) b (gensy))))
-	  `(scope-block
-	    (block
-	     (= ,cnt ,(expand-forms a))
-	     ,.(if (eq? lim b) '() `((= ,lim ,(expand-forms b))))
-	     (break-block loop-exit
-			  (_while (call (top <=) ,cnt ,lim)
-				  (scope-block
-				   (block
-				    ;; NOTE: enable this to force loop-local var
-				    #;(local ,lhs)
-				    (= ,lhs ,cnt)
-				    (break-block loop-cont
-						 ,(expand-forms body))
-				    (= ,cnt (call (top convert)
-						  (call (top typeof) ,cnt)
-						  (call (top +) 1 ,cnt))))))))))
-
-	;; (for (= lhs X) body)
-	(let ((coll  (gensy))
-	      (state (gensy)))
-	  `(scope-block
-	    (block (= ,coll ,(expand-forms X))
-		   (= ,state (call (top start) ,coll))
-		   ,(expand-forms
-		     `(while
-		       (call (top !) (call (top done) ,coll ,state))
-		       (scope-block
-			(block
-			 ;; NOTE: enable this to force loop-local var
-			 #;,@(map (lambda (v) `(local ,v)) (lhs-vars lhs))
-			 ,(lower-tuple-assignment (list lhs state)
-						  `(call (top next) ,coll ,state))
-			 ,body))))))))))
+       ;; (for (= lhs X) body)
+       (let ((coll  (gensy))
+	     (state (gensy)))
+	 `(scope-block
+	   (block (= ,coll ,(expand-forms X))
+		  (= ,state (call (top start) ,coll))
+		  ,(expand-forms
+		    `(while
+		      (call (top !) (call (top done) ,coll ,state))
+		      (scope-block
+		       (block
+			;; NOTE: enable this to force loop-local var
+			#;,@(map (lambda (v) `(local ,v)) (lhs-vars lhs))
+			,(lower-tuple-assignment (list lhs state)
+						 `(call (top next) ,coll ,state))
+			,body)))))))))
 
    '+=     lower-update-op
    '-=     lower-update-op

Diff for: test/ranges.jl

@@ -103,3 +103,50 @@ r = (-4*int64(maxintfloat(is(Int,Int32) ? Float32 : Float64))):5
 
 # avoiding intermediate overflow (#5065)
 @test length(1:4:typemax(Int)) == div(typemax(Int),4) + 1
+
+# overflow in length
+@test_throws 0:typemax(Int)
+@test_throws typemin(Int):typemax(Int)
+@test_throws -1:typemax(Int)-1
+
+# parity between ranges and for loops (see issue #5355)
+
+@test length(2.0^53:(2.0^53+2)) == 3
+let s = 0
+    r = 2.0^53:(2.0^53+2)
+    for i in r
+        s += 1
+        @test s <= 3
+    end
+    @test s == 3
+
+    s = 0
+    for i in 2.0^53:(2.0^53+2)
+        s += 1
+        @test s <= 3
+    end
+    @test s == 3
+end
+
+let s = 0
+    # loops ending at typemax(Int)
+    for i = (typemax(Int)-1):typemax(Int)
+        s += 1
+        @test s <= 2
+    end
+    @test s == 2
+
+    s = 0
+    for i = (typemax(Int)-2):(typemax(Int)-1)
+        s += 1
+        @test s <= 2
+    end
+    @test s == 2
+
+    s = 0
+    for i = typemin(Int):(typemin(Int)+1)
+        s += 1
+        @test s <= 2
+    end
+    @test s == 2
+end