AMDGPU: Respect amdgpu-no-agpr in functions and with calls (#128147)

Remove the MIR scan to detect whether AGPRs are used or not,
and the special case for callable functions. This behavior was
confusing, and not overridable. The amdgpu-no-agpr attribute was
intended to avoid this imprecise heuristic for how many AGPRs to
allocate. It was also too confusing to make this interact with
the pending amdgpu-num-agpr replacement for amdgpu-no-agpr.

Also adds an xfail-ish test where the register allocator asserts
after allocation fails which I ran into.

Future work should reintroduce a more refined MIR scan to estimate
AGPR pressure for how to split AGPRs and VGPRs.

1 files changed, 6 insertions, 48 deletions

diff --git a/llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.cpp b/llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.cpp
index c5efb89..a83fc2d 100644
--- a/llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/SIMachineFunctionInfo.cpp
@@ -64,6 +64,10 @@ SIMachineFunctionInfo::SIMachineFunctionInfo(const Function &F,
   }
 
   MayNeedAGPRs = ST.hasMAIInsts();
+  if (ST.hasGFX90AInsts() &&
+      ST.getMaxNumVGPRs(F) <= AMDGPU::VGPR_32RegClass.getNumRegs() &&
+      !mayUseAGPRs(F))
+    MayNeedAGPRs = false; // We will select all MAI with VGPR operands.
 
   if (AMDGPU::isChainCC(CC)) {
     // Chain functions don't receive an SP from their caller, but are free to
@@ -98,13 +102,8 @@ SIMachineFunctionInfo::SIMachineFunctionInfo(const Function &F,
       ImplicitArgPtr = true;
   } else {
     ImplicitArgPtr = false;
-    MaxKernArgAlign = std::max(ST.getAlignmentForImplicitArgPtr(),
-                               MaxKernArgAlign);
-
-    if (ST.hasGFX90AInsts() &&
-        ST.getMaxNumVGPRs(F) <= AMDGPU::VGPR_32RegClass.getNumRegs() &&
-        !mayUseAGPRs(F))
-      MayNeedAGPRs = false; // We will select all MAI with VGPR operands.
+    MaxKernArgAlign =
+        std::max(ST.getAlignmentForImplicitArgPtr(), MaxKernArgAlign);
   }
 
   if (!AMDGPU::isGraphics(CC) ||
@@ -783,44 +782,3 @@ bool SIMachineFunctionInfo::initializeBaseYamlFields(
 bool SIMachineFunctionInfo::mayUseAGPRs(const Function &F) const {
   return !F.hasFnAttribute("amdgpu-no-agpr");
 }
-
-bool SIMachineFunctionInfo::usesAGPRs(const MachineFunction &MF) const {
-  if (UsesAGPRs)
-    return *UsesAGPRs;
-
-  if (!mayNeedAGPRs()) {
-    UsesAGPRs = false;
-    return false;
-  }
-
-  if (!AMDGPU::isEntryFunctionCC(MF.getFunction().getCallingConv()) ||
-      MF.getFrameInfo().hasCalls()) {
-    UsesAGPRs = true;
-    return true;
-  }
-
-  const MachineRegisterInfo &MRI = MF.getRegInfo();
-
-  for (unsigned I = 0, E = MRI.getNumVirtRegs(); I != E; ++I) {
-    const Register Reg = Register::index2VirtReg(I);
-    const TargetRegisterClass *RC = MRI.getRegClassOrNull(Reg);
-    if (RC && SIRegisterInfo::isAGPRClass(RC)) {
-      UsesAGPRs = true;
-      return true;
-    }
-    if (!RC && !MRI.use_empty(Reg) && MRI.getType(Reg).isValid()) {
-      // Defer caching UsesAGPRs, function might not yet been regbank selected.
-      return true;
-    }
-  }
-
-  for (MCRegister Reg : AMDGPU::AGPR_32RegClass) {
-    if (MRI.isPhysRegUsed(Reg)) {
-      UsesAGPRs = true;
-      return true;
-    }
-  }
-
-  UsesAGPRs = false;
-  return false;
-}