cmd/compile: make panicBounds stack frame smaller on ppc64

We're running into nosplit limits when compiled with all=-N -l.

Fixes #74910

Change-Id: I156263ae9b54ded240000001719512af86af70ee
Reviewed-on: https://go-review.googlesource.com/c/go/+/693557
Reviewed-by: Paul Murphy <[email protected]>
Auto-Submit: Keith Randall <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Keith Randall <[email protected]>

Author: randall77

src/cmd/compile/internal/ssa/_gen/PPC64Ops.go

@@ -171,7 +171,7 @@ func init() {
 		fpstore     = regInfo{inputs: []regMask{gp | sp | sb, fp}}
 		fpstoreidx  = regInfo{inputs: []regMask{gp | sp | sb, gp | sp | sb, fp}}
 		callerSave  = regMask(gp | fp | gr | xer)
-		first8      = buildReg("R3 R4 R5 R6 R7 R8 R9 R10")
+		first7      = buildReg("R3 R4 R5 R6 R7 R8 R9")
 	)
 	ops := []opData{
 		{name: "ADD", argLength: 2, reg: gp21, asm: "ADD", commutative: true},                              // arg0 + arg1
@@ -709,9 +709,9 @@ func init() {
 		// when both are constant (normally both 0, as prove derives the fact that a [0] bounds
 		// failure means the length must have also been 0).
 		// AuxInt contains a report code (see PanicBounds in genericOps.go).
-		{name: "LoweredPanicBoundsRR", argLength: 3, aux: "Int64", reg: regInfo{inputs: []regMask{first8, first8}}, typ: "Mem", call: true}, // arg0=x, arg1=y, arg2=mem, returns memory.
-		{name: "LoweredPanicBoundsRC", argLength: 2, aux: "PanicBoundsC", reg: regInfo{inputs: []regMask{first8}}, typ: "Mem", call: true},  // arg0=x, arg1=mem, returns memory.
-		{name: "LoweredPanicBoundsCR", argLength: 2, aux: "PanicBoundsC", reg: regInfo{inputs: []regMask{first8}}, typ: "Mem", call: true},  // arg0=y, arg1=mem, returns memory.
+		{name: "LoweredPanicBoundsRR", argLength: 3, aux: "Int64", reg: regInfo{inputs: []regMask{first7, first7}}, typ: "Mem", call: true}, // arg0=x, arg1=y, arg2=mem, returns memory.
+		{name: "LoweredPanicBoundsRC", argLength: 2, aux: "PanicBoundsC", reg: regInfo{inputs: []regMask{first7}}, typ: "Mem", call: true},  // arg0=x, arg1=mem, returns memory.
+		{name: "LoweredPanicBoundsCR", argLength: 2, aux: "PanicBoundsC", reg: regInfo{inputs: []regMask{first7}}, typ: "Mem", call: true},  // arg0=y, arg1=mem, returns memory.
 		{name: "LoweredPanicBoundsCC", argLength: 1, aux: "PanicBoundsCC", reg: regInfo{}, typ: "Mem", call: true},                          // arg0=mem, returns memory.
 
 		// (InvertFlags (CMP a b)) == (CMP b a)

src/cmd/compile/internal/ssa/opGen.go

@@ -1350,13 +1350,13 @@ TEXT runtime·debugCallPanicked(SB),NOSPLIT,$32-16
 	RET
 #endif
 
-TEXT runtime·panicBounds<ABIInternal>(SB),NOSPLIT,$104-0
+TEXT runtime·panicBounds<ABIInternal>(SB),NOSPLIT,$88-0
 	// Note: frame size is 16 bytes larger than necessary
 	// in order to pacify vet. Vet doesn't understand ppc64
 	// layout properly.
 	NO_LOCAL_POINTERS
-	// Save all 8 int registers that could have an index in them.
-	// They may be pointers, but if they are they are dead.
+	// Save all 7 int registers that could have an index in them.
+	// They may be pointers, but if so they are dead.
 	// Skip R0 aka ZERO, R1 aka SP, R2 aka SB
 	MOVD	R3, 48(R1)
 	MOVD	R4, 56(R1)
@@ -1365,8 +1365,7 @@ TEXT runtime·panicBounds<ABIInternal>(SB),NOSPLIT,$104-0
 	MOVD	R7, 80(R1)
 	MOVD	R8, 88(R1)
 	MOVD	R9, 96(R1)
-	MOVD	R10, 104(R1)
-	// Note: we only save 8 reigsters to keep under nosplit stack limit
+	// Note: we only save 7 registers to keep under nosplit stack limit
 	// Also, R11 is clobbered in dynamic linking situations
 
 	MOVD	LR, R3		// PC immediately after call to panicBounds