[MLIR][LLVMIR] Use TargetFolder when creating globals (#126745)

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 operation 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 little movement 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"