[CodeGen] Use pointer-sized integers for ptrtoint sources

Given something like:
void *v = (void *)100;

We need to synthesize a ptrtoint operation from 100.  During constant
emission, we choose i64 as the type for our constant because it
guaranteed not to drop any bits from our CharUnits representation of the
value.  However, this is suboptimal for 32-bit targets: LLVM passes like
GlobalOpt will get confused by these sorts of casts resulting in
pessimization.

Instead, make sure the ptrtoint operand has a pointer-sized integer
type.

llvm-svn: 273020

1 files changed, 7 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CGExprConstant.cpp b/clang/lib/CodeGen/CGExprConstant.cpp
index d64c5876ee2..8ad1a4d29cd 100644
--- a/clang/lib/CodeGen/CGExprConstant.cpp
+++ b/clang/lib/CodeGen/CGExprConstant.cpp
@@ -1314,8 +1314,14 @@ llvm::Constant *CodeGenModule::EmitConstantValue(const APValue &Value,
 
       // Convert to the appropriate type; this could be an lvalue for
       // an integer.
-      if (isa<llvm::PointerType>(DestTy))
+      if (isa<llvm::PointerType>(DestTy)) {
+        // Convert the integer to a pointer-sized integer before converting it
+        // to a pointer.
+        C = llvm::ConstantExpr::getIntegerCast(
+            C, getDataLayout().getIntPtrType(DestTy),
+            /*isSigned=*/false);
         return llvm::ConstantExpr::getIntToPtr(C, DestTy);
+      }
 
       // If the types don't match this should only be a truncate.
       if (C->getType() != DestTy)