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compiler(amd64): avoid unnecessary jump in signed remainder (#1514)

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Signed-off-by: Nuno Cruces <ncruces@users.noreply.github.com>
This commit is contained in:
Nuno Cruces
2023-06-13 01:01:34 +01:00
committed by GitHub
parent f3778cae08
commit e3755ce4af
1 changed files with 6 additions and 18 deletions
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24
internal/engine/compiler/impl_amd64.go
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@@ -1549,29 +1549,17 @@ func (c *amd64Compiler) performDivisionOnInts(isRem, is32Bit, signed bool) error
// for divisions on (-2^31) / -1 where we do not need to emit the special branches.
// For detail, please refer to https://stackoverflow.com/questions/56303282/why-idiv-with-1-causes-floating-point-exception
// First we compare the division with -1.
// First we store zero into the remainder result register (DX) and compare the divisor with -1.
if is32Bit {
c.assembler.CompileRegisterToRegister(amd64.XORL, remainderRegister, remainderRegister)
c.assembler.CompileRegisterToConst(amd64.CMPL, x2.register, -1)
} else {
c.assembler.CompileRegisterToRegister(amd64.XORQ, remainderRegister, remainderRegister)
c.assembler.CompileRegisterToConst(amd64.CMPQ, x2.register, -1)
}
// If it doesn't equal minus one, we jump to the normal case.
okJmp := c.assembler.CompileJump(amd64.JNE)
// Otherwise, we store zero into the remainder result register (DX).
if is32Bit {
c.assembler.CompileRegisterToRegister(amd64.XORL, remainderRegister, remainderRegister)
} else {
c.assembler.CompileRegisterToRegister(amd64.XORQ, remainderRegister, remainderRegister)
}
// Emit the exit jump instruction for the divisor -1 case so
// we skips the normal case.
signedRemMinusOneDivisorJmp = c.assembler.CompileJump(amd64.JMP)
// Set the normal case's jump target.
c.assembler.SetJumpTargetOnNext(okJmp)
// If it equals minus one, we skip the normal case.
signedRemMinusOneDivisorJmp = c.assembler.CompileJump(amd64.JEQ)
} else if isSignedDiv {
// For signed division, we have to have branches for "math.MinInt{32,64} / -1"
// case which results in the floating point exception via division error as
@@ -3999,7 +3987,7 @@ func (c *amd64Compiler) compileFillImpl(isTable bool, tableIndex uint32) error {
// destinationOffset += memory buffer's absolute address.
c.assembler.CompileRegisterToRegister(amd64.ADDQ, amd64ReservedRegisterForMemory, destinationOffset.register)
// Copy first %15 bytes with simple MOVB instruction.
// Copy first % 16 bytes with simple MOVB instruction.
beginCopyLoop := c.assembler.CompileStandAlone(amd64.NOP)
c.assembler.CompileConstToRegister(amd64.TESTQ, 15, copySize.register)
breakLoop := c.assembler.CompileJump(amd64.JEQ)