[MLIR][LLVMIR] Use TargetFolder when creating globals

The LLVM dialect lowers globals using IRBuilder, relying on it
creating constant expressions where possible. As we remove support
for more constant expressions (per https://discourse.llvm.org/t/rfc-remove-most-constant-expressions/63179), this can cause issues for cases where
the constant expression is no longer supported, and the operand
cannot be constant folded without DataLayout being available. In
particular, I ran into this issue with flang and the removal of
mul constant expressions.

Address this by using TargetFolder when creating globals, which
will perform DL-aware constant folding. I think it would make
sense to also do this in general, but I'm starting with globals
where not doing this can result in translation failures.

Ideally, globals with these problematic expressions would never be
generated in the first place, but there has been essentially no
movemenet on fixing this (#96047).

Author: nikic

flang/test/Fir/box.fir

@@ -1,15 +1,15 @@
 // RUN: tco -o - %s | FileCheck %s
 
 // Global box initialization (test must come first because llvm globals are emitted first).
-// CHECK-LABEL: @globalx = internal global { ptr, i64, i32, i8, i8, i8, i8 } { ptr null, i64 ptrtoint (ptr getelementptr (i32, ptr null, i32 1) to i64), i32 20240719, i8 0, i8 9, i8 2, i8 0 }
+// CHECK-LABEL: @globalx = internal global { ptr, i64, i32, i8, i8, i8, i8 } { ptr null, i64 4, i32 20240719, i8 0, i8 9, i8 2, i8 0 }
 fir.global internal @globalx : !fir.box<!fir.heap<i32>> {
   %c0 = arith.constant 0 : index
   %0 = fir.convert %c0 : (index) -> !fir.heap<i32>
   %1 = fir.embox %0 : (!fir.heap<i32>) -> !fir.box<!fir.heap<i32>>
   fir.has_value %1 : !fir.box<!fir.heap<i32>>
 }
 
-// CHECK-LABEL: @globaly = internal global { ptr, i64, i32, i8, i8, i8, i8, [1 x [3 x i64]] } { ptr null, i64 ptrtoint (ptr getelementptr (float, ptr null, i32 1) to i64), i32 20240719, i8 1, i8 27, i8 2, i8 0,{{.*}}[3 x i64] [i64 1, i64 0, i64 ptrtoint (ptr getelementptr (float, ptr null, i32 1) to i64)]
+// CHECK-LABEL: @globaly = internal global { ptr, i64, i32, i8, i8, i8, i8, [1 x [3 x i64]] } { ptr null, i64 4, i32 20240719, i8 1, i8 27, i8 2, i8 0,{{.*}}[3 x i64] [i64 1, i64 0, i64 4]
 fir.global internal @globaly : !fir.box<!fir.heap<!fir.array<?xf32>>> {
   %c0 = arith.constant 0 : index
   %0 = fir.convert %c0 : (index) -> !fir.heap<!fir.array<?xf32>>

flang/test/Fir/rebox-global.fir

@@ -20,4 +20,4 @@ fir.global @pointer_char4_init : !fir.box<!fir.ptr<!fir.char<4,10>>> {
   fir.has_value %2 : !fir.box<!fir.ptr<!fir.char<4,10>>>
 }
 // CHECK-LABEL: @pointer_char4_init
-// CHECK-SAME: { ptr @char4, i64 ptrtoint (ptr getelementptr ([10 x i32], ptr null, i32 1) to i64), i32 20240719, i8 0, i8 44, i8 1, i8 0 }
+// CHECK-SAME: { ptr @char4, i64 40, i32 20240719, i8 0, i8 44, i8 1, i8 0 }

flang/test/Fir/type-descriptor.fir

@@ -13,7 +13,7 @@ fir.global internal @_QFfooEx : !fir.box<!fir.heap<!sometype>> {
   fir.has_value %1 : !fir.box<!fir.heap<!sometype>>
 }
 // CHECK: @_QFfooEx = internal global { ptr, i64, i32, i8, i8, i8, i8, ptr, [1 x i64] }
-// CHECK-SAME: { ptr null, i64 ptrtoint (ptr getelementptr (%_QFfooTsometype, ptr null, i32 1) to i64),
+// CHECK-SAME: { ptr null, i64 80,
 // CHECK-SAME: i32 20240719, i8 0, i8 42, i8 2, i8 1, ptr @_QFfooEXdtXsometype, [1 x i64] zeroinitializer }
 
 !some_pdt_type = !fir.type<_QFfooTsome_pdt_typeK42K43{num:i32,values:!fir.box<!fir.ptr<!fir.array<?x?xf32>>>}>
@@ -25,5 +25,5 @@ fir.global internal @_QFfooEx2 : !fir.box<!fir.heap<!some_pdt_type>> {
   fir.has_value %1 : !fir.box<!fir.heap<!some_pdt_type>>
 }
 // CHECK: @_QFfooEx2 = internal global { ptr, i64, i32, i8, i8, i8, i8, ptr, [1 x i64] }
-// CHECK-SAME: { ptr null, i64 ptrtoint (ptr getelementptr (%_QFfooTsome_pdt_typeK42K43, ptr null, i32 1) to i64),
+// CHECK-SAME: { ptr null, i64 80,
 // CHECK-SAME: i32 20240719, i8 0, i8 42, i8 2, i8 1, ptr @_QFfooEXdtXsome_pdt_typeX42X43, [1 x i64] zeroinitializer }

mlir/lib/Target/LLVMIR/ModuleTranslation.cpp

@@ -38,6 +38,7 @@
 #include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/TypeSwitch.h"
+#include "llvm/Analysis/TargetFolder.h"
 #include "llvm/Frontend/OpenMP/OMPIRBuilder.h"
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/IR/CFG.h"
@@ -1171,7 +1172,9 @@ LogicalResult ModuleTranslation::convertGlobalsAndAliases() {
   // Convert global variable bodies.
   for (auto op : getModuleBody(mlirModule).getOps<LLVM::GlobalOp>()) {
     if (Block *initializer = op.getInitializerBlock()) {
-      llvm::IRBuilder<> builder(llvmModule->getContext());
+      llvm::IRBuilder<llvm::TargetFolder> builder(
+          llvmModule->getContext(),
+          llvm::TargetFolder(llvmModule->getDataLayout()));
 
       [[maybe_unused]] int numConstantsHit = 0;
       [[maybe_unused]] int numConstantsErased = 0;
@@ -1282,7 +1285,9 @@ LogicalResult ModuleTranslation::convertGlobalsAndAliases() {
   // Convert global alias bodies.
   for (auto op : getModuleBody(mlirModule).getOps<LLVM::AliasOp>()) {
     Block &initializer = op.getInitializerBlock();
-    llvm::IRBuilder<> builder(llvmModule->getContext());
+    llvm::IRBuilder<llvm::TargetFolder> builder(
+        llvmModule->getContext(),
+        llvm::TargetFolder(llvmModule->getDataLayout()));
 
     for (mlir::Operation &op : initializer.without_terminator()) {
       if (failed(convertOperation(op, builder)))

mlir/test/Target/LLVMIR/llvmir.mlir

@@ -84,7 +84,7 @@ llvm.mlir.global external @explicit_undef() : i32 {
   llvm.return %0 : i32
 }
 
-// CHECK: @int_gep = internal constant ptr getelementptr (i32, ptr @i32_global, i32 2)
+// CHECK: @int_gep = internal constant ptr getelementptr (i8, ptr @i32_global, i64 8)
 llvm.mlir.global internal constant @int_gep() : !llvm.ptr {
   %addr = llvm.mlir.addressof @i32_global : !llvm.ptr
   %_c0 = llvm.mlir.constant(2: i32) : i32

mlir/test/Target/LLVMIR/omptarget-declare-target-llvm-host.mlir

@@ -133,7 +133,7 @@ module attributes {llvm.target_triple = "x86_64-unknown-linux-gnu", omp.is_targe
     llvm.return %0 : i32
   }
 
-  // CHECK-DAG: @_QMtest_0Ept1 = global { ptr, i64, i32, i8, i8, i8, i8 } { ptr null, i64 ptrtoint (ptr getelementptr (i32, ptr null, i32 1) to i64), i32 20180515, i8 0, i8 9, i8 1, i8 0 }
+  // CHECK-DAG: @_QMtest_0Ept1 = global { ptr, i64, i32, i8, i8, i8, i8 } { ptr null, i64 4, i32 20180515, i8 0, i8 9, i8 1, i8 0 }
   // CHECK-DAG: @_QMtest_0Ept1_decl_tgt_ref_ptr = weak global ptr @_QMtest_0Ept1
   // CHECK-DAG: @.offloading.entry_name{{.*}} = internal unnamed_addr constant [31 x i8] c"_QMtest_0Ept1_decl_tgt_ref_ptr\00"
   // CHECK-DAG: @.offloading.entry._QMtest_0Ept1_decl_tgt_ref_ptr = weak constant %struct.__tgt_offload_entry { i64 0, i16 1, i16 1, i32 1, ptr @_QMtest_0Ept1_decl_tgt_ref_ptr, ptr @.offloading.entry_name{{.*}}, i64 8, i64 0, ptr null }, section "llvm_offload_entries"