[TypePromotion] Refine fix sext/zext for promoted constant from D125294.

[craig.topper]

Summary

Reviewing the code again, I believe the sext is needed on the LHS
or RHS for ICmp and only on the RHS for Add/Sub.

Add an opcode check before checking the operand number.

[craig.topper]

Add test

[craig.topper]

I went ahead and pushed this to close out PR55627 which @regehr found. If we need to we can address any comments with a followup patch.

llvm/lib/CodeGen/TypePromotion.cpp

for (auto *V : Visited) {
     for (unsigned i = 0, e = I->getNumOperands(); i < e; ++i) {
       Value *Op = I->getOperand(i);
       if ((Op->getType() == ExtTy) || !isa<IntegerType>(Op->getType()))
         continue;
 
       if (auto *Const = dyn_cast<ConstantInt>(Op)) {
         // For subtract, we don't need to sext the constant. We only put it in
         // SafeWrap because SafeWrap.size() is used elsewhere.
-        Constant *NewConst = (SafeWrap.contains(I) && i == 1 &&
+        // For cmp, we need to sign extend a constant appearing in either
+        // operand. For add, we should only sign extend the RHS.
+        Constant *NewConst = (SafeWrap.contains(I) &&
+                              (I->getOpcode() == Instruction::ICmp || i == 1) &&
                               I->getOpcode() != Instruction::Sub)
                                  ? ConstantExpr::getSExt(Const, ExtTy)
                                  : ConstantExpr::getZExt(Const, ExtTy);
         I->setOperand(i, NewConst);
       } else if (isa<UndefValue>(Op))
         I->setOperand(i, ConstantInt::get(ExtTy, 0));
     }
 

llvm/test/Transforms/TypePromotion/ARM/icmps.ll

 entry:
   %0 = load i8, i8* %a, align 1
   %add.i = add i8 %0, -7
   %cmp = icmp ugt i8 %add.i, -5
   %conv1 = zext i1 %cmp to i32
   ret i32 %conv1
 }
 
+define i32 @icmp_minus_imm_noncanonicalcmp(i8* %a) {
+; CHECK-LABEL: @icmp_minus_imm_noncanonicalcmp(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = load i8, i8* [[A:%.*]], align 1
+; CHECK-NEXT:    [[TMP1:%.*]] = zext i8 [[TMP0]] to i32
+; CHECK-NEXT:    [[ADD_I:%.*]] = add i32 [[TMP1]], -7
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i32 -5, [[ADD_I]]
+; CHECK-NEXT:    [[CONV1:%.*]] = zext i1 [[CMP]] to i32
+; CHECK-NEXT:    ret i32 [[CONV1]]
+;
+entry:
+  %0 = load i8, i8* %a, align 1
+  %add.i = add i8 %0, -7
+  %cmp = icmp ult i8 -5, %add.i
+  %conv1 = zext i1 %cmp to i32
+  ret i32 %conv1
+}
+
 define void @mul_with_neg_imm(i32, i32* %b) {
 ; CHECK-LABEL: @mul_with_neg_imm(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[TMP1:%.*]] = trunc i32 [[TMP0:%.*]] to i8
 ; CHECK-NEXT:    [[TMP2:%.*]] = zext i8 [[TMP1]] to i32
 ; CHECK-NEXT:    [[TMP3:%.*]] = and i32 [[TMP2]], 1
 ; CHECK-NEXT:    [[CONV_I:%.*]] = mul nuw i32 [[TMP3]], 132
 ; CHECK-NEXT:    [[TOBOOL:%.*]] = icmp eq i32 [[CONV_I]], 0