[llvm] [ADT] Always use 32-bit size type for SmallVector with 16-bit elements (PR #95536)

[Jay Foad via llvm-commits]

https://github.com/jayfoad created https://github.com/llvm/llvm-project/pull/95536

SmallVector has a special case to allow vector of char to exceed 4 GB in
size on 64-bit hosts. Apply this special case only for 8-bit element
types, instead of all element types < 32 bits.

This makes SmallVector<MCPhysReg> more compact because MCPhysReg is
uint16_t.


>From 01d0beab64ec3b116af082cf3c8425915f4e82b4 Mon Sep 17 00:00:00 2001
From: Jay Foad <jay.foad at amd.com>
Date: Fri, 14 Jun 2024 13:58:27 +0100
Subject: [PATCH] [ADT] Always use 32-bit size type for SmallVector with 16-bit
 elements

SmallVector has a special case to allow vector of char to exceed 4 GB in
size on 64-bit hosts. Apply this special case only for 8-bit element
types, instead of all element types < 32 bits.

This makes SmallVector<MCPhysReg> more compact because MCPhysReg is
uint16_t.
---
 llvm/include/llvm/ADT/SmallVector.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/llvm/include/llvm/ADT/SmallVector.h b/llvm/include/llvm/ADT/SmallVector.h
index 09676d792dfeb..d7e889cc7b1e4 100644
--- a/llvm/include/llvm/ADT/SmallVector.h
+++ b/llvm/include/llvm/ADT/SmallVector.h
@@ -116,8 +116,7 @@ template <class Size_T> class SmallVectorBase {
 
 template <class T>
 using SmallVectorSizeType =
-    std::conditional_t<sizeof(T) < 4 && sizeof(void *) >= 8, uint64_t,
-                       uint32_t>;
+    std::conditional_t<sizeof(T) == 1, uintptr_t, uint32_t>;
 
 /// Figure out the offset of the first element.
 template <class T, typename = void> struct SmallVectorAlignmentAndSize {