commit 3a106e5b2cd9f4073b2961b991ebaeee96786309
author Shilei Tian <i@tianshilei.me> Fri Mar 29 15:59:50 2024 -0400
committer GitHub <noreply@github.com> Fri Mar 29 15:59:50 2024 -0400
tree 7bb3283f08f6d908b596e5cd5c508af460d9c9a7
parent 360f7f5674c4ddef006d233ef7259f8fe07ae81b

[GlobalISel] Fold G_ICMP if possible (#86357)

This patch tries to fold `G_ICMP` if possible.

llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp

diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index c00fe1f..797bbf7 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -3768,9 +3768,11 @@
   }
   case TargetOpcode::G_ATOMIC_CMPXCHG_WITH_SUCCESS: {
     auto [OldValRes, SuccessRes, Addr, CmpVal, NewVal] = MI.getFirst5Regs();
-    MIRBuilder.buildAtomicCmpXchg(OldValRes, Addr, CmpVal, NewVal,
+    Register NewOldValRes = MRI.cloneVirtualRegister(OldValRes);
+    MIRBuilder.buildAtomicCmpXchg(NewOldValRes, Addr, CmpVal, NewVal,
                                   **MI.memoperands_begin());
-    MIRBuilder.buildICmp(CmpInst::ICMP_EQ, SuccessRes, OldValRes, CmpVal);
+    MIRBuilder.buildICmp(CmpInst::ICMP_EQ, SuccessRes, NewOldValRes, CmpVal);
+    MIRBuilder.buildCopy(OldValRes, NewOldValRes);
     MI.eraseFromParent();
     return Legalized;
   }
@@ -3789,8 +3791,12 @@
   case G_UADDO: {
     auto [Res, CarryOut, LHS, RHS] = MI.getFirst4Regs();
 
-    MIRBuilder.buildAdd(Res, LHS, RHS);
-    MIRBuilder.buildICmp(CmpInst::ICMP_ULT, CarryOut, Res, RHS);
+    Register NewRes = MRI.cloneVirtualRegister(Res);
+
+    MIRBuilder.buildAdd(NewRes, LHS, RHS);
+    MIRBuilder.buildICmp(CmpInst::ICMP_ULT, CarryOut, NewRes, RHS);
+
+    MIRBuilder.buildCopy(Res, NewRes);
 
     MI.eraseFromParent();
     return Legalized;
@@ -3800,6 +3806,8 @@
     const LLT CondTy = MRI.getType(CarryOut);
     const LLT Ty = MRI.getType(Res);
 
+    Register NewRes = MRI.cloneVirtualRegister(Res);
+
     // Initial add of the two operands.
     auto TmpRes = MIRBuilder.buildAdd(Ty, LHS, RHS);
 
@@ -3808,15 +3816,18 @@
 
     // Add the sum and the carry.
     auto ZExtCarryIn = MIRBuilder.buildZExt(Ty, CarryIn);
-    MIRBuilder.buildAdd(Res, TmpRes, ZExtCarryIn);
+    MIRBuilder.buildAdd(NewRes, TmpRes, ZExtCarryIn);
 
     // Second check for carry. We can only carry if the initial sum is all 1s
     // and the carry is set, resulting in a new sum of 0.
     auto Zero = MIRBuilder.buildConstant(Ty, 0);
-    auto ResEqZero = MIRBuilder.buildICmp(CmpInst::ICMP_EQ, CondTy, Res, Zero);
+    auto ResEqZero =
+        MIRBuilder.buildICmp(CmpInst::ICMP_EQ, CondTy, NewRes, Zero);
     auto Carry2 = MIRBuilder.buildAnd(CondTy, ResEqZero, CarryIn);
     MIRBuilder.buildOr(CarryOut, Carry, Carry2);
 
+    MIRBuilder.buildCopy(Res, NewRes);
+
     MI.eraseFromParent();
     return Legalized;
   }
@@ -7671,10 +7682,12 @@
   LLT Ty = Dst0Ty;
   LLT BoolTy = Dst1Ty;
 
+  Register NewDst0 = MRI.cloneVirtualRegister(Dst0);
+
   if (IsAdd)
-    MIRBuilder.buildAdd(Dst0, LHS, RHS);
+    MIRBuilder.buildAdd(NewDst0, LHS, RHS);
   else
-    MIRBuilder.buildSub(Dst0, LHS, RHS);
+    MIRBuilder.buildSub(NewDst0, LHS, RHS);
 
   // TODO: If SADDSAT/SSUBSAT is legal, compare results to detect overflow.
 
@@ -7687,12 +7700,15 @@
   // (LHS) if and only if the other operand (RHS) is (non-zero) positive,
   // otherwise there will be overflow.
   auto ResultLowerThanLHS =
-      MIRBuilder.buildICmp(CmpInst::ICMP_SLT, BoolTy, Dst0, LHS);
+      MIRBuilder.buildICmp(CmpInst::ICMP_SLT, BoolTy, NewDst0, LHS);
   auto ConditionRHS = MIRBuilder.buildICmp(
       IsAdd ? CmpInst::ICMP_SLT : CmpInst::ICMP_SGT, BoolTy, RHS, Zero);
 
   MIRBuilder.buildXor(Dst1, ConditionRHS, ResultLowerThanLHS);
+
+  MIRBuilder.buildCopy(Dst0, NewDst0);
   MI.eraseFromParent();
+
   return Legalized;
 }