cmd/compile: clean up codegen for branch-on-carry on s390x

This CL optimizes code that uses a carry from a function such as
bits.Add64 as the condition in an if statement. For example:

    x, c := bits.Add64(a, b, 0)
    if c != 0 {
        panic("overflow")
    }

Rather than converting the carry into a 0 or a 1 value and using
that as an input to a comparison instruction the carry flag is now
used as the input to a conditional branch directly. This typically
removes an ADD LOGICAL WITH CARRY instruction when user code is
doing overflow detection and is closer to the code that a user
would expect to generate.

Change-Id: I950431270955ab72f1b5c6db873b6abe769be0da
Reviewed-on: https://go-review.googlesource.com/c/go/+/219757
Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

1 files changed, 126 insertions, 0 deletions

diff --git a/test/codegen/mathbits.go b/test/codegen/mathbits.go
index 8bd6242b1e..942605de55 100644
--- a/test/codegen/mathbits.go
+++ b/test/codegen/mathbits.go
@@ -472,6 +472,69 @@ func Add64M(p, q, r *[3]uint64) {
 	r[2], c = bits.Add64(p[2], q[2], c)
 }
 
+func Add64PanicOnOverflowEQ(a, b uint64) uint64 {
+	r, c := bits.Add64(a, b, 0)
+	// s390x:"BRC\t[$]3,",-"ADDE"
+	if c == 1 {
+		panic("overflow")
+	}
+	return r
+}
+
+func Add64PanicOnOverflowNE(a, b uint64) uint64 {
+	r, c := bits.Add64(a, b, 0)
+	// s390x:"BRC\t[$]3,",-"ADDE"
+	if c != 0 {
+		panic("overflow")
+	}
+	return r
+}
+
+func Add64PanicOnOverflowGT(a, b uint64) uint64 {
+	r, c := bits.Add64(a, b, 0)
+	// s390x:"BRC\t[$]3,",-"ADDE"
+	if c > 0 {
+		panic("overflow")
+	}
+	return r
+}
+
+func Add64MPanicOnOverflowEQ(a, b [2]uint64) [2]uint64 {
+	var r [2]uint64
+	var c uint64
+	r[0], c = bits.Add64(a[0], b[0], c)
+	r[1], c = bits.Add64(a[1], b[1], c)
+	// s390x:"BRC\t[$]3,"
+	if c == 1 {
+		panic("overflow")
+	}
+	return r
+}
+
+func Add64MPanicOnOverflowNE(a, b [2]uint64) [2]uint64 {
+	var r [2]uint64
+	var c uint64
+	r[0], c = bits.Add64(a[0], b[0], c)
+	r[1], c = bits.Add64(a[1], b[1], c)
+	// s390x:"BRC\t[$]3,"
+	if c != 0 {
+		panic("overflow")
+	}
+	return r
+}
+
+func Add64MPanicOnOverflowGT(a, b [2]uint64) [2]uint64 {
+	var r [2]uint64
+	var c uint64
+	r[0], c = bits.Add64(a[0], b[0], c)
+	r[1], c = bits.Add64(a[1], b[1], c)
+	// s390x:"BRC\t[$]3,"
+	if c > 0 {
+		panic("overflow")
+	}
+	return r
+}
+
 // --------------- //
 //    bits.Sub*    //
 // --------------- //
@@ -552,6 +615,69 @@ func Sub64M(p, q, r *[3]uint64) {
 	r[2], c = bits.Sub64(p[2], q[2], c)
 }
 
+func Sub64PanicOnOverflowEQ(a, b uint64) uint64 {
+	r, b := bits.Sub64(a, b, 0)
+	// s390x:"BRC\t[$]12,",-"ADDE",-"SUBE"
+	if b == 1 {
+		panic("overflow")
+	}
+	return r
+}
+
+func Sub64PanicOnOverflowNE(a, b uint64) uint64 {
+	r, b := bits.Sub64(a, b, 0)
+	// s390x:"BRC\t[$]12,",-"ADDE",-"SUBE"
+	if b != 0 {
+		panic("overflow")
+	}
+	return r
+}
+
+func Sub64PanicOnOverflowGT(a, b uint64) uint64 {
+	r, b := bits.Sub64(a, b, 0)
+	// s390x:"BRC\t[$]12,",-"ADDE",-"SUBE"
+	if b > 0 {
+		panic("overflow")
+	}
+	return r
+}
+
+func Sub64MPanicOnOverflowEQ(a, b [2]uint64) [2]uint64 {
+	var r [2]uint64
+	var c uint64
+	r[0], c = bits.Sub64(a[0], b[0], c)
+	r[1], c = bits.Sub64(a[1], b[1], c)
+	// s390x:"BRC\t[$]12,"
+	if c == 1 {
+		panic("overflow")
+	}
+	return r
+}
+
+func Sub64MPanicOnOverflowNE(a, b [2]uint64) [2]uint64 {
+	var r [2]uint64
+	var c uint64
+	r[0], c = bits.Sub64(a[0], b[0], c)
+	r[1], c = bits.Sub64(a[1], b[1], c)
+	// s390x:"BRC\t[$]12,"
+	if c != 0 {
+		panic("overflow")
+	}
+	return r
+}
+
+func Sub64MPanicOnOverflowGT(a, b [2]uint64) [2]uint64 {
+	var r [2]uint64
+	var c uint64
+	r[0], c = bits.Sub64(a[0], b[0], c)
+	r[1], c = bits.Sub64(a[1], b[1], c)
+	// s390x:"BRC\t[$]12,"
+	if c > 0 {
+		panic("overflow")
+	}
+	return r
+}
+
 // --------------- //
 //    bits.Mul*    //
 // --------------- //