[X86] Fix bug in x86_intrcc with arg copy elision

Summary:
Use a custom calling convention handler for interrupts instead of fixing
up the locations in LowerMemArgument. This way, the offsets are correct
when constructed and we don't need to account for them in as many
places.

Depends on D56883

Replaces D56275

Reviewers: craig.topper, phil-opp

Subscribers: hiraditya, llvm-commits

Differential Revision: https://reviews.llvm.org/D56944

llvm-svn: 354837

1 files changed, 40 insertions, 0 deletions

diff --git a/llvm/lib/Target/X86/X86CallingConv.cpp b/llvm/lib/Target/X86/X86CallingConv.cpp
index 7a58e9ae069..9be1147df3c 100644
--- a/llvm/lib/Target/X86/X86CallingConv.cpp
+++ b/llvm/lib/Target/X86/X86CallingConv.cpp
@@ -287,5 +287,45 @@ static bool CC_X86_32_MCUInReg(unsigned &ValNo, MVT &ValVT, MVT &LocVT,
   return true;
 }
 
+/// X86 interrupt handlers can only take one or two stack arguments, but if
+/// there are two arguments, they are in the opposite order from the standard
+/// convention. Therefore, we have to look at the argument count up front before
+/// allocating stack for each argument.
+static bool CC_X86_Intr(unsigned &ValNo, MVT &ValVT, MVT &LocVT,
+                        CCValAssign::LocInfo &LocInfo,
+                        ISD::ArgFlagsTy &ArgFlags, CCState &State) {
+  const MachineFunction &MF = State.getMachineFunction();
+  size_t ArgCount = State.getMachineFunction().getFunction().arg_size();
+  bool Is64Bit = static_cast<const X86Subtarget &>(MF.getSubtarget()).is64Bit();
+  unsigned SlotSize = Is64Bit ? 8 : 4;
+  unsigned Offset;
+  if (ArgCount == 1 && ValNo == 0) {
+    // If we have one argument, the argument is five stack slots big, at fixed
+    // offset zero.
+    Offset = State.AllocateStack(5 * SlotSize, 4);
+  } else if (ArgCount == 2 && ValNo == 0) {
+    // If we have two arguments, the stack slot is *after* the error code
+    // argument. Pretend it doesn't consume stack space, and account for it when
+    // we assign the second argument.
+    Offset = SlotSize;
+  } else if (ArgCount == 2 && ValNo == 1) {
+    // If this is the second of two arguments, it must be the error code. It
+    // appears first on the stack, and is then followed by the five slot
+    // interrupt struct.
+    Offset = 0;
+    (void)State.AllocateStack(6 * SlotSize, 4);
+  } else {
+    report_fatal_error("unsupported x86 interrupt prototype");
+  }
+
+  // FIXME: This should be accounted for in
+  // X86FrameLowering::getFrameIndexReference, not here.
+  if (Is64Bit && ArgCount == 2)
+    Offset += SlotSize;
+
+  State.addLoc(CCValAssign::getMem(ValNo, ValVT, Offset, LocVT, LocInfo));
+  return true;
+}
+
 // Provides entry points of CC_X86 and RetCC_X86.
 #include "X86GenCallingConv.inc"