Subzero: Improve handling of alloca instructions of constant size.

src/IceTargetLoweringX8632.cpp

 //===- subzero/src/IceTargetLoweringX8632.cpp - x86-32 lowering -----------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 469 matching lines @@
         Traits::X86_RET_IP_SIZE_BYTES + PreservedRegsSizeBytes;
     uint32_t StackSize =
         Traits::applyStackAlignment(StackOffset + SpillAreaSizeBytes);
     SpillAreaSizeBytes = StackSize - StackOffset;
   }
 
   // Generate "sub esp, SpillAreaSizeBytes"
   if (SpillAreaSizeBytes)
     _sub(getPhysicalRegister(Traits::RegisterSet::Reg_esp),
          Ctx->getConstantInt32(SpillAreaSizeBytes));
+
+  // Account for alloca instructions with known frame offsets.
+  SpillAreaSizeBytes += FixedAllocaSizeBytes;
+
   Ctx->statsUpdateFrameBytes(SpillAreaSizeBytes);
 
+  // Initialize the stack adjustment so that after all the known-frame-offset
+  // alloca instructions are emitted, the stack adjustment will reach zero.
   resetStackAdjustment();
+  updateStackAdjustment(-FixedAllocaSizeBytes);
 
   // Fill in stack offsets for stack args, and copy args into registers for
   // those that were register-allocated. Args are pushed right to left, so
   // Arg[0] is closest to the stack/frame pointer.
   Variable *FramePtr = getPhysicalRegister(getFrameOrStackReg());
   size_t BasicFrameOffset =
       PreservedRegsSizeBytes + Traits::X86_RET_IP_SIZE_BYTES;
   if (!IsEbpBasedFrame)
     BasicFrameOffset += SpillAreaSizeBytes;
 
   const VarList &Args = Func->getArgs();
   size_t InArgsSizeBytes = 0;
   unsigned NumXmmArgs = 0;
   for (Variable *Arg : Args) {
     // Skip arguments passed in registers.
     if (isVectorType(Arg->getType()) && NumXmmArgs < Traits::X86_MAX_XMM_ARGS) {
       ++NumXmmArgs;
       continue;
     }
-    finishArgumentLowering(Arg, FramePtr, BasicFrameOffset, InArgsSizeBytes);
+    // For esp-based frames, the esp value may not stabilize to its home value
+    // until after all the fixed-size alloca instructions have executed.  In
+    // this case, a stack adjustment is needed when accessing in-args in order
+    // to copy them into registers.
+    size_t StackAdjBytes = IsEbpBasedFrame ? 0 : -FixedAllocaSizeBytes;
+    finishArgumentLowering(Arg, FramePtr, BasicFrameOffset, StackAdjBytes,
+                           InArgsSizeBytes);
   }
 
   // Fill in stack offsets for locals.
   assignVarStackSlots(SortedSpilledVariables, SpillAreaPaddingBytes,
                       SpillAreaSizeBytes, GlobalsAndSubsequentPaddingSize,
                       IsEbpBasedFrame);
   // Assign stack offsets to variables that have been linked to spilled
   // variables.
   for (Variable *Var : VariablesLinkedToSpillSlots) {
     Variable *Linked =
@@ skipping 408 matching lines @@
 // case the high-level table has extra entries.
 #define X(tag, sizeLog2, align, elts, elty, str)                               \
   static_assert(_table1_##tag == _table2_##tag,                                \
                 "Inconsistency between ICETYPEX8632_TABLE and ICETYPE_TABLE");
 ICETYPE_TABLE
 #undef X
 } // end of namespace dummy3
 } // end of anonymous namespace
 
 } // end of namespace Ice