[ConstantFold] Make areGlobalsPotentiallyEqual less aggressive.

[efriedma]

Summary

In particular, we shouldn't make assumptions about globals which are unnamed_addr: we can fold them together with other globals.

Also while I'm here, use isInterposable() instead of trying to explicitly name all the different kinds of weak linkage.

Fixes https://bugs.llvm.org/show_bug.cgi?id=47090

[fhahn]

LGTM, thanks!

llvm/test/Assembler/ConstantExprNoFold.ll

47

Looks like the precommit checks complain about this. Shouldn't this be c"...." for string constants? Also, it seems like escape sequences are not supported by the bitcode parser and \0 counts as 2 chars.

llvm/lib/IR/ConstantFold.cpp

static FCmpInst::Predicate evaluateFCmpRelation(Constant *V1, Constant *V2) {
   // There are MANY other foldings that we could perform here.  They will
   // probably be added on demand, as they seem needed.
   return FCmpInst::BAD_FCMP_PREDICATE;
 }
 
 static ICmpInst::Predicate areGlobalsPotentiallyEqual(const GlobalValue *GV1,
                                                       const GlobalValue *GV2) {
   auto isGlobalUnsafeForEquality = [](const GlobalValue *GV) {
-    if (GV->hasExternalWeakLinkage() || GV->hasWeakAnyLinkage())
+    if (GV->isInterposable() || GV->hasGlobalUnnamedAddr())
       return true;
     if (const auto *GVar = dyn_cast<GlobalVariable>(GV)) {
       Type *Ty = GVar->getValueType();
       // A global with opaque type might end up being zero sized.
       if (!Ty->isSized())
         return true;
       // A global with an empty type might lie at the address of any other
       // global.

llvm/test/Assembler/ConstantExprNoFold.ll

 @weakany = weak global i32 0
 
 ; Empty globals might end up anywhere, even on top of another global.
 ; CHECK: @empty.cmp = global i1 icmp eq ([0 x i8]* @empty.1, [0 x i8]* @empty.2)
 @empty.1 = external global [0 x i8], align 1
 @empty.2 = external global [0 x i8], align 1
 @empty.cmp = global i1 icmp eq ([0 x i8]* @empty.1, [0 x i8]* @empty.2)
 
+; Two unnamed_addr globals can share an address
+; CHECK: @unnamed.cmp = global i1 icmp eq ([5 x i8]* @unnamed.1, [5 x i8]* @unnamed.2)
+@unnamed.1 = unnamed_addr constant [5 x i8] c"asdf\00"
+@unnamed.2 = unnamed_addr constant [5 x i8] c"asdf\00"
[e-mail] = global i1 icmp eq ([5 x i8]* @unnamed.1, [5 x i8]* @unnamed.2)
+
 @addrspace3 = internal addrspace(3) global i32 undef
 
 ; CHECK: @no.fold.addrspace.icmp.eq.gv.null = global i1 icmp eq (i32 addrspace(3)* @addrspace3, i32 addrspace(3)* null)
 ; CHECK: @no.fold.addrspace.icmp.eq.null.gv = global i1 icmp eq (i32 addrspace(3)* @addrspace3, i32 addrspace(3)* null)
 ; CHECK: @no.fold.addrspace.icmp.ne.gv.null = global i1 icmp ne (i32 addrspace(3)* @addrspace3, i32 addrspace(3)* null)
 ; CHECK: @no.fold.addrspace.icmp.ne.null.gv = global i1 icmp ne (i32 addrspace(3)* @addrspace3, i32 addrspace(3)* null)
 @no.fold.addrspace.icmp.eq.gv.null = global i1 icmp eq (i32 addrspace(3)* @addrspace3, i32 addrspace(3)* null)
 @no.fold.addrspace.icmp.eq.null.gv = global i1 icmp eq (i32 addrspace(3)* null, i32 addrspace(3)* @addrspace3)

llvm/test/Transforms/InstCombine/2010-03-03-ExtElim.ll

; CHECK-LABEL: @PR6486(
   %tmp = load i32**, i32*** @g_177                       ; <i32**> [#uses=1]
   %cmp = icmp ne i32** null, %tmp                 ; <i1> [#uses=1]
   %conv = zext i1 %cmp to i32                     ; <i32> [#uses=1]
   %cmp1 = icmp sle i32 0, %conv                   ; <i1> [#uses=1]
   ret i1 %cmp1
 ; CHECK: ret i1 true
 }
 
-@d = common global i32 0, align 4
-@a = common global [1 x i32] zeroinitializer, align 4
+@d = global i32 0, align 4
+@a = global [1 x i32] zeroinitializer, align 4
 
 define i1 @PR16462_1() nounwind {
 ; CHECK-LABEL: @PR16462_1(
   ret i1 icmp sgt (i32 sext (i16 trunc (i32 select (i1 icmp eq (i32* getelementptr inbounds ([1 x i32], [1 x i32]* @a, i32 0, i32 0), i32* @d), i32 0, i32 1) to i16) to i32), i32 65535)
 ; CHECK: ret i1 false
 }
 
 define i1 @PR16462_2() nounwind {
 ; CHECK-LABEL: @PR16462_2(
   ret i1 icmp sgt (i32 sext (i16 trunc (i32 select (i1 icmp eq (i32* getelementptr inbounds ([1 x i32], [1 x i32]* @a, i32 0, i32 0), i32* @d), i32 0, i32 1) to i16) to i32), i32 42)
 ; CHECK: ret i1 false
 }