[release-branch.go1.5] cmd/asm: handle CMPF and CMPD on ARM

These instructions are special cases that were missed in the translation.
The second argument must go into the Reg field not the To field.

Fixes #12458

For Go 1.5.1

Change-Id: Iad57c60c7e38e3bcfafda483ed5037ce670e8816
Reviewed-on: https://go-review.googlesource.com/14183Reviewed-by: Dave Cheney <dave@cheney.net>
Reviewed-by: Russ Cox <rsc@golang.org>
Reviewed-on: https://go-review.googlesource.com/14358Reviewed-by: Chris Broadfoot <cbro@golang.org>
Reviewed-by: Rob Pike <r@golang.org>

src/cmd/asm/internal/arch/arm.go

@@ -121,6 +121,15 @@ func IsARMMRC(op int) bool {
 	return false
 }
 
+// IsARMFloatCmp reports whether the op is a floating comparison instruction.
+func IsARMFloatCmp(op int) bool {
+	switch op {
+	case arm.ACMPF, arm.ACMPD:
+		return true
+	}
+	return false
+}
+
 // ARMMRCOffset implements the peculiar encoding of the MRC and MCR instructions.
 // The difference between MRC and MCR is represented by a bit high in the word, not
 // in the usual way by the opcode itself. Asm must use AMRC for both instructions, so

src/cmd/asm/internal/asm/asm.go

@@ -463,6 +463,11 @@ func (p *Parser) asmInstruction(op int, cond string, a []obj.Addr) {
 				}
 				p.errorf("unrecognized addressing for %s", obj.Aconv(op))
 			}
+			if arch.IsARMFloatCmp(op) {
+				prog.From = a[0]
+				prog.Reg = p.getRegister(prog, op, &a[1])
+				break
+			}
 		} else if p.arch.Thechar == '7' && arch.IsARM64CMP(op) {
 			prog.From = a[0]
 			prog.Reg = p.getRegister(prog, op, &a[1])

src/cmd/asm/internal/asm/testdata/arm.out

@@ -56,4 +56,6 @@
 281 00056 (testdata/arm.s:281)	CALL	foo(SB)
 282 00057 (testdata/arm.s:282)	JMP	foo(SB)
 283 00058 (testdata/arm.s:283)	CALL	foo(SB)
-292 00059 (testdata/arm.s:292)	END
+286 00059 (testdata/arm.s:286)	CMPF	F1, F2
+287 00060 (testdata/arm.s:287)	CMPD	F1, F2
+296 00061 (testdata/arm.s:296)	END

src/cmd/asm/internal/asm/testdata/arm.s

@@ -282,6 +282,10 @@ TEXT	foo(SB), 0, $0
 	JMP	foo(SB)
 	CALL	foo(SB)
 
+// CMPF and CMPD are special.
+	CMPF F1, F2
+	CMPD F1, F2
+
 //
 // END
 //