lib/Target/X86/InstSelectSimple.cpp: Start counting arguments with 2,

 because arguments start two stack slots off of EBP. Break out of the
 for loop once the argument is found. Increment the counter at the end
 of the loop instead of the beginning. Use addRegOffset and compute
 the scale * index part at compile time instead of using the fancy
 load instruction. Just because an instruction set has wacky addressing
 modes doesn't mean we ought to use them (at least, if you believe Dave
 Patterson).

lib/Target/X86/X86InstrBuilder.h: Add some comments.

test/Regression/Jello/test-loadstore.ll:  Let main return int 0.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@4999 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 9 insertions, 8 deletions

diff --git a/lib/Target/X86/InstSelectSimple.cpp b/lib/Target/X86/InstSelectSimple.cpp
index 40d757b645..54cf29229d 100644
--- a/lib/Target/X86/InstSelectSimple.cpp
+++ b/lib/Target/X86/InstSelectSimple.cpp
@@ -159,23 +159,24 @@ namespace {
       } else if (Argument *A = dyn_cast<Argument>(V)) {
 	// Find the position of the argument in the argument list.
 	const Function *f = F->getFunction ();
-	int counter = 0, argPosition = -1;
+	// The function's arguments look like this:
+	// [EBP]     -- copy of old EBP
+	// [EBP + 4] -- return address
+	// [EBP + 8] -- first argument (leftmost lexically)
+	// So we want to start with counter = 2.
+	int counter = 2, argPosition = -1;
 	for (Function::const_aiterator ai = f->abegin (), ae = f->aend ();
 	     ai != ae; ++ai) {
-	  ++counter;
 	  if (&(*ai) == A) {
 	    argPosition = counter;
+	    break; // Only need to find it once. ;-)
 	  }
+	  ++counter;
 	}
 	assert (argPosition != -1
 		&& "Argument not found in current function's argument list");
 	// Load it out of the stack frame at EBP + 4*argPosition.
-	// (First, load Reg with argPosition, then load Reg with DWORD
-	// PTR [EBP + 4*Reg].)
-	BuildMI (BB, X86::MOVir32, 1, Reg).addZImm (argPosition);
-	BuildMI (BB, X86::MOVmr32, 4,
-		 Reg).addReg (X86::EBP).addZImm (4).addReg (Reg).addSImm (0);
-        // std::cerr << "ERROR: Arguments not implemented in SimpleInstSel\n";
+	addRegOffset (BuildMI (BB, X86::MOVmr32, 4, Reg), X86::EBP, 4*argPosition);
       }
 
       return Reg;