cmd/compile: make loopbce handle 8, 16 and 32 bit induction variables

Compute limits and increment values for all integer widths.
Resolves 2 TODO's in loopbce.go

compilecmp linux/amd64:

compress/flate
compress/flate.(*huffmanEncoder).bitCounts 1235 -> 1207  (-2.27%)

cmd/internal/obj/wasm
cmd/internal/obj/wasm.assemble 7443 -> 7303  (-1.88%)
cmd/internal/obj/wasm.assemble.func1 165 -> 138  (-16.36%)

cmd/link/internal/ld
cmd/link/internal/ld.(*Link).findfunctab.func1 1646 -> 1627  (-1.15%)

Change-Id: I2d79b7376eb67d6bcc8fdaf0c197c11e631562d0
Reviewed-on: https://go-review.googlesource.com/c/go/+/435258
Reviewed-by: Benny Siegert <bsiegert@gmail.com>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/test/loopbce.go b/test/loopbce.go
index db830daf5c..fcf0d8d90d 100644
--- a/test/loopbce.go
+++ b/test/loopbce.go
@@ -63,6 +63,30 @@ func f5(a [10]int) int {
 	return x
 }
 
+func f5_int32(a [10]int) int {
+	x := 0
+	for i := int32(-10); i < int32(len(a)); i += 2 { // ERROR "Induction variable: limits \[-10,8\], increment 2$"
+		x += a[i]
+	}
+	return x
+}
+
+func f5_int16(a [10]int) int {
+	x := 0
+	for i := int16(-10); i < int16(len(a)); i += 2 { // ERROR "Induction variable: limits \[-10,8\], increment 2$"
+		x += a[i]
+	}
+	return x
+}
+
+func f5_int8(a [10]int) int {
+	x := 0
+	for i := int8(-10); i < int8(len(a)); i += 2 { // ERROR "Induction variable: limits \[-10,8\], increment 2$"
+		x += a[i]
+	}
+	return x
+}
+
 func f6(a []int) {
 	for i := range a { // ERROR "Induction variable: limits \[0,\?\), increment 1$"
 		b := a[0:i] // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"