[X86] Connect the default fpsr and dirflag clobbers in inline assembly to the registers we have defined for them.

[craig.topper]

Summary

We don't currently map these constraints to physical register numbers so they don't make it to the MachineIR representation of inline assembly.

This could have problems for proper dependency tracking in the machine schedulers though I don't have a test case that shows that.

[rnk]

lgtm

lib/Target/X86/X86ISelLowering.cpp

42961

Comment is stale.

[craig.topper]

Fix stale comment

lib/Target/X86/X86ISelLowering.cpp

       if (!Subtarget.hasMMX()) break;
       return std::make_pair(0U, &X86::VR64RegClass);
     case 'z':
     case '0':
       if (!Subtarget.hasSSE1()) break;
       return std::make_pair(X86::XMM0, &X86::VR128RegClass);
     case 'k':
       // This register class doesn't allocate k0 for masked vector operation.
       if (Subtarget.hasAVX512()) { // Only supported in AVX512.
         switch (VT.SimpleTy) {
         default: break;
         case MVT::i32:
           return std::make_pair(0U, &X86::VK32WMRegClass);
         case MVT::i16:
           return std::make_pair(0U, &X86::VK16WMRegClass);
         case MVT::i8:
           return std::make_pair(0U, &X86::VK8WMRegClass);

     // GCC allows "st(0)" to be called just plain "st".
     if (StringRef("{st}").equals_lower(Constraint))
       return std::make_pair(X86::FP0, &X86::RFP80RegClass);
 
     // flags -> EFLAGS
     if (StringRef("{flags}").equals_lower(Constraint))
       return std::make_pair(X86::EFLAGS, &X86::CCRRegClass);
 
+    // dirflag -> DF
+    if (StringRef("{dirflag}").equals_lower(Constraint))
+      return std::make_pair(X86::DF, &X86::DFCCRRegClass);
+
+    // fpsr -> FPSW
+    if (StringRef("{fpsr}").equals_lower(Constraint))
+      return std::make_pair(X86::FPSW, &X86::FPCCRRegClass);
+
     // 'A' means [ER]AX + [ER]DX.
     if (Constraint == "A") {
       if (Subtarget.is64Bit())
         return std::make_pair(X86::RAX, &X86::GR64_ADRegClass);
       assert((Subtarget.is32Bit() || Subtarget.is16Bit()) &&
              "Expecting 64, 32 or 16 bit subtarget");
       return std::make_pair(X86::EAX, &X86::GR32_ADRegClass);
     }

lib/Target/X86/X86RegisterInfo.td

 def ST2 : X86Reg<"st(2)", 2>, DwarfRegNum<[35, 14, 13]>;
 def ST3 : X86Reg<"st(3)", 3>, DwarfRegNum<[36, 15, 14]>;
 def ST4 : X86Reg<"st(4)", 4>, DwarfRegNum<[37, 16, 15]>;
 def ST5 : X86Reg<"st(5)", 5>, DwarfRegNum<[38, 17, 16]>;
 def ST6 : X86Reg<"st(6)", 6>, DwarfRegNum<[39, 18, 17]>;
 def ST7 : X86Reg<"st(7)", 7>, DwarfRegNum<[40, 19, 18]>;
 
 // Floating-point status word
-def FPSW : X86Reg<"fpsw", 0>;
+def FPSW : X86Reg<"fpsr", 0>;
 
 // Status flags register.
 //
 // Note that some flags that are commonly thought of as part of the status
 // flags register are modeled separately. Typically this is due to instructions
 // reading and updating those flags independently of all the others. We don't
 // want to create false dependencies between these instructions and so we use
 // a separate register to model them.

test/CodeGen/X86/inline-asm-default-clobbers.ll

+; RUN: llc < %s -mtriple=i686 -stop-after=expand-isel-pseudos | FileCheck %s
+
+; CHECK: INLINEASM &"", 1, 12, implicit-def early-clobber $df, 12, implicit-def early-clobber $fpsw, 12, implicit-def early-clobber $eflags
+define void @foo() {
+entry:
+  call void asm sideeffect "", "~{dirflag},~{fpsr},~{flags}"()
+  ret void
+}