[llvm] r191252 - Selecting the address from a very long chain of GEPs can blow the stack.

[Bill Wendling]

Author: void
Date: Mon Sep 23 19:13:08 2013
New Revision: 191252

URL: http://llvm.org/viewvc/llvm-project?rev=191252&view=rev
Log:
Selecting the address from a very long chain of GEPs can blow the stack.

The recursive nature of the address selection code can cause the stack to
explode if there is a long chain of GEPs. Convert the recursive bit into a
iterative method to avoid this.

<rdar://problem/12445434>

Added:
    llvm/trunk/test/CodeGen/X86/large-gep-chain.ll
Modified:
    llvm/trunk/lib/Target/X86/X86FastISel.cpp

Modified: llvm/trunk/lib/Target/X86/X86FastISel.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86FastISel.cpp?rev=191252&r1=191251&r2=191252&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/X86FastISel.cpp (original)
+++ llvm/trunk/lib/Target/X86/X86FastISel.cpp Mon Sep 23 19:13:08 2013
@@ -347,6 +347,7 @@ bool X86FastISel::X86FastEmitExtend(ISD:
 /// X86SelectAddress - Attempt to fill in an address from the given value.
 ///
 bool X86FastISel::X86SelectAddress(const Value *V, X86AddressMode &AM) {
+redo_gep:
   const User *U = NULL;
   unsigned Opcode = Instruction::UserOp1;
   if (const Instruction *I = dyn_cast<Instruction>(V)) {
@@ -469,16 +470,24 @@ bool X86FastISel::X86SelectAddress(const
         goto unsupported_gep;
       }
     }
+
     // Check for displacement overflow.
     if (!isInt<32>(Disp))
       break;
-    // Ok, the GEP indices were covered by constant-offset and scaled-index
-    // addressing. Update the address state and move on to examining the base.
+
     AM.IndexReg = IndexReg;
     AM.Scale = Scale;
     AM.Disp = (uint32_t)Disp;
-    if (X86SelectAddress(U->getOperand(0), AM))
+
+    if (const GetElementPtrInst *GEP =
+          dyn_cast<GetElementPtrInst>(U->getOperand(0))) {
+      // Ok, the GEP indices were covered by constant-offset and scaled-index
+      // addressing. Update the address state and move on to examining the base.
+      V = GEP;
+      goto redo_gep;
+    } else if (X86SelectAddress(U->getOperand(0), AM)) {
       return true;
+    }
 
     // If we couldn't merge the gep value into this addr mode, revert back to
     // our address and just match the value instead of completely failing.