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[ARM] Rewrite .save/.vsave emission with bit math

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Hopefully makes it a bit easier to understand what's going on.
No functional change intended.

llvm-svn: 233191
This commit is contained in:
Benjamin Kramer 2015-03-25 15:27:58 +00:00
parent 05bbd7484f
commit 6c5bd093e6
1 changed files with 20 additions and 50 deletions
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70
lib/Target/ARM/MCTargetDesc/ARMUnwindOpAsm.cpp
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@ -72,14 +72,10 @@ void UnwindOpcodeAssembler::EmitRegSave(uint32_t RegSave) {
// opcode when r4 is not in .save directive.
// Compute the consecutive registers from r4 to r11.
uint32_t Range = 0;
uint32_t Mask = (1u << 4);
for (uint32_t Bit = (1u << 5); Bit < (1u << 12); Bit <<= 1) {
if ((RegSave & Bit) == 0u)
break;
++Range;
Mask |= Bit;
}
uint32_t Mask = RegSave & 0xff0u;
uint32_t Range = countTrailingOnes(Mask >> 5); // Exclude r4.
// Mask off non-consecutive registers. Keep r4.
Mask &= ~(0xffffffe0u << Range);
// Emit this opcode when the mask covers every registers.
uint32_t UnmaskedReg = RegSave & 0xfff0u & (~Mask);
@ -105,50 +101,24 @@ void UnwindOpcodeAssembler::EmitRegSave(uint32_t RegSave) {
/// Emit unwind opcodes for .vsave directives
void UnwindOpcodeAssembler::EmitVFPRegSave(uint32_t VFPRegSave) {
size_t i = 32;
// We only have 4 bits to save the offset in the opcode so look at the lower
// and upper 16 bits separately.
for (uint32_t Regs : {VFPRegSave & 0xffff0000u, VFPRegSave & 0x0000ffffu}) {
while (Regs) {
// Now look for a run of set bits. Remember the MSB and LSB of the run.
auto RangeMSB = 32 - countLeadingZeros(Regs);
auto RangeLen = countLeadingOnes(Regs << (32 - RangeMSB));
auto RangeLSB = RangeMSB - RangeLen;
while (i > 16) {
uint32_t Bit = 1u << (i - 1);
if ((VFPRegSave & Bit) == 0u) {
--i;
continue;
int Opcode = RangeLSB >= 16
? ARM::EHABI::UNWIND_OPCODE_POP_VFP_REG_RANGE_FSTMFDD_D16
: ARM::EHABI::UNWIND_OPCODE_POP_VFP_REG_RANGE_FSTMFDD;
EmitInt16(Opcode | ((RangeLSB % 16) << 4) | (RangeLen - 1));
// Zero out bits we're done with.
Regs &= ~(-1u << RangeLSB);
}
uint32_t Range = 0;
--i;
Bit >>= 1;
while (i > 16 && (VFPRegSave & Bit)) {
--i;
++Range;
Bit >>= 1;
}
EmitInt16(ARM::EHABI::UNWIND_OPCODE_POP_VFP_REG_RANGE_FSTMFDD_D16 |
((i - 16) << 4) | Range);
}
while (i > 0) {
uint32_t Bit = 1u << (i - 1);
if ((VFPRegSave & Bit) == 0u) {
--i;
continue;
}
uint32_t Range = 0;
--i;
Bit >>= 1;
while (i > 0 && (VFPRegSave & Bit)) {
--i;
++Range;
Bit >>= 1;
}
EmitInt16(ARM::EHABI::UNWIND_OPCODE_POP_VFP_REG_RANGE_FSTMFDD | (i << 4) |
Range);
}
}