[llvm] [AMDGPU] Remove setcc by using add/sub carryout (PR #155255)

[via llvm-commits]

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@@ -16579,6 +16576,55 @@ SDValue SITargetLowering::performSetCCCombine(SDNode *N,
     }
   }
 
+  // Eliminate setcc by using carryout from add/sub instruction
+
+  // LHS = ADD i64 RHS, Z          LHSlo = UADDO       i32 RHSlo, Zlo
+  // setcc LHS ult RHS     ->      LHSHi = UADDO_CARRY i32 RHShi, Zhi
+  // similarly for subtraction
+
+  // LHS = ADD i64 Y, 1            LHSlo = UADDO       i32 Ylo, 1
+  // setcc LHS eq 0        ->      LHSHi = UADDO_CARRY i32 Yhi, 0
+
+  if (VT == MVT::i64 && ((CC == ISD::SETULT &&
+                          sd_match(LHS, m_Add(m_Specific(RHS), m_Value()))) ||
+                         (CC == ISD::SETUGT &&
+                          sd_match(LHS, m_Sub(m_Specific(RHS), m_Value()))) ||
+                         (CC == ISD::SETEQ && CRHS && CRHS->isZero() &&
+                          sd_match(LHS, m_Add(m_Value(), m_One()))))) {
+    EVT TargetType = MVT::i32;
+    EVT CarryVT = MVT::i1;
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LU-JOHN wrote:

Hardcoded.

https://github.com/llvm/llvm-project/pull/155255