Fix CoerceIntOrPtrToIntOrPtr on big-endian targets.

Type coercion for argument passing is equivalent to storing the source
type and loading the destination type from the same pointer. On
big-endian targets, this means that the high bits of integers are
preserved.

This patch fixes the CoerceIntOrPtrToIntOrPtr() function on big-endian
targets by inserting the required shift instructions to preserve the
high bits instead of the low bits.

This is used by SparcABIInfo when passing small structs in the high bits
of registers.

llvm-svn: 183291

1 files changed, 23 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/CGCall.cpp b/clang/lib/CodeGen/CGCall.cpp
index 3c079cd58bb..a53283eb143 100644
--- a/clang/lib/CodeGen/CGCall.cpp
+++ b/clang/lib/CodeGen/CGCall.cpp
@@ -642,6 +642,10 @@ EnterStructPointerForCoercedAccess(llvm::Value *SrcPtr,
 /// CoerceIntOrPtrToIntOrPtr - Convert a value Val to the specific Ty where both
 /// are either integers or pointers.  This does a truncation of the value if it
 /// is too large or a zero extension if it is too small.
+///
+/// This behaves as if the value were coerced through memory, so on big-endian
+/// targets the high bits are preserved in a truncation, while little-endian
+/// targets preserve the low bits.
 static llvm::Value *CoerceIntOrPtrToIntOrPtr(llvm::Value *Val,
                                              llvm::Type *Ty,
                                              CodeGenFunction &CGF) {
@@ -661,8 +665,25 @@ static llvm::Value *CoerceIntOrPtrToIntOrPtr(llvm::Value *Val,
   if (isa<llvm::PointerType>(DestIntTy))
     DestIntTy = CGF.IntPtrTy;
 
-  if (Val->getType() != DestIntTy)
-    Val = CGF.Builder.CreateIntCast(Val, DestIntTy, false, "coerce.val.ii");
+  if (Val->getType() != DestIntTy) {
+    const llvm::DataLayout &DL = CGF.CGM.getDataLayout();
+    if (DL.isBigEndian()) {
+      // Preserve the high bits on big-endian targets.
+      // That is what memory coercion does.
+      uint64_t SrcSize = DL.getTypeAllocSizeInBits(Val->getType());
+      uint64_t DstSize = DL.getTypeAllocSizeInBits(DestIntTy);
+      if (SrcSize > DstSize) {
+        Val = CGF.Builder.CreateLShr(Val, SrcSize - DstSize, "coerce.highbits");
+        Val = CGF.Builder.CreateTrunc(Val, DestIntTy, "coerce.val.ii");
+      } else {
+        Val = CGF.Builder.CreateZExt(Val, DestIntTy, "coerce.val.ii");
+        Val = CGF.Builder.CreateShl(Val, DstSize - SrcSize, "coerce.highbits");
+      }
+    } else {
+      // Little-endian targets preserve the low bits. No shifts required.
+      Val = CGF.Builder.CreateIntCast(Val, DestIntTy, false, "coerce.val.ii");
+    }
+  }
 
   if (isa<llvm::PointerType>(Ty))
     Val = CGF.Builder.CreateIntToPtr(Val, Ty, "coerce.val.ip");