The x86-64 ABI says that a bool is only guaranteed to be sign-extended to a byte

rather than an int. Thankfully, this only causes LLVM to miss optimizations, not
generate incorrect code.

This just fixes the zext at the return. We still insert an i32 ZextAssert when
reading a function's arguments, but it is followed by a truncate and another i8
ZextAssert so it is not optimized.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127766 91177308-0d34-0410-b5e6-96231b3b80d8

6 files changed, 43 insertions, 10 deletions

diff --git a/docs/LangRef.html b/docs/LangRef.html
index 8938766..ab9f1ca 100644
--- a/docs/LangRef.html
+++ b/docs/LangRef.html
@@ -1017,8 +1017,9 @@ declare signext i8 @returns_signed_char()
 <dl>
   <dt><tt><b>zeroext</b></tt></dt>
   <dd>This indicates to the code generator that the parameter or return value
-      should be zero-extended to a 32-bit value by the caller (for a parameter)
-      or the callee (for a return value).</dd>
+      should be zero-extended to the extent required by the target's ABI (which
+      is usually 32-bits, but is 8-bits for a i1 on x86-64) by the caller (for a
+      parameter) or the callee (for a return value).</dd>
 
   <dt><tt><b>signext</b></tt></dt>
   <dd>This indicates to the code generator that the parameter or return value
diff --git a/include/llvm/Target/TargetLowering.h b/include/llvm/Target/TargetLowering.h
index 618ed54..f257b03 100644
--- a/include/llvm/Target/TargetLowering.h
+++ b/include/llvm/Target/TargetLowering.h
@@ -1287,6 +1287,17 @@ public:
     return false;
   }
 
+  /// getTypeForExtendedInteger - Return the type that should be used to zero or
+  /// sign extend a zeroext/signext integer argument or return value.
+  /// FIXME: Most C calling convention requires the return type to be promoted,
+  /// but this is not true all the time, e.g. i1 on x86-64. It is also not
+  /// necessary for non-C calling conventions. The frontend should handle this
+  /// and include all of the necessary information.
+  virtual MVT
+  getTypeForExtendedInteger(EVT VT, ISD::NodeType ExtendKind) const {
+    return MVT::i32;
+  }
+
   /// LowerOperationWrapper - This callback is invoked by the type legalizer
   /// to legalize nodes with an illegal operand type but legal result types.
   /// It replaces the LowerOperation callback in the type Legalizer.
diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index aa7009a..5548318 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -1128,12 +1128,9 @@ void SelectionDAGBuilder::visitRet(const ReturnInst &I) {
         else if (F->paramHasAttr(0, Attribute::ZExt))
           ExtendKind = ISD::ZERO_EXTEND;
 
-        // FIXME: C calling convention requires the return type to be promoted
-        // to at least 32-bit. But this is not necessary for non-C calling
-        // conventions. The frontend should mark functions whose return values
-        // require promoting with signext or zeroext attributes.
         if (ExtendKind != ISD::ANY_EXTEND && VT.isInteger()) {
-          EVT MinVT = TLI.getRegisterType(*DAG.getContext(), MVT::i32);
+          MVT ReturnMVT = TLI.getTypeForExtendedInteger(VT, ExtendKind);
+          EVT MinVT = TLI.getRegisterType(*DAG.getContext(), ReturnMVT);
           if (VT.bitsLT(MinVT))
             VT = MinVT;
         }
diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 910ed2a..c1aa720 100644
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -1448,6 +1448,15 @@ bool X86TargetLowering::isUsedByReturnOnly(SDNode *N) const {
   return HasRet;
 }
 
+MVT
+X86TargetLowering::getTypeForExtendedInteger(EVT VT,
+                                             ISD::NodeType ExtendKind) const {
+  // TODO: Is this also valid on 32-bit?
+  if (Subtarget->is64Bit() && VT == MVT::i1 && ExtendKind == ISD::ZERO_EXTEND)
+    return MVT::i8;
+  return MVT::i32;
+}
+
 /// LowerCallResult - Lower the result values of a call into the
 /// appropriate copies out of appropriate physical registers.
 ///
diff --git a/lib/Target/X86/X86ISelLowering.h b/lib/Target/X86/X86ISelLowering.h
index 551884b..0857c59 100644
--- a/lib/Target/X86/X86ISelLowering.h
+++ b/lib/Target/X86/X86ISelLowering.h
@@ -843,6 +843,9 @@ namespace llvm {
 
     virtual bool isUsedByReturnOnly(SDNode *N) const;
 
+    virtual MVT
+    getTypeForExtendedInteger(EVT VT, ISD::NodeType ExtendKind) const;
+
     virtual bool
       CanLowerReturn(CallingConv::ID CallConv, bool isVarArg,
                      const SmallVectorImpl<ISD::OutputArg> &Outs,
diff --git a/test/CodeGen/X86/bool-zext.ll b/test/CodeGen/X86/bool-zext.ll
index 67168d4..d2c30c6 100644
--- a/test/CodeGen/X86/bool-zext.ll
+++ b/test/CodeGen/X86/bool-zext.ll
@@ -6,7 +6,7 @@
 define void @bar1(i1 zeroext %v1) nounwind ssp {
 entry:
   %conv = zext i1 %v1 to i32
-  %call = tail call i32 (...)* @foo(i32 %conv) nounwind
+  %call = tail call i32 (...)* @foo1(i32 %conv) nounwind
   ret void
 }
 
@@ -16,8 +16,20 @@ entry:
 define void @bar2(i8 zeroext %v1) nounwind ssp {
 entry:
   %conv = zext i8 %v1 to i32
-  %call = tail call i32 (...)* @foo(i32 %conv) nounwind
+  %call = tail call i32 (...)* @foo1(i32 %conv) nounwind
   ret void
 }
 
-declare i32 @foo(...)
+; CHECK: @bar3
+; CHECK: callq
+; CHECK-NOT: movzbl
+; CHECK-NOT: and
+; CHECK: ret
+define zeroext i1 @bar3() nounwind ssp {
+entry:
+  %call = call i1 @foo2() nounwind
+  ret i1 %call
+}
+
+declare i32 @foo1(...)
+declare zeroext i1 @foo2()