Don't emit st(0)/st(1) copies as FpMOV instructions. Use FpSET_ST? instead.

Based on a patch by Rafael Espíndola.

Attempt to make the FpSET_ST1 hack more robust, but we are still relying on
FpSET_ST0 preceeding it. This is only for supporting really weird x87 inline
asm.

We support:

  FpSET_ST0
  INLINEASM

  FpSET_ST0
  FpSET_ST1
  INLINEASM

with and without kills on the arguments. We don't support:

  FpSET_ST1
  FpSET_ST0
  INLINEASM

nor

  FpSET_ST1
  INLINEASM

Just Don't Do It!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108047 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 28 insertions, 40 deletions

diff --git a/lib/Target/X86/X86FloatingPoint.cpp b/lib/Target/X86/X86FloatingPoint.cpp
index bf60c882dd..cee4ad7020 100644
--- a/lib/Target/X86/X86FloatingPoint.cpp
+++ b/lib/Target/X86/X86FloatingPoint.cpp
@@ -1006,15 +1006,17 @@ void FPS::handleSpecialFP(MachineBasicBlock::iterator &I) {
   case X86::FpSET_ST0_32:
   case X86::FpSET_ST0_64:
   case X86::FpSET_ST0_80: {
+    // FpSET_ST0_80 is generated by copyRegToReg for setting up inline asm
+    // arguments that use an st constraint. We expect a sequence of
+    // instructions: Fp_SET_ST0 Fp_SET_ST1? INLINEASM
     unsigned Op0 = getFPReg(MI->getOperand(0));
 
-    // FpSET_ST0_80 is generated by copyRegToReg for both function return
-    // and inline assembly with the "st" constrain. In the latter case,
-    // it is possible for ST(0) to be alive after this instruction.
     if (!MI->killsRegister(X86::FP0 + Op0)) {
-      // Duplicate Op0
-      duplicateToTop(0, 7 /*temp register*/, I);
+      // Duplicate Op0 into a temporary on the stack top.
+      // This actually assumes that FP7 is dead.
+      duplicateToTop(Op0, 7, I);
     } else {
+      // Op0 is killed, so just swap it into position.
       moveToTop(Op0, I);
     }
     --StackTop;   // "Forget" we have something on the top of stack!
@@ -1022,17 +1024,29 @@ void FPS::handleSpecialFP(MachineBasicBlock::iterator &I) {
   }
   case X86::FpSET_ST1_32:
   case X86::FpSET_ST1_64:
-  case X86::FpSET_ST1_80:
-    // StackTop can be 1 if a FpSET_ST0_* was before this. Exchange them.
-    if (StackTop == 1) {
-      BuildMI(*MBB, I, dl, TII->get(X86::XCH_F)).addReg(X86::ST1);
-      ++NumFXCH;
-      StackTop = 0;
-      break;
+  case X86::FpSET_ST1_80: {
+    // Set up st(1) for inline asm. We are assuming that st(0) has already been
+    // set up by FpSET_ST0, and our StackTop is off by one because of it.
+    unsigned Op0 = getFPReg(MI->getOperand(0));
+    // Restore the actual StackTop from before Fp_SET_ST0.
+    // Note we can't handle Fp_SET_ST1 without a preceeding Fp_SET_ST0, and we
+    // are not enforcing the constraint.
+    ++StackTop;
+    unsigned RegOnTop = getStackEntry(0); // This reg must remain in st(0).
+    if (!MI->killsRegister(X86::FP0 + Op0)) {
+      // Assume FP6 is not live, use it as a scratch register.
+      duplicateToTop(Op0, 6, I);
+      moveToTop(RegOnTop, I);
+    } else if (getSTReg(Op0) != X86::ST1) {
+      // We have the wrong value at st(1). Shuffle! Untested!
+      moveToTop(getStackEntry(1), I);
+      moveToTop(Op0, I);
+      moveToTop(RegOnTop, I);
     }
-    assert(StackTop == 2 && "Stack should have two element on it to return!");
-    --StackTop;   // "Forget" we have something on the top of stack!
+    assert(StackTop >= 2 && "Too few live registers");
+    StackTop -= 2; // "Forget" both st(0) and st(1).
     break;
+  }
   case X86::MOV_Fp3232:
   case X86::MOV_Fp3264:
   case X86::MOV_Fp6432:
@@ -1046,32 +1060,6 @@ void FPS::handleSpecialFP(MachineBasicBlock::iterator &I) {
     unsigned SrcReg = getFPReg(MO1);
 
     const MachineOperand &MO0 = MI->getOperand(0);
-    // These can be created due to inline asm. Two address pass can introduce
-    // copies from RFP registers to virtual registers.
-    if (MO0.getReg() == X86::ST0 && SrcReg == 0) {
-      assert(MO1.isKill());
-      // Treat %ST0<def> = MOV_Fp8080 %FP0<kill>
-      // like  FpSET_ST0_80 %FP0<kill>, %ST0<imp-def>
-      assert((StackTop == 1 || StackTop == 2)
-             && "Stack should have one or two element on it to return!");
-      --StackTop;   // "Forget" we have something on the top of stack!
-      break;
-    } else if (MO0.getReg() == X86::ST1 && SrcReg == 1) {
-      assert(MO1.isKill());
-      // Treat %ST1<def> = MOV_Fp8080 %FP1<kill>
-      // like  FpSET_ST1_80 %FP0<kill>, %ST1<imp-def>
-      // StackTop can be 1 if a FpSET_ST0_* was before this. Exchange them.
-      if (StackTop == 1) {
-        BuildMI(*MBB, I, dl, TII->get(X86::XCH_F)).addReg(X86::ST1);
-        ++NumFXCH;
-        StackTop = 0;
-        break;
-      }
-      assert(StackTop == 2 && "Stack should have two element on it to return!");
-      --StackTop;   // "Forget" we have something on the top of stack!
-      break;
-    }
-
     unsigned DestReg = getFPReg(MO0);
     if (MI->killsRegister(X86::FP0+SrcReg)) {
       // If the input operand is killed, we can just change the owner of the