cmd/compile: improve integer comparisons with numeric bounds

This do:
- Fold always false or always true comparisons for ints and uint.
- Reduce < and <= where the true set is only one value to == with such value.

Change-Id: Ie9e3f70efd1845bef62db56543f051a50ad2532e
Reviewed-on: https://go-review.googlesource.com/c/go/+/555135
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

2 files changed, 20 insertions, 11 deletions

diff --git a/test/fuse.go b/test/fuse.go
index f64a087965..e9205dcc23 100644
--- a/test/fuse.go
+++ b/test/fuse.go
@@ -33,7 +33,7 @@ func fEqLessU(a uint, f float64) bool {
 }
 
 func fEqLeqU(a uint64, f float64) bool {
-	return a == 0 && f > Cf2 || a <= 0 && f < -Cf2 // ERROR "Redirect Leq64U based on Eq64$"
+	return a == 0 && f > Cf2 || a <= 0 && f < -Cf2 // ERROR "Redirect Eq64 based on Eq64$"
 }
 
 func fNeqEq(a int, f float64) bool {
@@ -58,7 +58,7 @@ func fNeqLessU(a uint, f float64) bool {
 }
 
 func fNeqLeqU(a uint32, f float64) bool {
-	return a != 0 && f > Cf2 || a <= 0 && f < -Cf2 // ERROR "Redirect Leq32U based on Neq32$"
+	return a != 2 && f > Cf2 || a <= 2 && f < -Cf2 // ERROR "Redirect Leq32U based on Neq32$"
 }
 
 func fLessEq(a int, f float64) bool {
@@ -110,11 +110,11 @@ func fLessULeqU(a uint64, f float64) bool {
 }
 
 func fLeqUEq(a uint8, f float64) bool {
-	return a <= 0 && f > Cf2 || a == 0 && f < -Cf2 // ERROR "Redirect Eq8 based on Leq8U$"
+	return a <= 2 && f > Cf2 || a == 2 && f < -Cf2 // ERROR "Redirect Eq8 based on Leq8U$"
 }
 
 func fLeqUNeq(a uint16, f float64) bool {
-	return a <= 0 && f > Cf2 || a != 0 && f < -Cf2 // ERROR "Redirect Neq16 based on Leq16U$"
+	return a <= 2 && f > Cf2 || a != 2 && f < -Cf2 // ERROR "Redirect Neq16 based on Leq16U$"
 }
 
 func fLeqLessU(a uint32, f float64) bool {
@@ -122,7 +122,7 @@ func fLeqLessU(a uint32, f float64) bool {
 }
 
 func fLeqLeqU(a uint64, f float64) bool {
-	return a <= 0 && f > Cf2 || a <= 0 && f < -Cf2 // ERROR "Redirect Leq64U based on Leq64U$"
+	return a <= 2 && f > Cf2 || a <= 2 && f < -Cf2 // ERROR "Redirect Leq64U based on Leq64U$"
 }
 
 // Arg tests are disabled because the op name is different on amd64 and arm64.
diff --git a/test/prove.go b/test/prove.go
index 1aea282291..0d93db905a 100644
--- a/test/prove.go
+++ b/test/prove.go
@@ -396,8 +396,11 @@ func f13e(a int) int {
 	return 0
 }
 
-func f13f(a int64) int64 {
-	if a > math.MaxInt64 {
+func f13f(a, b int64) int64 {
+	if b != math.MaxInt64 {
+		return 42
+	}
+	if a > b {
 		if a == 0 { // ERROR "Disproved Eq64$"
 			return 1
 		}
@@ -869,9 +872,12 @@ func unrollInclStepTooLarge(a []int) int {
 }
 
 // Not an induction variable (min too small, iterating down)
-func unrollDecMin(a []int) int {
+func unrollDecMin(a []int, b int) int {
+	if b != math.MinInt64 {
+		return 42
+	}
 	var i, x int
-	for i = len(a); i >= math.MinInt64; i -= 2 {
+	for i = len(a); i >= b; i -= 2 {
 		x += a[i-1]
 		x += a[i-2]
 	}
@@ -882,9 +888,12 @@ func unrollDecMin(a []int) int {
 }
 
 // Not an induction variable (min too small, iterating up -- perhaps could allow, but why bother?)
-func unrollIncMin(a []int) int {
+func unrollIncMin(a []int, b int) int {
+	if b != math.MinInt64 {
+		return 42
+	}
 	var i, x int
-	for i = len(a); i >= math.MinInt64; i += 2 {
+	for i = len(a); i >= b; i += 2 {
 		x += a[i-1]
 		x += a[i-2]
 	}