[PATCH] D55115: [IR] Don't assume all functions are 4 byte aligned

[Ranjeet Singh via Phabricator via llvm-commits]

rs created this revision.
rs added reviewers: petpav01, olista01.

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


Repository:
  rL LLVM

https://reviews.llvm.org/D55115

Files:
  lib/IR/ConstantFold.cpp
  test/Analysis/ConstantFolding/func-and-folding.ll
  test/Assembler/2004-03-07-FunctionAddressAlignment.ll


Index: test/Assembler/2004-03-07-FunctionAddressAlignment.ll
===================================================================
--- test/Assembler/2004-03-07-FunctionAddressAlignment.ll
+++ test/Assembler/2004-03-07-FunctionAddressAlignment.ll
@@ -3,11 +3,11 @@
 ; All of these should be eliminable
 
 
-define i32 @foo() {
+define i32 @foo() align 4 {
 	ret i32 and (i32 ptrtoint (i32()* @foo to i32), i32 1)
 }
 
-define i32 @foo2() {
+define i32 @foo2() align 4 {
 	ret i32 and (i32 1, i32 ptrtoint (i32()* @foo2 to i32))
 }
 
Index: test/Analysis/ConstantFolding/func-and-folding.ll
===================================================================
--- /dev/null
+++ test/Analysis/ConstantFolding/func-and-folding.ll
@@ -0,0 +1,35 @@
+; 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() #0 {
+entry:
+  ret void
+}
+
+; Function Attrs: minsize norecurse nounwind optsize readnone
+define dso_local void @foo3() 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
+; CHECK-NOT: ptrtoint
+  %call3 = tail call i32 bitcast (i32 (...)* @process to i32 (i32)*)(i32 and (i32 ptrtoint (void ()* @foo3 to i32), i32 2)) #3
+  ret i32 0
+}
+
+; Function Attrs: minsize optsize
+declare dso_local i32 @process(...) local_unnamed_addr #2
+
Index: lib/IR/ConstantFold.cpp
===================================================================
--- lib/IR/ConstantFold.cpp
+++ lib/IR/ConstantFold.cpp
@@ -1077,10 +1077,11 @@
             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);
+
+          // If alignment isn't specified on functions don't assume it.
+          if (isa<Function>(GV) && GVAlign == 0)
+            return nullptr;
 
           if (GVAlign > 1) {
             unsigned DstWidth = CI2->getType()->getBitWidth();


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