The _m64 type is represented in IR as <1 x i64>. The x86-64 ABI
on Linux passes <1 x i64> as a double. MMX intrinsics use x86_mmx
type in IR.These things result in a lot of bitcasts in mmx code.
There's another instcombine that tries to turn bitcast <1 x i64>
to double into extractelement and a bitcast.
The combine here tries to reverse this extractelement conversion
if we see an mmx type.
Worklist.AddValue(EE);
return CastInst::Create(CI->getOpcode(), EE, EI.getType());
}
+
+ // If the input is a bitcast from x86_mmx, turn into a single bitcast from
+ // the mmx type to the scalar type.
+ if (CI->getOpcode() == Instruction::BitCast &&
+ EI.getVectorOperandType()->getNumElements() == 1 &&
+ CI->getOperand(0)->getType()->isX86_MMXTy())
+ return new BitCastInst(CI->getOperand(0), EI.getType());
}
}
return nullptr;
define double @g(x86_mmx %x) {
; CHECK-LABEL: @g(
; CHECK-NEXT: entry:
-; CHECK-NEXT: [[BC:%.*]] = bitcast x86_mmx %x to <1 x double>
-; CHECK-NEXT: [[TMP0:%.*]] = extractelement <1 x double> [[BC]], i32 0
+; CHECK-NEXT: [[TMP0:%.*]] = bitcast x86_mmx [[X:%.*]] to double
; CHECK-NEXT: ret double [[TMP0]]
;
entry: