cmd/internal/obj/arm64: fix BITCON constant printing error

For some 32-bit instructions whose first operand is a constant, we
copy the lower 32 bits of the constant into the upper 32 bits in progedit,
which leads to the wrong value being printed in -S output.

The purpose of this is that we don't need to distinguish between 32-bit
and 64-bit constants when checking C_BITCON, this CL puts the modified
value in a temporary variable, so that the constant operand of the
instruction will not be modified.

Fixes #53551

Change-Id: I40ee9223b4187bff1c0a1bab7eb508fcb30325f9
Reviewed-on: https://go-review.googlesource.com/c/go/+/414374
Run-TryBot: Eric Fang <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Keith Randall <[email protected]>

Author: eric fang

src/cmd/internal/obj/arm64/asm7.go

@@ -1557,6 +1557,10 @@ func sequenceOfOnes(x uint64) bool {
 // N=0, S=11110x -- period=2
 // R is the shift amount, low bits of S = n-1
 func bitconEncode(x uint64, mode int) uint32 {
+	if mode == 32 {
+		x &= 0xffffffff
+		x = x<<32 | x
+	}
 	var period uint32
 	// determine the period and sign-extend a unit to 64 bits
 	switch {
@@ -1825,17 +1829,24 @@ func rclass(r int16) int {
 // but saved in Offset which type is int64, con32class treats it as uint32 type and reclassifies it.
 func (c *ctxt7) con32class(a *obj.Addr) int {
 	v := uint32(a.Offset)
+	// For 32-bit instruction with constant, rewrite
+	// the high 32-bit to be a repetition of the low
+	// 32-bit, so that the BITCON test can be shared
+	// for both 32-bit and 64-bit. 32-bit ops will
+	// zero the high 32-bit of the destination register
+	// anyway.
+	vbitcon := uint64(v)<<32 | uint64(v)
 	if v == 0 {
 		return C_ZCON
 	}
 	if isaddcon(int64(v)) {
 		if v <= 0xFFF {
-			if isbitcon(uint64(a.Offset)) {
+			if isbitcon(vbitcon) {
 				return C_ABCON0
 			}
 			return C_ADDCON0
 		}
-		if isbitcon(uint64(a.Offset)) {
+		if isbitcon(vbitcon) {
 			return C_ABCON
 		}
 		if movcon(int64(v)) >= 0 {
@@ -1849,21 +1860,21 @@ func (c *ctxt7) con32class(a *obj.Addr) int {
 
 	t := movcon(int64(v))
 	if t >= 0 {
-		if isbitcon(uint64(a.Offset)) {
+		if isbitcon(vbitcon) {
 			return C_MBCON
 		}
 		return C_MOVCON
 	}
 
 	t = movcon(int64(^v))
 	if t >= 0 {
-		if isbitcon(uint64(a.Offset)) {
+		if isbitcon(vbitcon) {
 			return C_MBCON
 		}
 		return C_MOVCON
 	}
 
-	if isbitcon(uint64(a.Offset)) {
+	if isbitcon(vbitcon) {
 		return C_BITCON
 	}
 

src/cmd/internal/obj/arm64/obj7.go

@@ -382,19 +382,6 @@ func progedit(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc) {
 		}
 	}
 
-	// For 32-bit instruction with constant, rewrite
-	// the high 32-bit to be a repetition of the low
-	// 32-bit, so that the BITCON test can be shared
-	// for both 32-bit and 64-bit. 32-bit ops will
-	// zero the high 32-bit of the destination register
-	// anyway.
-	// For MOVW, the destination register can't be ZR,
-	// so don't bother rewriting it in this situation.
-	if (isANDWop(p.As) || isADDWop(p.As) || p.As == AMOVW && p.To.Reg != REGZERO) && p.From.Type == obj.TYPE_CONST {
-		v := p.From.Offset & 0xffffffff
-		p.From.Offset = v | v<<32
-	}
-
 	if c.ctxt.Flag_dynlink {
 		c.rewriteToUseGot(p)
 	}