[IR] Don't assume all functions are 4 byte aligned

In some cases different alignments for function might be used to save
space e.g. thumb mode with -Oz will try to use 2 byte function
alignment. Similar patch that fixed this in other areas exists here
https://reviews.llvm.org/D46110

This was approved previously https://reviews.llvm.org/D55115 (r348215)
but when committed it caused failures on the sanitizer buildbots when
building llvm with clang (containing this patch). This is now fixed
because I've added a check to see if getting the parent module returns
null if it does then set the alignment to 0.

Differential Revision: https://reviews.llvm.org/D55115

llvm-svn: 348571

llvm/lib/IR/ConstantFold.cpp

@@ -27,6 +27,7 @@
 #include "llvm/IR/GlobalAlias.h"
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm/IR/Module.h"
 #include "llvm/IR/Operator.h"
 #include "llvm/IR/PatternMatch.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -1077,10 +1078,10 @@ Constant *llvm::ConstantFoldBinaryInstruction(unsigned Opcode, Constant *C1,
             isa<GlobalValue>(CE1->getOperand(0))) {
           GlobalValue *GV = cast<GlobalValue>(CE1->getOperand(0));
 
-          // Functions are at least 4-byte aligned.
-          unsigned GVAlign = GV->getAlignment();
-          if (isa<Function>(GV))
-            GVAlign = std::max(GVAlign, 4U);
+          unsigned GVAlign =
+              GV->getParent()
+                  ? GV->getPointerAlignment(GV->getParent()->getDataLayout())
+                  : 0;
 
           if (GVAlign > 1) {
             unsigned DstWidth = CI2->getType()->getBitWidth();

llvm/test/Analysis/ConstantFolding/func-and-folding.ll

@@ -0,0 +1,27 @@
+; RUN: opt < %s -constprop -S -o - | FileCheck %s
+
+; Function Attrs: minsize norecurse nounwind optsize readnone
+define dso_local void @foo1() #0 {
+entry:
+  ret void
+}
+
+; Function Attrs: minsize norecurse nounwind optsize readnone
+define dso_local void @foo2() align 4 {
+entry:
+  ret void
+}
+
+; Function Attrs: minsize nounwind optsize
+define dso_local i32 @main() local_unnamed_addr #1 {
+entry:
+; CHECK: ptrtoint
+  %call = tail call i32 bitcast (i32 (...)* @process to i32 (i32)*)(i32 and (i32 ptrtoint (void ()* @foo1 to i32), i32 2)) #3
+; CHECK-NEXT: ptrtoint
+  %call2 = tail call i32 bitcast (i32 (...)* @process to i32 (i32)*)(i32 and (i32 ptrtoint (void ()* @foo2 to i32), i32 2)) #3
+  ret i32 0
+}
+
+; Function Attrs: minsize optsize
+declare dso_local i32 @process(...) local_unnamed_addr #2
+