[RISCV][TypePromotion] Dont generate truncs if PromotedType is greater than Source Type (#86941)

We currently check if the source and promoted types are not equal before
generating truncate instructions. This does not work for RV64 where the
promoted type is i64 and this lead to a crash due to the generation of
truncate instructions from i32 to i64.

Fixes #86400

Author: svs-quic

llvm/lib/CodeGen/TypePromotion.cpp

@@ -643,7 +643,7 @@ void IRPromoter::ConvertTruncs() {
     ConstantInt *Mask =
         ConstantInt::get(SrcTy, APInt::getMaxValue(NumBits).getZExtValue());
     Value *Masked = Builder.CreateAnd(Trunc->getOperand(0), Mask);
-    if (SrcTy != ExtTy)
+    if (SrcTy->getBitWidth() > ExtTy->getBitWidth())
       Masked = Builder.CreateTrunc(Masked, ExtTy);
 
     if (auto *I = dyn_cast<Instruction>(Masked))

llvm/test/CodeGen/RISCV/rv64-typepromotion.ll

@@ -0,0 +1,27 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt -mtriple=riscv64 -passes=typepromotion -S %s | FileCheck %s
+
+; Test that this does not crash
+define i16 @test(i8 %a, i32 %b) {
+; CHECK-LABEL: define i16 @test(
+; CHECK-SAME: i8 [[A:%.*]], i32 [[B:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = zext i8 [[A]] to i32
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc i32 [[B]] to i16
+; CHECK-NEXT:    [[TMP2:%.*]] = zext i16 [[TMP1]] to i64
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp eq i64 [[TMP2]], 0
+; CHECK-NEXT:    [[TMP4:%.*]] = and i32 [[TMP0]], 255
+; CHECK-NEXT:    [[TMP5:%.*]] = zext i32 [[TMP4]] to i64
+; CHECK-NEXT:    [[TMP6:%.*]] = xor i64 [[TMP5]], [[TMP2]]
+; CHECK-NEXT:    [[TMP7:%.*]] = trunc i64 [[TMP6]] to i16
+; CHECK-NEXT:    ret i16 [[TMP7]]
+;
+entry:
+  %0 = zext i8 %a to i32
+  %1 = trunc i32 %b to i16
+  %2 = icmp eq i16 %1, 0
+  %3 = trunc i32 %0 to i8
+  %4 = zext i8 %3 to i16
+  %5 = xor i16 %4, %1
+  ret i16 %5
+}