cmd/compile: sparse conditional constant propagation

sparse conditional constant propagation can discover optimization opportunities that cannot be found by just combining constant folding and constant propagation and dead code elimination separately.

Updates #59399

Change-Id: Ia954e906480654a6f0cc065d75b5912f96f36b2e
GitHub-Last-Rev: 90fc02db99f817b7f0ce5c584642ab1b166e62d7
GitHub-Pull-Request: golang/go#59575
Reviewed-on: https://go-review.googlesource.com/c/go/+/483875
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Michael Pratt <mpratt@google.com>
Run-TryBot: Keith Randall <khr@golang.org>

3 files changed, 38 insertions, 11 deletions

diff --git a/test/checkbce.go b/test/checkbce.go
index 6a126099bc..ab31d95283 100644
--- a/test/checkbce.go
+++ b/test/checkbce.go
@@ -137,6 +137,10 @@ func g4(a [100]int) {
 		useInt(a[i+50])
 
 		// The following are out of bounds.
+		if a[0] == 0xdeadbeef {
+			// This is a trick to prohibit sccp to optimize out the following out of bound check
+			continue
+		}
 		useInt(a[i-11]) // ERROR "Found IsInBounds$"
 		useInt(a[i+51]) // ERROR "Found IsInBounds$"
 	}
diff --git a/test/codegen/compare_and_branch.go b/test/codegen/compare_and_branch.go
index b3feef0eb7..479bd318be 100644
--- a/test/codegen/compare_and_branch.go
+++ b/test/codegen/compare_and_branch.go
@@ -35,12 +35,12 @@ func si64x8() {
 	}
 
 	// s390x:"CGIJ\t[$]2, R[0-9]+, [$]127, "
-	for i := int64(0); i >= 128; i++ {
+	for i := int64(129); i >= 128; i-- {
 		dummy()
 	}
 
 	// s390x:"CGIJ\t[$]4, R[0-9]+, [$]-128, "
-	for i := int64(0); i <= -129; i-- {
+	for i := int64(-130); i <= -129; i++ {
 		dummy()
 	}
 }
@@ -71,7 +71,7 @@ func ui64x8() {
 	}
 
 	// s390x:"CLGIJ\t[$]2, R[0-9]+, [$]255, "
-	for i := uint64(0); i >= 256; i-- {
+	for i := uint64(257); i >= 256; i-- {
 		dummy()
 	}
 
@@ -107,12 +107,12 @@ func si32x8() {
 	}
 
 	// s390x:"CIJ\t[$]2, R[0-9]+, [$]127, "
-	for i := int32(0); i >= 128; i++ {
+	for i := int32(129); i >= 128; i-- {
 		dummy()
 	}
 
 	// s390x:"CIJ\t[$]4, R[0-9]+, [$]-128, "
-	for i := int32(0); i <= -129; i-- {
+	for i := int32(-130); i <= -129; i++ {
 		dummy()
 	}
 }
@@ -143,7 +143,7 @@ func ui32x8() {
 	}
 
 	// s390x:"CLIJ\t[$]2, R[0-9]+, [$]255, "
-	for i := uint32(0); i >= 256; i-- {
+	for i := uint32(257); i >= 256; i-- {
 		dummy()
 	}
 
diff --git a/test/loopbce.go b/test/loopbce.go
index fcf0d8d90d..1119aaa65a 100644
--- a/test/loopbce.go
+++ b/test/loopbce.go
@@ -58,7 +58,7 @@ func f4(a [10]int) int {
 func f5(a [10]int) int {
 	x := 0
 	for i := -10; i < len(a); i += 2 { // ERROR "Induction variable: limits \[-10,8\], increment 2$"
-		x += a[i]
+		x += a[i+10]
 	}
 	return x
 }
@@ -66,7 +66,7 @@ func f5(a [10]int) int {
 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]
+		x += a[i+10]
 	}
 	return x
 }
@@ -74,7 +74,7 @@ func f5_int32(a [10]int) int {
 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]
+		x += a[i+10]
 	}
 	return x
 }
@@ -82,7 +82,7 @@ func f5_int16(a [10]int) int {
 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]
+		x += a[i+10]
 	}
 	return x
 }
@@ -201,6 +201,10 @@ func h2(a []byte) {
 
 func k0(a [100]int) [100]int {
 	for i := 10; i < 90; i++ { // ERROR "Induction variable: limits \[10,90\), increment 1$"
+		if a[0] == 0xdeadbeef {
+			// This is a trick to prohibit sccp to optimize out the following out of bound check
+			continue
+		}
 		a[i-11] = i
 		a[i-10] = i // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 		a[i-5] = i  // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
@@ -214,6 +218,10 @@ func k0(a [100]int) [100]int {
 
 func k1(a [100]int) [100]int {
 	for i := 10; i < 90; i++ { // ERROR "Induction variable: limits \[10,90\), increment 1$"
+		if a[0] == 0xdeadbeef {
+			// This is a trick to prohibit sccp to optimize out the following out of bound check
+			continue
+		}
 		useSlice(a[:i-11])
 		useSlice(a[:i-10]) // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
 		useSlice(a[:i-5])  // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
@@ -229,6 +237,10 @@ func k1(a [100]int) [100]int {
 
 func k2(a [100]int) [100]int {
 	for i := 10; i < 90; i++ { // ERROR "Induction variable: limits \[10,90\), increment 1$"
+		if a[0] == 0xdeadbeef {
+			// This is a trick to prohibit sccp to optimize out the following out of bound check
+			continue
+		}
 		useSlice(a[i-11:])
 		useSlice(a[i-10:]) // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
 		useSlice(a[i-5:])  // ERROR "(\([0-9]+\) )?Proved IsSliceInBounds$"
@@ -243,6 +255,10 @@ func k2(a [100]int) [100]int {
 
 func k3(a [100]int) [100]int {
 	for i := -10; i < 90; i++ { // ERROR "Induction variable: limits \[-10,90\), increment 1$"
+		if a[0] == 0xdeadbeef {
+			// This is a trick to prohibit sccp to optimize out the following out of bound check
+			continue
+		}
 		a[i+9] = i
 		a[i+10] = i // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 		a[i+11] = i
@@ -252,6 +268,10 @@ func k3(a [100]int) [100]int {
 
 func k3neg(a [100]int) [100]int {
 	for i := 89; i > -11; i-- { // ERROR "Induction variable: limits \(-11,89\], increment 1$"
+		if a[0] == 0xdeadbeef {
+			// This is a trick to prohibit sccp to optimize out the following out of bound check
+			continue
+		}
 		a[i+9] = i
 		a[i+10] = i // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 		a[i+11] = i
@@ -261,6 +281,10 @@ func k3neg(a [100]int) [100]int {
 
 func k3neg2(a [100]int) [100]int {
 	for i := 89; i >= -10; i-- { // ERROR "Induction variable: limits \[-10,89\], increment 1$"
+		if a[0] == 0xdeadbeef {
+			// This is a trick to prohibit sccp to optimize out the following out of bound check
+			continue
+		}
 		a[i+9] = i
 		a[i+10] = i // ERROR "(\([0-9]+\) )?Proved IsInBounds$"
 		a[i+11] = i
@@ -411,7 +435,6 @@ func nobce3(a [100]int64) [100]int64 {
 	min := int64((-1) << 63)
 	max := int64((1 << 63) - 1)
 	for i := min; i < max; i++ { // ERROR "Induction variable: limits \[-9223372036854775808,9223372036854775807\), increment 1$"
-		a[i] = i
 	}
 	return a
 }