InstCombine: teach foldICmpAddConstant about samesign

There are missed optimizations on samesign, due to the predicate being
canonicalized into an equality before we get to our function.

Author: artagnon

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

@@ -3118,7 +3118,7 @@ Instruction *InstCombinerImpl::foldICmpAddConstant(ICmpInst &Cmp,
 
   Value *Op0, *Op1;
   Instruction *Ext0, *Ext1;
-  const CmpInst::Predicate Pred = Cmp.getPredicate();
+  const CmpPredicate Pred = Cmp.getCmpPredicate();
   if (match(Add,
             m_Add(m_CombineAnd(m_Instruction(Ext0), m_ZExtOrSExt(m_Value(Op0))),
                   m_CombineAnd(m_Instruction(Ext1),
@@ -3133,7 +3133,7 @@ Instruction *InstCombinerImpl::foldICmpAddConstant(ICmpInst &Cmp,
         Res += APInt(BW, isa<ZExtInst>(Ext0) ? 1 : -1, /*isSigned=*/true);
       if (Op1Val)
         Res += APInt(BW, isa<ZExtInst>(Ext1) ? 1 : -1, /*isSigned=*/true);
-      return ICmpInst::compare(Res, C, Pred);
+      return ICmpInst::compare(Res, C, Pred.getPreferredSignedPredicate());
     };
 
     Table[0] = ComputeTable(false, false);

llvm/test/Transforms/InstCombine/icmp-add.ll

@@ -1336,8 +1336,7 @@ bb:
 define i1 @test_sext_sext_cvt_2_gt_icmp(i1 %arg, i1 %arg1) {
 ; CHECK-LABEL: @test_sext_sext_cvt_2_gt_icmp(
 ; CHECK-NEXT:  bb:
-; CHECK-NEXT:    [[I4:%.*]] = or i1 [[ARG1:%.*]], [[ARG:%.*]]
-; CHECK-NEXT:    ret i1 [[I4]]
+; CHECK-NEXT:    ret i1 false
 ;
 bb:
   %i = sext i1 %arg to i32
@@ -1476,9 +1475,7 @@ bb:
 define i1 @test_zext_sext_cvt_2_gt_icmp(i1 %arg, i1 %arg1) {
 ; CHECK-LABEL: @test_zext_sext_cvt_2_gt_icmp(
 ; CHECK-NEXT:  bb:
-; CHECK-NEXT:    [[TMP0:%.*]] = xor i1 [[ARG:%.*]], true
-; CHECK-NEXT:    [[I4:%.*]] = and i1 [[ARG1:%.*]], [[TMP0]]
-; CHECK-NEXT:    ret i1 [[I4]]
+; CHECK-NEXT:    ret i1 false
 ;
 bb:
   %i = zext i1 %arg to i32