[ARM][GlobalISel] Remove legacy legalizer rules

[Pierre-vh]

I've been looking at LegacyLegalizerInfo and what its place in GISel is. It seems like it's very close to being deleted so I'm checking if we can remove the last remaining uses of it.

Looks like we can do a drop-in replacement with the new legalizer for ARM.

[llvmbot]

@llvm/pr-subscribers-backend-arm

Author: Pierre van Houtryve (Pierre-vh)

Changes

I've been looking at LegacyLegalizerInfo and what its place in GISel is. It seems like it's very close to being deleted so I'm checking if we can remove the last remaining uses of it.

Looks like we can do a drop-in replacement with the new legalizer for ARM.

---

Full diff: https://github.com/llvm/llvm-project/pull/82619.diff

1 Files Affected:

• (modified) llvm/lib/Target/ARM/ARMLegalizerInfo.cpp (+9-47)

diff --git a/llvm/lib/Target/ARM/ARMLegalizerInfo.cpp b/llvm/lib/Target/ARM/ARMLegalizerInfo.cpp
index c5199aab752726..00a29f8ecb2320 100644
--- a/llvm/lib/Target/ARM/ARMLegalizerInfo.cpp
+++ b/llvm/lib/Target/ARM/ARMLegalizerInfo.cpp
@@ -25,42 +25,6 @@
 using namespace llvm;
 using namespace LegalizeActions;
 
-/// FIXME: The following static functions are SizeChangeStrategy functions
-/// that are meant to temporarily mimic the behaviour of the old legalization
-/// based on doubling/halving non-legal types as closely as possible. This is
-/// not entirly possible as only legalizing the types that are exactly a power
-/// of 2 times the size of the legal types would require specifying all those
-/// sizes explicitly.
-/// In practice, not specifying those isn't a problem, and the below functions
-/// should disappear quickly as we add support for legalizing non-power-of-2
-/// sized types further.
-static void addAndInterleaveWithUnsupported(
-    LegacyLegalizerInfo::SizeAndActionsVec &result,
-    const LegacyLegalizerInfo::SizeAndActionsVec &v) {
-  for (unsigned i = 0; i < v.size(); ++i) {
-    result.push_back(v[i]);
-    if (i + 1 < v[i].first && i + 1 < v.size() &&
-        v[i + 1].first != v[i].first + 1)
-      result.push_back({v[i].first + 1, LegacyLegalizeActions::Unsupported});
-  }
-}
-
-static LegacyLegalizerInfo::SizeAndActionsVec
-widen_8_16(const LegacyLegalizerInfo::SizeAndActionsVec &v) {
-  assert(v.size() >= 1);
-  assert(v[0].first > 17);
-  LegacyLegalizerInfo::SizeAndActionsVec result = {
-      {1, LegacyLegalizeActions::Unsupported},
-      {8, LegacyLegalizeActions::WidenScalar},
-      {9, LegacyLegalizeActions::Unsupported},
-      {16, LegacyLegalizeActions::WidenScalar},
-      {17, LegacyLegalizeActions::Unsupported}};
-  addAndInterleaveWithUnsupported(result, v);
-  auto Largest = result.back().first;
-  result.push_back({Largest + 1, LegacyLegalizeActions::Unsupported});
-  return result;
-}
-
 static bool AEABI(const ARMSubtarget &ST) {
   return ST.isTargetAEABI() || ST.isTargetGNUAEABI() || ST.isTargetMuslAEABI();
 }
@@ -118,15 +82,14 @@ ARMLegalizerInfo::ARMLegalizerInfo(const ARMSubtarget &ST) {
         .libcallFor({s32})
         .clampScalar(0, s32, s32);
 
-  for (unsigned Op : {G_SREM, G_UREM}) {
-    LegacyInfo.setLegalizeScalarToDifferentSizeStrategy(Op, 0, widen_8_16);
-    if (HasHWDivide)
-      LegacyInfo.setAction({Op, s32}, LegacyLegalizeActions::Lower);
-    else if (AEABI(ST))
-      LegacyInfo.setAction({Op, s32}, LegacyLegalizeActions::Custom);
-    else
-      LegacyInfo.setAction({Op, s32}, LegacyLegalizeActions::Libcall);
-  }
+  auto &REMBuilder =
+      getActionDefinitionsBuilder({G_SREM, G_UREM}).minScalar(0, s32);
+  if (HasHWDivide)
+    REMBuilder.lowerFor({s32});
+  else if (AEABI(ST))
+    REMBuilder.customFor({s32});
+  else
+    REMBuilder.libcallFor({s32});
 
   getActionDefinitionsBuilder(G_INTTOPTR)
       .legalFor({{p0, s32}})
@@ -202,8 +165,7 @@ ARMLegalizerInfo::ARMLegalizerInfo(const ARMSubtarget &ST) {
 
     LoadStoreBuilder.maxScalar(0, s32);
 
-    for (auto Ty : {s32, s64})
-      LegacyInfo.setAction({G_FNEG, Ty}, LegacyLegalizeActions::Lower);
+    getActionDefinitionsBuilder(G_FNEG).lowerFor({s32, s64});
 
     getActionDefinitionsBuilder(G_FCONSTANT).customFor({s32, s64});
 

[davemgreen]

I'm not very familiar with the history of LegacyLegalizerInfo, but this looks sensible to me. LGTM, thanks for the patch!