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>

4 files changed, 604 insertions, 0 deletions

diff --git a/src/cmd/compile/internal/ssa/gen/S390X.rules b/src/cmd/compile/internal/ssa/gen/S390X.rules
index 7e713303af..61ba4ac38e 100644
--- a/src/cmd/compile/internal/ssa/gen/S390X.rules
+++ b/src/cmd/compile/internal/ssa/gen/S390X.rules
@@ -1218,6 +1218,20 @@
 (SUBE x y (Select1 (SUBC (MOVDconst [0]) (NEG (Select0 (SUBE (MOVDconst [0]) (MOVDconst [0]) c))))))
   -> (SUBE x y c)
 
+// branch on carry
+(C(G|LG)IJ {s390x.Equal}         (Select0 (ADDE (MOVDconst [0]) (MOVDconst [0]) carry)) [0]) => (BRC {s390x.NoCarry} carry)
+(C(G|LG)IJ {s390x.Equal}         (Select0 (ADDE (MOVDconst [0]) (MOVDconst [0]) carry)) [1]) => (BRC {s390x.Carry}   carry)
+(C(G|LG)IJ {s390x.LessOrGreater} (Select0 (ADDE (MOVDconst [0]) (MOVDconst [0]) carry)) [0]) => (BRC {s390x.Carry}   carry)
+(C(G|LG)IJ {s390x.LessOrGreater} (Select0 (ADDE (MOVDconst [0]) (MOVDconst [0]) carry)) [1]) => (BRC {s390x.NoCarry} carry)
+(C(G|LG)IJ {s390x.Greater}       (Select0 (ADDE (MOVDconst [0]) (MOVDconst [0]) carry)) [0]) => (BRC {s390x.Carry}   carry)
+
+// branch on borrow
+(C(G|LG)IJ {s390x.Equal}         (NEG (Select0 (SUBE (MOVDconst [0]) (MOVDconst [0]) borrow))) [0]) => (BRC {s390x.NoBorrow} borrow)
+(C(G|LG)IJ {s390x.Equal}         (NEG (Select0 (SUBE (MOVDconst [0]) (MOVDconst [0]) borrow))) [1]) => (BRC {s390x.Borrow}   borrow)
+(C(G|LG)IJ {s390x.LessOrGreater} (NEG (Select0 (SUBE (MOVDconst [0]) (MOVDconst [0]) borrow))) [0]) => (BRC {s390x.Borrow}   borrow)
+(C(G|LG)IJ {s390x.LessOrGreater} (NEG (Select0 (SUBE (MOVDconst [0]) (MOVDconst [0]) borrow))) [1]) => (BRC {s390x.NoBorrow} borrow)
+(C(G|LG)IJ {s390x.Greater}       (NEG (Select0 (SUBE (MOVDconst [0]) (MOVDconst [0]) borrow))) [0]) => (BRC {s390x.Borrow}   borrow)
+
 // fused multiply-add
 (Select0 (F(ADD|SUB) (FMUL y z) x)) -> (FM(ADD|SUB) x y z)
 (Select0 (F(ADDS|SUBS) (FMULS y z) x)) -> (FM(ADDS|SUBS) x y z)
diff --git a/src/cmd/compile/internal/ssa/rewriteS390X.go b/src/cmd/compile/internal/ssa/rewriteS390X.go
index 01b654ac95..a7f6b3cd9c 100644
--- a/src/cmd/compile/internal/ssa/rewriteS390X.go
+++ b/src/cmd/compile/internal/ssa/rewriteS390X.go
@@ -19678,6 +19678,236 @@ func rewriteBlockS390X(b *Block) bool {
 			b.swapSuccessors()
 			return true
 		}
+		// match: (CGIJ {s390x.Equal} (Select0 (ADDE (MOVDconst [0]) (MOVDconst [0]) carry)) [0])
+		// result: (BRC {s390x.NoCarry} carry)
+		for b.Controls[0].Op == OpSelect0 {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpS390XADDE {
+				break
+			}
+			carry := v_0_0.Args[2]
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_1 := v_0_0.Args[1]
+			if v_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_1.AuxInt) != 0 || auxIntToInt8(b.AuxInt) != 0 || auxToS390xCCMask(b.Aux) != s390x.Equal {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, carry)
+			b.Aux = s390xCCMaskToAux(s390x.NoCarry)
+			return true
+		}
+		// match: (CGIJ {s390x.Equal} (Select0 (ADDE (MOVDconst [0]) (MOVDconst [0]) carry)) [1])
+		// result: (BRC {s390x.Carry} carry)
+		for b.Controls[0].Op == OpSelect0 {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpS390XADDE {
+				break
+			}
+			carry := v_0_0.Args[2]
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_1 := v_0_0.Args[1]
+			if v_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_1.AuxInt) != 0 || auxIntToInt8(b.AuxInt) != 1 || auxToS390xCCMask(b.Aux) != s390x.Equal {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, carry)
+			b.Aux = s390xCCMaskToAux(s390x.Carry)
+			return true
+		}
+		// match: (CGIJ {s390x.LessOrGreater} (Select0 (ADDE (MOVDconst [0]) (MOVDconst [0]) carry)) [0])
+		// result: (BRC {s390x.Carry} carry)
+		for b.Controls[0].Op == OpSelect0 {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpS390XADDE {
+				break
+			}
+			carry := v_0_0.Args[2]
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_1 := v_0_0.Args[1]
+			if v_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_1.AuxInt) != 0 || auxIntToInt8(b.AuxInt) != 0 || auxToS390xCCMask(b.Aux) != s390x.LessOrGreater {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, carry)
+			b.Aux = s390xCCMaskToAux(s390x.Carry)
+			return true
+		}
+		// match: (CGIJ {s390x.LessOrGreater} (Select0 (ADDE (MOVDconst [0]) (MOVDconst [0]) carry)) [1])
+		// result: (BRC {s390x.NoCarry} carry)
+		for b.Controls[0].Op == OpSelect0 {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpS390XADDE {
+				break
+			}
+			carry := v_0_0.Args[2]
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_1 := v_0_0.Args[1]
+			if v_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_1.AuxInt) != 0 || auxIntToInt8(b.AuxInt) != 1 || auxToS390xCCMask(b.Aux) != s390x.LessOrGreater {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, carry)
+			b.Aux = s390xCCMaskToAux(s390x.NoCarry)
+			return true
+		}
+		// match: (CGIJ {s390x.Greater} (Select0 (ADDE (MOVDconst [0]) (MOVDconst [0]) carry)) [0])
+		// result: (BRC {s390x.Carry} carry)
+		for b.Controls[0].Op == OpSelect0 {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpS390XADDE {
+				break
+			}
+			carry := v_0_0.Args[2]
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_1 := v_0_0.Args[1]
+			if v_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_1.AuxInt) != 0 || auxIntToInt8(b.AuxInt) != 0 || auxToS390xCCMask(b.Aux) != s390x.Greater {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, carry)
+			b.Aux = s390xCCMaskToAux(s390x.Carry)
+			return true
+		}
+		// match: (CGIJ {s390x.Equal} (NEG (Select0 (SUBE (MOVDconst [0]) (MOVDconst [0]) borrow))) [0])
+		// result: (BRC {s390x.NoBorrow} borrow)
+		for b.Controls[0].Op == OpS390XNEG {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpSelect0 {
+				break
+			}
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XSUBE {
+				break
+			}
+			borrow := v_0_0_0.Args[2]
+			v_0_0_0_0 := v_0_0_0.Args[0]
+			if v_0_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_0_1 := v_0_0_0.Args[1]
+			if v_0_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_1.AuxInt) != 0 || auxIntToInt8(b.AuxInt) != 0 || auxToS390xCCMask(b.Aux) != s390x.Equal {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, borrow)
+			b.Aux = s390xCCMaskToAux(s390x.NoBorrow)
+			return true
+		}
+		// match: (CGIJ {s390x.Equal} (NEG (Select0 (SUBE (MOVDconst [0]) (MOVDconst [0]) borrow))) [1])
+		// result: (BRC {s390x.Borrow} borrow)
+		for b.Controls[0].Op == OpS390XNEG {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpSelect0 {
+				break
+			}
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XSUBE {
+				break
+			}
+			borrow := v_0_0_0.Args[2]
+			v_0_0_0_0 := v_0_0_0.Args[0]
+			if v_0_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_0_1 := v_0_0_0.Args[1]
+			if v_0_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_1.AuxInt) != 0 || auxIntToInt8(b.AuxInt) != 1 || auxToS390xCCMask(b.Aux) != s390x.Equal {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, borrow)
+			b.Aux = s390xCCMaskToAux(s390x.Borrow)
+			return true
+		}
+		// match: (CGIJ {s390x.LessOrGreater} (NEG (Select0 (SUBE (MOVDconst [0]) (MOVDconst [0]) borrow))) [0])
+		// result: (BRC {s390x.Borrow} borrow)
+		for b.Controls[0].Op == OpS390XNEG {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpSelect0 {
+				break
+			}
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XSUBE {
+				break
+			}
+			borrow := v_0_0_0.Args[2]
+			v_0_0_0_0 := v_0_0_0.Args[0]
+			if v_0_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_0_1 := v_0_0_0.Args[1]
+			if v_0_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_1.AuxInt) != 0 || auxIntToInt8(b.AuxInt) != 0 || auxToS390xCCMask(b.Aux) != s390x.LessOrGreater {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, borrow)
+			b.Aux = s390xCCMaskToAux(s390x.Borrow)
+			return true
+		}
+		// match: (CGIJ {s390x.LessOrGreater} (NEG (Select0 (SUBE (MOVDconst [0]) (MOVDconst [0]) borrow))) [1])
+		// result: (BRC {s390x.NoBorrow} borrow)
+		for b.Controls[0].Op == OpS390XNEG {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpSelect0 {
+				break
+			}
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XSUBE {
+				break
+			}
+			borrow := v_0_0_0.Args[2]
+			v_0_0_0_0 := v_0_0_0.Args[0]
+			if v_0_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_0_1 := v_0_0_0.Args[1]
+			if v_0_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_1.AuxInt) != 0 || auxIntToInt8(b.AuxInt) != 1 || auxToS390xCCMask(b.Aux) != s390x.LessOrGreater {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, borrow)
+			b.Aux = s390xCCMaskToAux(s390x.NoBorrow)
+			return true
+		}
+		// match: (CGIJ {s390x.Greater} (NEG (Select0 (SUBE (MOVDconst [0]) (MOVDconst [0]) borrow))) [0])
+		// result: (BRC {s390x.Borrow} borrow)
+		for b.Controls[0].Op == OpS390XNEG {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpSelect0 {
+				break
+			}
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XSUBE {
+				break
+			}
+			borrow := v_0_0_0.Args[2]
+			v_0_0_0_0 := v_0_0_0.Args[0]
+			if v_0_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_0_1 := v_0_0_0.Args[1]
+			if v_0_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_1.AuxInt) != 0 || auxIntToInt8(b.AuxInt) != 0 || auxToS390xCCMask(b.Aux) != s390x.Greater {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, borrow)
+			b.Aux = s390xCCMaskToAux(s390x.Borrow)
+			return true
+		}
 	case BlockS390XCGRJ:
 		// match: (CGRJ {c} x (MOVDconst [y]) yes no)
 		// cond: is8Bit(y)
@@ -19993,6 +20223,236 @@ func rewriteBlockS390X(b *Block) bool {
 			b.swapSuccessors()
 			return true
 		}
+		// match: (CLGIJ {s390x.Equal} (Select0 (ADDE (MOVDconst [0]) (MOVDconst [0]) carry)) [0])
+		// result: (BRC {s390x.NoCarry} carry)
+		for b.Controls[0].Op == OpSelect0 {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpS390XADDE {
+				break
+			}
+			carry := v_0_0.Args[2]
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_1 := v_0_0.Args[1]
+			if v_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_1.AuxInt) != 0 || auxIntToUint8(b.AuxInt) != 0 || auxToS390xCCMask(b.Aux) != s390x.Equal {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, carry)
+			b.Aux = s390xCCMaskToAux(s390x.NoCarry)
+			return true
+		}
+		// match: (CLGIJ {s390x.Equal} (Select0 (ADDE (MOVDconst [0]) (MOVDconst [0]) carry)) [1])
+		// result: (BRC {s390x.Carry} carry)
+		for b.Controls[0].Op == OpSelect0 {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpS390XADDE {
+				break
+			}
+			carry := v_0_0.Args[2]
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_1 := v_0_0.Args[1]
+			if v_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_1.AuxInt) != 0 || auxIntToUint8(b.AuxInt) != 1 || auxToS390xCCMask(b.Aux) != s390x.Equal {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, carry)
+			b.Aux = s390xCCMaskToAux(s390x.Carry)
+			return true
+		}
+		// match: (CLGIJ {s390x.LessOrGreater} (Select0 (ADDE (MOVDconst [0]) (MOVDconst [0]) carry)) [0])
+		// result: (BRC {s390x.Carry} carry)
+		for b.Controls[0].Op == OpSelect0 {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpS390XADDE {
+				break
+			}
+			carry := v_0_0.Args[2]
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_1 := v_0_0.Args[1]
+			if v_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_1.AuxInt) != 0 || auxIntToUint8(b.AuxInt) != 0 || auxToS390xCCMask(b.Aux) != s390x.LessOrGreater {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, carry)
+			b.Aux = s390xCCMaskToAux(s390x.Carry)
+			return true
+		}
+		// match: (CLGIJ {s390x.LessOrGreater} (Select0 (ADDE (MOVDconst [0]) (MOVDconst [0]) carry)) [1])
+		// result: (BRC {s390x.NoCarry} carry)
+		for b.Controls[0].Op == OpSelect0 {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpS390XADDE {
+				break
+			}
+			carry := v_0_0.Args[2]
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_1 := v_0_0.Args[1]
+			if v_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_1.AuxInt) != 0 || auxIntToUint8(b.AuxInt) != 1 || auxToS390xCCMask(b.Aux) != s390x.LessOrGreater {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, carry)
+			b.Aux = s390xCCMaskToAux(s390x.NoCarry)
+			return true
+		}
+		// match: (CLGIJ {s390x.Greater} (Select0 (ADDE (MOVDconst [0]) (MOVDconst [0]) carry)) [0])
+		// result: (BRC {s390x.Carry} carry)
+		for b.Controls[0].Op == OpSelect0 {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpS390XADDE {
+				break
+			}
+			carry := v_0_0.Args[2]
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_1 := v_0_0.Args[1]
+			if v_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_1.AuxInt) != 0 || auxIntToUint8(b.AuxInt) != 0 || auxToS390xCCMask(b.Aux) != s390x.Greater {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, carry)
+			b.Aux = s390xCCMaskToAux(s390x.Carry)
+			return true
+		}
+		// match: (CLGIJ {s390x.Equal} (NEG (Select0 (SUBE (MOVDconst [0]) (MOVDconst [0]) borrow))) [0])
+		// result: (BRC {s390x.NoBorrow} borrow)
+		for b.Controls[0].Op == OpS390XNEG {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpSelect0 {
+				break
+			}
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XSUBE {
+				break
+			}
+			borrow := v_0_0_0.Args[2]
+			v_0_0_0_0 := v_0_0_0.Args[0]
+			if v_0_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_0_1 := v_0_0_0.Args[1]
+			if v_0_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_1.AuxInt) != 0 || auxIntToUint8(b.AuxInt) != 0 || auxToS390xCCMask(b.Aux) != s390x.Equal {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, borrow)
+			b.Aux = s390xCCMaskToAux(s390x.NoBorrow)
+			return true
+		}
+		// match: (CLGIJ {s390x.Equal} (NEG (Select0 (SUBE (MOVDconst [0]) (MOVDconst [0]) borrow))) [1])
+		// result: (BRC {s390x.Borrow} borrow)
+		for b.Controls[0].Op == OpS390XNEG {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpSelect0 {
+				break
+			}
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XSUBE {
+				break
+			}
+			borrow := v_0_0_0.Args[2]
+			v_0_0_0_0 := v_0_0_0.Args[0]
+			if v_0_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_0_1 := v_0_0_0.Args[1]
+			if v_0_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_1.AuxInt) != 0 || auxIntToUint8(b.AuxInt) != 1 || auxToS390xCCMask(b.Aux) != s390x.Equal {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, borrow)
+			b.Aux = s390xCCMaskToAux(s390x.Borrow)
+			return true
+		}
+		// match: (CLGIJ {s390x.LessOrGreater} (NEG (Select0 (SUBE (MOVDconst [0]) (MOVDconst [0]) borrow))) [0])
+		// result: (BRC {s390x.Borrow} borrow)
+		for b.Controls[0].Op == OpS390XNEG {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpSelect0 {
+				break
+			}
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XSUBE {
+				break
+			}
+			borrow := v_0_0_0.Args[2]
+			v_0_0_0_0 := v_0_0_0.Args[0]
+			if v_0_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_0_1 := v_0_0_0.Args[1]
+			if v_0_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_1.AuxInt) != 0 || auxIntToUint8(b.AuxInt) != 0 || auxToS390xCCMask(b.Aux) != s390x.LessOrGreater {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, borrow)
+			b.Aux = s390xCCMaskToAux(s390x.Borrow)
+			return true
+		}
+		// match: (CLGIJ {s390x.LessOrGreater} (NEG (Select0 (SUBE (MOVDconst [0]) (MOVDconst [0]) borrow))) [1])
+		// result: (BRC {s390x.NoBorrow} borrow)
+		for b.Controls[0].Op == OpS390XNEG {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpSelect0 {
+				break
+			}
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XSUBE {
+				break
+			}
+			borrow := v_0_0_0.Args[2]
+			v_0_0_0_0 := v_0_0_0.Args[0]
+			if v_0_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_0_1 := v_0_0_0.Args[1]
+			if v_0_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_1.AuxInt) != 0 || auxIntToUint8(b.AuxInt) != 1 || auxToS390xCCMask(b.Aux) != s390x.LessOrGreater {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, borrow)
+			b.Aux = s390xCCMaskToAux(s390x.NoBorrow)
+			return true
+		}
+		// match: (CLGIJ {s390x.Greater} (NEG (Select0 (SUBE (MOVDconst [0]) (MOVDconst [0]) borrow))) [0])
+		// result: (BRC {s390x.Borrow} borrow)
+		for b.Controls[0].Op == OpS390XNEG {
+			v_0 := b.Controls[0]
+			v_0_0 := v_0.Args[0]
+			if v_0_0.Op != OpSelect0 {
+				break
+			}
+			v_0_0_0 := v_0_0.Args[0]
+			if v_0_0_0.Op != OpS390XSUBE {
+				break
+			}
+			borrow := v_0_0_0.Args[2]
+			v_0_0_0_0 := v_0_0_0.Args[0]
+			if v_0_0_0_0.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_0.AuxInt) != 0 {
+				break
+			}
+			v_0_0_0_1 := v_0_0_0.Args[1]
+			if v_0_0_0_1.Op != OpS390XMOVDconst || auxIntToInt64(v_0_0_0_1.AuxInt) != 0 || auxIntToUint8(b.AuxInt) != 0 || auxToS390xCCMask(b.Aux) != s390x.Greater {
+				break
+			}
+			b.resetWithControl(BlockS390XBRC, borrow)
+			b.Aux = s390xCCMaskToAux(s390x.Borrow)
+			return true
+		}
 	case BlockS390XCLGRJ:
 		// match: (CLGRJ {c} x (MOVDconst [y]) yes no)
 		// cond: isU8Bit(y)
diff --git a/src/cmd/internal/obj/s390x/condition_code.go b/src/cmd/internal/obj/s390x/condition_code.go
index a112911a32..764fc5bc6a 100644
--- a/src/cmd/internal/obj/s390x/condition_code.go
+++ b/src/cmd/internal/obj/s390x/condition_code.go
@@ -50,6 +50,12 @@ const (
 
 	// 4-bit mask
 	Always CCMask = Equal | Less | Greater | Unordered
+
+	// useful aliases
+	Carry    CCMask = GreaterOrUnordered
+	NoCarry  CCMask = LessOrEqual
+	Borrow   CCMask = NoCarry
+	NoBorrow CCMask = Carry
 )
 
 // Inverse returns the complement of the condition code mask.
diff --git a/src/math/bits/bits_test.go b/src/math/bits/bits_test.go
index c0f43093d9..23b4539fcd 100644
--- a/src/math/bits/bits_test.go
+++ b/src/math/bits/bits_test.go
@@ -806,6 +806,130 @@ func TestAddSubUint64(t *testing.T) {
 	}
 }
 
+func TestAdd64OverflowPanic(t *testing.T) {
+	// Test that 64-bit overflow panics fire correctly.
+	// These are designed to improve coverage of compiler intrinsics.
+	tests := []func(uint64, uint64) uint64{
+		func(a, b uint64) uint64 {
+			x, c := Add64(a, b, 0)
+			if c > 0 {
+				panic("overflow")
+			}
+			return x
+		},
+		func(a, b uint64) uint64 {
+			x, c := Add64(a, b, 0)
+			if c != 0 {
+				panic("overflow")
+			}
+			return x
+		},
+		func(a, b uint64) uint64 {
+			x, c := Add64(a, b, 0)
+			if c == 1 {
+				panic("overflow")
+			}
+			return x
+		},
+		func(a, b uint64) uint64 {
+			x, c := Add64(a, b, 0)
+			if c != 1 {
+				return x
+			}
+			panic("overflow")
+		},
+		func(a, b uint64) uint64 {
+			x, c := Add64(a, b, 0)
+			if c == 0 {
+				return x
+			}
+			panic("overflow")
+		},
+	}
+	for _, test := range tests {
+		shouldPanic := func(f func()) {
+			defer func() {
+				if err := recover(); err == nil {
+					t.Fatalf("expected panic")
+				}
+			}()
+			f()
+		}
+
+		// overflow
+		shouldPanic(func() { test(_M64, 1) })
+		shouldPanic(func() { test(1, _M64) })
+		shouldPanic(func() { test(_M64, _M64) })
+
+		// no overflow
+		test(_M64, 0)
+		test(0, 0)
+		test(1, 1)
+	}
+}
+
+func TestSub64OverflowPanic(t *testing.T) {
+	// Test that 64-bit overflow panics fire correctly.
+	// These are designed to improve coverage of compiler intrinsics.
+	tests := []func(uint64, uint64) uint64{
+		func(a, b uint64) uint64 {
+			x, c := Sub64(a, b, 0)
+			if c > 0 {
+				panic("overflow")
+			}
+			return x
+		},
+		func(a, b uint64) uint64 {
+			x, c := Sub64(a, b, 0)
+			if c != 0 {
+				panic("overflow")
+			}
+			return x
+		},
+		func(a, b uint64) uint64 {
+			x, c := Sub64(a, b, 0)
+			if c == 1 {
+				panic("overflow")
+			}
+			return x
+		},
+		func(a, b uint64) uint64 {
+			x, c := Sub64(a, b, 0)
+			if c != 1 {
+				return x
+			}
+			panic("overflow")
+		},
+		func(a, b uint64) uint64 {
+			x, c := Sub64(a, b, 0)
+			if c == 0 {
+				return x
+			}
+			panic("overflow")
+		},
+	}
+	for _, test := range tests {
+		shouldPanic := func(f func()) {
+			defer func() {
+				if err := recover(); err == nil {
+					t.Fatalf("expected panic")
+				}
+			}()
+			f()
+		}
+
+		// overflow
+		shouldPanic(func() { test(0, 1) })
+		shouldPanic(func() { test(1, _M64) })
+		shouldPanic(func() { test(_M64-1, _M64) })
+
+		// no overflow
+		test(_M64, 0)
+		test(0, 0)
+		test(1, 1)
+	}
+}
+
 func TestMulDiv(t *testing.T) {
 	testMul := func(msg string, f func(x, y uint) (hi, lo uint), x, y, hi, lo uint) {
 		hi1, lo1 := f(x, y)