From: "Paul A. Clarke" <p...@us.ibm.com> - target/ppc/fpu_helper.c: - helper_todouble() was not properly converting INFINITY from 32 bit float to 64 bit double. - helper_todouble() was not properly converting any denormalized 32 bit float to 64 bit double.
- GCC, as of version 8 or so, takes advantage of the hardware's implementation of the xscvdpspn instruction to optimize the following sequence: xscvdpspn vs0,vs1 mffprwz r8,f0 ISA 3.0B has xscvdpspn leaving its result in word 1 of the target register, and mffprwz expecting its input to come from word 0 of the source register. This sequence fails with QEMU, as a shift is required between those two instructions. However, the hardware splats the result to both word 0 and word 1 of its output register, so the shift is not necessary. Expect a future revision of the ISA to specify this behavior. Signed-off-by: Paul A. Clarke <p...@us.ibm.com> --- target/ppc/fpu_helper.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/target/ppc/fpu_helper.c b/target/ppc/fpu_helper.c index 5611cf0..82b5425 100644 --- a/target/ppc/fpu_helper.c +++ b/target/ppc/fpu_helper.c @@ -62,13 +62,14 @@ uint64_t helper_todouble(uint32_t arg) ret = (uint64_t)extract32(arg, 30, 2) << 62; ret |= ((extract32(arg, 30, 1) ^ 1) * (uint64_t)7) << 59; ret |= (uint64_t)extract32(arg, 0, 30) << 29; + ret |= (0x7ffULL * (extract32(arg, 23, 8) == 0xff)) << 52; } else { /* Zero or Denormalized operand. */ ret = (uint64_t)extract32(arg, 31, 1) << 63; if (unlikely(abs_arg != 0)) { /* Denormalized operand. */ int shift = clz32(abs_arg) - 9; - int exp = -126 - shift + 1023; + int exp = -127 - shift + 1023; ret |= (uint64_t)exp << 52; ret |= abs_arg << (shift + 29); } @@ -2871,10 +2872,14 @@ void helper_xscvqpdp(CPUPPCState *env, uint32_t opcode, uint64_t helper_xscvdpspn(CPUPPCState *env, uint64_t xb) { + uint64_t result; + float_status tstat = env->fp_status; set_float_exception_flags(0, &tstat); - return (uint64_t)float64_to_float32(xb, &tstat) << 32; + result = (uint64_t)float64_to_float32(xb, &tstat); + /* hardware replicates result to both words of the doubleword result. */ + return (result << 32) | result; } uint64_t helper_xscvspdpn(CPUPPCState *env, uint64_t xb) -- 1.8.3.1