+// Return true for any instruction the copies the high bits of the first source
+// operand into the unused high bits of the destination operand.
+static bool hasUndefRegUpdate(unsigned Opcode) {
+ switch (Opcode) {
+ case X86::VCVTSI2SSrr:
+ case X86::Int_VCVTSI2SSrr:
+ case X86::VCVTSI2SS64rr:
+ case X86::Int_VCVTSI2SS64rr:
+ case X86::VCVTSI2SDrr:
+ case X86::Int_VCVTSI2SDrr:
+ case X86::VCVTSI2SD64rr:
+ case X86::Int_VCVTSI2SD64rr:
+ case X86::VCVTSD2SSrr:
+ case X86::Int_VCVTSD2SSrr:
+ case X86::VCVTSS2SDrr:
+ case X86::Int_VCVTSS2SDrr:
+ case X86::VRCPSSr:
+ case X86::VROUNDSDr:
+ case X86::VROUNDSDr_Int:
+ case X86::VROUNDSSr:
+ case X86::VROUNDSSr_Int:
+ case X86::VRSQRTSSr:
+ case X86::VSQRTSSr:
+
+ // AVX-512
+ case X86::VCVTSD2SSZrr:
+ case X86::VCVTSS2SDZrr:
+ return true;
+ }
+
+ return false;
+}
+
+/// Inform the ExeDepsFix pass how many idle instructions we would like before
+/// certain undef register reads.
+///
+/// This catches the VCVTSI2SD family of instructions:
+///
+/// vcvtsi2sdq %rax, %xmm0<undef>, %xmm14
+///
+/// We should to be careful *not* to catch VXOR idioms which are presumably
+/// handled specially in the pipeline:
+///
+/// vxorps %xmm1<undef>, %xmm1<undef>, %xmm1
+///
+/// Like getPartialRegUpdateClearance, this makes a strong assumption that the
+/// high bits that are passed-through are not live.
+unsigned X86InstrInfo::
+getUndefRegClearance(const MachineInstr *MI, unsigned &OpNum,
+ const TargetRegisterInfo *TRI) const {
+ if (!hasUndefRegUpdate(MI->getOpcode()))
+ return 0;
+
+ // Set the OpNum parameter to the first source operand.
+ OpNum = 1;
+
+ const MachineOperand &MO = MI->getOperand(OpNum);
+ if (MO.isUndef() && TargetRegisterInfo::isPhysicalRegister(MO.getReg())) {
+ // Use the same magic number as getPartialRegUpdateClearance.
+ return 16;
+ }
+ return 0;
+}
+