[CodeGen] Update min-legal-vector width based on function argument and return types

This is a continuation of my patches to inform the X86 backend about what the largest IR types are in the function so that we can restrict the backend type legalizer to prevent 512-bit vectors on SKX when -mprefer-vector-width=256 is specified if no explicit 512 bit vectors were specified by the user.

This patch updates the vector width based on the argument and return types of the current function and from the types of any functions it calls. This is intended to make sure the backend type legalizer doesn't disturb any types that are required for ABI.

Differential Revision: https://reviews.llvm.org/D52441

llvm-svn: 345168

1 files changed, 18 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CodeGenFunction.cpp b/clang/lib/CodeGen/CodeGenFunction.cpp
index 6249ae846dd..41bde79abab 100644
--- a/clang/lib/CodeGen/CodeGenFunction.cpp
+++ b/clang/lib/CodeGen/CodeGenFunction.cpp
@@ -430,7 +430,24 @@ void CodeGenFunction::FinishFunction(SourceLocation EndLoc) {
     NormalCleanupDest = Address::invalid();
   }
 
-  // Add the required-vector-width attribute.
+  // Scan function arguments for vector width.
+  for (llvm::Argument &A : CurFn->args())
+    if (auto *VT = dyn_cast<llvm::VectorType>(A.getType()))
+      LargestVectorWidth = std::max(LargestVectorWidth,
+                                    VT->getPrimitiveSizeInBits());
+
+  // Update vector width based on return type.
+  if (auto *VT = dyn_cast<llvm::VectorType>(CurFn->getReturnType()))
+    LargestVectorWidth = std::max(LargestVectorWidth,
+                                  VT->getPrimitiveSizeInBits());
+
+  // Add the required-vector-width attribute. This contains the max width from:
+  // 1. min-vector-width attribute used in the source program.
+  // 2. Any builtins used that have a vector width specified.
+  // 3. Values passed in and out of inline assembly.
+  // 4. Width of vector arguments and return types for this function.
+  // 5. Width of vector aguments and return types for functions called by this
+  //    function.
   if (LargestVectorWidth != 0)
     CurFn->addFnAttr("min-legal-vector-width",
                      llvm::utostr(LargestVectorWidth));