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LLVM: lower float negation with xor a constant

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Rather than a compiler-rt call in the case that LLVM does not support
lowering the fneg instruction.
This commit is contained in:
Andrew Kelley
2022-06-30 11:48:37 -07:00
parent c8531faaf5
commit b3b96b5e28
1 changed files with 10 additions and 4 deletions
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14
src/codegen/llvm.zig
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@@ -6598,10 +6598,16 @@ pub const FuncGen = struct {
} else b: {
const float_bits = scalar_ty.floatBits(target);
break :b switch (op) {
.neg => FloatOpStrat{
.libc = std.fmt.bufPrintZ(&fn_name_buf, "__neg{s}f2", .{
compilerRtFloatAbbrev(float_bits),
}) catch unreachable,
.neg => {
// In this case we can generate a softfloat negation by XORing the
// bits with a constant.
const int_llvm_ty = self.dg.context.intType(float_bits);
const one = int_llvm_ty.constInt(1, .False);
const shift_amt = int_llvm_ty.constInt(float_bits - 1, .False);
const sign_mask = one.constShl(shift_amt);
const bitcasted_operand = self.builder.buildBitCast(params[0], int_llvm_ty, "");
const result = self.builder.buildXor(bitcasted_operand, sign_mask, "");
return self.builder.buildBitCast(result, llvm_ty, "");
},
.add, .sub, .div, .mul => FloatOpStrat{
.libc = std.fmt.bufPrintZ(&fn_name_buf, "__{s}{s}f3", .{