fix PR5179 and correctly fix PR5831 to not miscompile.

The X86-64 ABI code didn't handle the case when a struct
would get classified and turn up as "NoClass INTEGER" for
example.  This is perfectly possible when the first slot
is all padding (e.g. due to empty base classes).  In this
situation, the first 8-byte doesn't take a register at all,
only the second 8-byte does.

This fixes this by enhancing the x86-64 abi stuff to allow
and handle this case, reverts the broken fix for PR5831,
and enhances the target independent stuff to be able to 
handle an argument value in registers being accessed at an
offset from the memory value.

This is the last x86-64 calling convention related miscompile
that I'm aware of.

llvm-svn: 109848

1 files changed, 32 insertions, 10 deletions

diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
index be2e9540024..5ea77be07b7 100644
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -1015,11 +1015,6 @@ void X86_64ABIInfo::classify(QualType Ty, uint64_t OffsetBase,
         if (Lo == Memory || Hi == Memory)
           break;
       }
-
-      // If this record has no fields, no bases, no vtable, but isn't empty,
-      // classify as INTEGER.
-      if (CXXRD->isEmpty() && Size)
-        Current = Integer;
     }
 
     // Classify the fields one at a time, merging the results.
@@ -1387,13 +1382,18 @@ classifyReturnType(QualType RetTy) const {
 
   // Check some invariants.
   assert((Hi != Memory || Lo == Memory) && "Invalid memory classification.");
-  assert((Lo != NoClass || Hi == NoClass) && "Invalid null classification.");
   assert((Hi != SSEUp || Lo == SSE) && "Invalid SSEUp classification.");
 
   const llvm::Type *ResType = 0;
   switch (Lo) {
   case NoClass:
-    return ABIArgInfo::getIgnore();
+    if (Hi == NoClass)
+      return ABIArgInfo::getIgnore();
+    // If the low part is just padding, it takes no register, leave ResType
+    // null.
+    assert((Hi == SSE || Hi == Integer || Hi == X87Up) &&
+           "Unknown missing lo part");
+    break;
 
   case SSEUp:
   case X87Up:
@@ -1461,12 +1461,18 @@ classifyReturnType(QualType RetTy) const {
   case Integer: {
     const llvm::Type *HiType =
       GetINTEGERTypeAtOffset(CGT.ConvertTypeRecursive(RetTy), 8, RetTy, 8);
+    if (Lo == NoClass)  // Return HiType at offset 8 in memory.
+      return ABIArgInfo::getDirect(HiType, 8);
+
     ResType = llvm::StructType::get(getVMContext(), ResType, HiType, NULL);
     break;
   }
   case SSE: {
     const llvm::Type *HiType =
       GetSSETypeAtOffset(CGT.ConvertTypeRecursive(RetTy), 8, RetTy, 8);
+    if (Lo == NoClass)  // Return HiType at offset 8 in memory.
+      return ABIArgInfo::getDirect(HiType, 8);
+
     ResType = llvm::StructType::get(getVMContext(), ResType, HiType,NULL);
     break;
   }
@@ -1490,6 +1496,9 @@ classifyReturnType(QualType RetTy) const {
     if (Lo != X87) {
       const llvm::Type *HiType =
         GetSSETypeAtOffset(CGT.ConvertTypeRecursive(RetTy), 8, RetTy, 8);
+      if (Lo == NoClass)  // Return HiType at offset 8 in memory.
+        return ABIArgInfo::getDirect(HiType, 8);
+        
       ResType = llvm::StructType::get(getVMContext(), ResType, HiType, NULL);
     }
     break;
@@ -1506,7 +1515,6 @@ ABIArgInfo X86_64ABIInfo::classifyArgumentType(QualType Ty, unsigned &neededInt,
   // Check some invariants.
   // FIXME: Enforce these by construction.
   assert((Hi != Memory || Lo == Memory) && "Invalid memory classification.");
-  assert((Lo != NoClass || Hi == NoClass) && "Invalid null classification.");
   assert((Hi != SSEUp || Lo == SSE) && "Invalid SSEUp classification.");
 
   neededInt = 0;
@@ -1514,8 +1522,14 @@ ABIArgInfo X86_64ABIInfo::classifyArgumentType(QualType Ty, unsigned &neededInt,
   const llvm::Type *ResType = 0;
   switch (Lo) {
   case NoClass:
-    return ABIArgInfo::getIgnore();
-
+    if (Hi == NoClass)
+      return ABIArgInfo::getIgnore();
+    // If the low part is just padding, it takes no register, leave ResType
+    // null.
+    assert((Hi == SSE || Hi == Integer || Hi == X87Up) &&
+           "Unknown missing lo part");
+    break;
+      
     // AMD64-ABI 3.2.3p3: Rule 1. If the class is MEMORY, pass the argument
     // on the stack.
   case Memory:
@@ -1579,6 +1593,10 @@ ABIArgInfo X86_64ABIInfo::classifyArgumentType(QualType Ty, unsigned &neededInt,
     // Pick an 8-byte type based on the preferred type.
     const llvm::Type *HiType =
       GetINTEGERTypeAtOffset(CGT.ConvertTypeRecursive(Ty), 8, Ty, 8);
+    
+    if (Lo == NoClass)  // Pass HiType at offset 8 in memory.
+      return ABIArgInfo::getDirect(HiType, 8);
+
     ResType = llvm::StructType::get(getVMContext(), ResType, HiType, NULL);
     break;
   }
@@ -1589,6 +1607,10 @@ ABIArgInfo X86_64ABIInfo::classifyArgumentType(QualType Ty, unsigned &neededInt,
   case SSE: {
     const llvm::Type *HiType =
       GetSSETypeAtOffset(CGT.ConvertTypeRecursive(Ty), 8, Ty, 8);
+    
+    if (Lo == NoClass)  // Pass HiType at offset 8 in memory.
+      return ABIArgInfo::getDirect(HiType, 8);
+
     ResType = llvm::StructType::get(getVMContext(), ResType, HiType, NULL);
     ++neededSSE;
     break;