[LLVMdev] compiler-rt's arm vfp o<= implementation

Nick Lewycky nlewycky at google.com
Wed Apr 7 22:50:56 PDT 2010

The implementation of an float ordered <= looks buggy, but maybe I'm not
reading the assembly right. This is lesf2vfp.S in compiler-rt, and it has
this code:

// extern int __lesf2vfp(float a, float b);
// Returns one iff a <= b and neither is NaN.
// Uses Darwin calling convention where single precision arguments are passsed
// like 32-bit ints
	fmsr	s14, r0     // move from GPR 0 to float register
	fmsr	s15, r1     // move from GPR 1 to float register
	fcmps	s14, s15
	movls	r0, #1      // set result register to 1 if equal
	movhi	r0, #0
	bx	lr

If I read this right, the high bits of r0 are always cleared (by the movhi)
while the low bits are conditionally set to 1 (by the movls), but there's
nothing to clear the r0's low bits in the false case. Is this a bug or have
I misunderstood the assembly?

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