[llvm] Resolve fixme: create cld only when needed (PR #82415)
Craig Topper via llvm-commits
llvm-commits at lists.llvm.org
Tue Feb 20 14:16:44 PST 2024
================
@@ -2194,13 +2194,35 @@ void X86FrameLowering::emitPrologue(MachineFunction &MF,
// flag (DF in EFLAGS register). Clear this flag by creating "cld" instruction
// in each prologue of interrupt handler function.
//
- // FIXME: Create "cld" instruction only in these cases:
+ // Create "cld" instruction only in these cases:
// 1. The interrupt handling function uses any of the "rep" instructions.
// 2. Interrupt handling function calls another function.
//
- if (Fn.getCallingConv() == CallingConv::X86_INTR)
- BuildMI(MBB, MBBI, DL, TII.get(X86::CLD))
- .setMIFlag(MachineInstr::FrameSetup);
+ if (Fn.getCallingConv() == CallingConv::X86_INTR) {
+ bool NeedsCLD = false;
+
+ // Check if the function calls another function.
+ for (const BasicBlock &BB : Fn) {
+ for (const Instruction &I : BB) {
+ if (isa<CallInst>(I)) {
+ NeedsCLD = true;
+ break;
+ }
+
+ // Check for rep opcode.
+ unsigned Opcode = I.getOpcode();
+ if (Opcode == X86::REP_PREFIX || Opcode == X86::REPNE_PREFIX) {
----------------
topperc wrote:
I don't think these will ever appear as a MachineInstr. You need to check for REP_MOVSB_32 and friends from X86InstrCompiler.td. Those are pseudoinstructions that represent a repeated operation. We can't model them as separate instructions in MIR because the REP and MOVSB must be kept adjacent in the instruction stream.
https://github.com/llvm/llvm-project/pull/82415
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