AMDGPU: Restore using MRI to find highest used regs

If there are no calls, this is a faster path than
searching the entire program for calls.

This was supposed to be left in r309781.
Fixes unused variable warning.

llvm-svn: 309832

1 files changed, 23 insertions, 5 deletions

diff --git a/llvm/lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp b/llvm/lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp
index 1eab96d5e18..36028f7c60e 100644
--- a/llvm/lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp
+++ b/llvm/lib/Target/AMDGPU/AMDGPUAsmPrinter.cpp
@@ -500,13 +500,31 @@ AMDGPUAsmPrinter::SIFunctionResourceInfo AMDGPUAsmPrinter::analyzeResourceUsage(
 
   // If there are no calls, MachineRegisterInfo can tell us the used register
   // count easily.
+  if (!FrameInfo.hasCalls()) {
+    MCPhysReg HighestVGPRReg = AMDGPU::NoRegister;
+    for (MCPhysReg Reg : reverse(AMDGPU::VGPR_32RegClass.getRegisters())) {
+      if (MRI.isPhysRegUsed(Reg)) {
+        HighestVGPRReg = Reg;
+        break;
+      }
+    }
 
-  MCPhysReg HighestVGPRReg = AMDGPU::NoRegister;
-  for (MCPhysReg Reg : reverse(AMDGPU::VGPR_32RegClass.getRegisters())) {
-    if (MRI.isPhysRegUsed(Reg)) {
-      HighestVGPRReg = Reg;
-      break;
+    MCPhysReg HighestSGPRReg = AMDGPU::NoRegister;
+    for (MCPhysReg Reg : reverse(AMDGPU::SGPR_32RegClass.getRegisters())) {
+      if (MRI.isPhysRegUsed(Reg)) {
+        HighestSGPRReg = Reg;
+        break;
+      }
     }
+
+    // We found the maximum register index. They start at 0, so add one to get the
+    // number of registers.
+    Info.NumVGPR = HighestVGPRReg == AMDGPU::NoRegister ? 0 :
+      TRI.getHWRegIndex(HighestVGPRReg) + 1;
+    Info.NumExplicitSGPR = HighestSGPRReg == AMDGPU::NoRegister ? 0 :
+      TRI.getHWRegIndex(HighestSGPRReg) + 1;
+
+    return Info;
   }
 
   int32_t MaxVGPR = -1;