[CodeGen] Always expand division larger than i128

[nikic]

Summary

Default MaxDivRemBitWidthSupported to 128, so that divisions larger than 128 bits are always expanded, without requiring additional configuration from the target.

Note that this may still emit calls to __udivti3 on 32-bit targets, which likely don't have an implementation of that builtin. However, I believe this is sufficient to fix https://github.com/llvm/llvm-project/issues/60531, because Zig must already be defining those builtins.

[mgehre-amd]

The change looks correct. Let's wait for somebody else to give their final approval.

[efriedma]

LGTM

llvm/lib/CodeGen/TargetLoweringBase.cpp

TargetLoweringBase::TargetLoweringBase(const TargetMachine &tm) : TM(tm) {
   SchedPreferenceInfo = Sched::ILP;
   GatherAllAliasesMaxDepth = 18;
   IsStrictFPEnabled = DisableStrictNodeMutation;
   MaxBytesForAlignment = 0;
   // TODO: the default will be switched to 0 in the next commit, along
   // with the Target-specific changes necessary.
   MaxAtomicSizeInBitsSupported = 1024;
 
-  MaxDivRemBitWidthSupported = llvm::IntegerType::MAX_INT_BITS;
+  // Assume that even with libcalls, no target supports wider than 128 bit
+  // division.
+  MaxDivRemBitWidthSupported = 128;
 
   MaxLargeFPConvertBitWidthSupported = llvm::IntegerType::MAX_INT_BITS;
 
   MinCmpXchgSizeInBits = 0;
   SupportsUnalignedAtomics = false;
 
   std::fill(std::begin(LibcallRoutineNames), std::end(LibcallRoutineNames), nullptr);
 

llvm/test/CodeGen/Mips/idiv_large.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=mips-- < %s | FileCheck %s
+; RUN: llc -mtriple=mips64-- < %s | FileCheck %s
+
+define i128 @udiv_i128(i128 %x, i128 %y) nounwind {
+; CHECK-LABEL: udiv_i128:
+; CHECK:    jal __udivti3
+  %res = udiv i128 %x, %y
+  ret i128 %res
+}
+
+define i129 @udiv_i129(i129 %x, i129 %y) nounwind {
+; CHECK-LABEL: udiv_i129:
+; CHECK-NOT: jal
+  %res = udiv i129 %x, %y
+  ret i129 %res
+}

llvm/test/CodeGen/PowerPC/idiv_large.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=powerpc-- < %s | FileCheck %s
+; RUN: llc -mtriple=powerpc64-- < %s | FileCheck %s
+
+define i128 @udiv_i128(i128 %x, i128 %y) nounwind {
+; CHECK-LABEL: udiv_i128:
+; CHECK:    bl __udivti3
+  %res = udiv i128 %x, %y
+  ret i128 %res
+}
+
+define i129 @udiv_i129(i129 %x, i129 %y) nounwind {
+; CHECK-LABEL: udiv_i129:
+; CHECK-NOT: bl __
+  %res = udiv i129 %x, %y
+  ret i129 %res
+}

llvm/test/CodeGen/RISCV/idiv_large.ll

+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=riscv32 < %s | FileCheck %s
+; RUN: llc -mtriple=riscv64 < %s | FileCheck %s
+
+define i128 @udiv_i128(i128 %x, i128 %y) nounwind {
+; CHECK-LABEL: udiv_i128:
+; CHECK:    call __udivti3
+  %res = udiv i128 %x, %y
+  ret i128 %res
+}
+
+define i129 @udiv_i129(i129 %x, i129 %y) nounwind {
+; CHECK-LABEL: udiv_i129:
+; CHECK-NOT: call{{.*}}div
+  %res = udiv i129 %x, %y
+  ret i129 %res
+}