[InstCombine] Add test for #97053 (NFC)

Author: nikic

llvm/test/Transforms/InstCombine/scalarization.ll

@@ -156,6 +156,35 @@ define i8 @extract_element_binop_splat_variable_index(<4 x i8> %x, i32 %y) {
   ret i8 %r
 }
 
+; We cannot move the extractelement before the sdiv here, because %z may be
+; out of range, making the divisor poison and resulting in immediate UB.
+; FIXME: This is a miscompile.
+define i8 @extract_element_binop_splat_variable_index_may_trap(<4 x i8> %x, <4 x i8> %y, i32 %z) {
+;
+; CHECK-LABEL: @extract_element_binop_splat_variable_index_may_trap(
+; CHECK-NEXT:    [[TMP1:%.*]] = extractelement <4 x i8> [[Y:%.*]], i32 [[Z:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = sdiv i8 42, [[TMP1]]
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %b = sdiv <4 x i8> splat (i8 42), %y
+  %r = extractelement <4 x i8> %b, i32 %z
+  ret i8 %r
+}
+
+; Moving the extractelement first is fine here, because the index is known to
+; be valid, so we can't introduce additional poison.
+define i8 @extract_element_binop_constant_index_may_trap(<4 x i8> %x, <4 x i8> %y, i32 %z) {
+;
+; CHECK-LABEL: @extract_element_binop_constant_index_may_trap(
+; CHECK-NEXT:    [[TMP1:%.*]] = extractelement <4 x i8> [[Y:%.*]], i64 3
+; CHECK-NEXT:    [[R:%.*]] = sdiv i8 42, [[TMP1]]
+; CHECK-NEXT:    ret i8 [[R]]
+;
+  %b = sdiv <4 x i8> splat (i8 42), %y
+  %r = extractelement <4 x i8> %b, i32 3
+  ret i8 %r
+}
+
 define i8 @extract_element_binop_splat_with_undef_variable_index(<4 x i8> %x, i32 %y) {
 ;
 ; CHECK-LABEL: @extract_element_binop_splat_with_undef_variable_index(
@@ -344,8 +373,8 @@ define i1 @extractelt_vector_fcmp_constrhs_dynidx(<2 x float> %arg, i32 %idx) {
 define i1 @extractelt_vector_fcmp_copy_flags(<4 x float> %x) {
 ; CHECK-LABEL: @extractelt_vector_fcmp_copy_flags(
 ; CHECK-NEXT:    [[TMP1:%.*]] = extractelement <4 x float> [[X:%.*]], i64 2
-; CHECK-NEXT:    [[TMP2:%.*]] = fcmp nsz arcp oeq float [[TMP1]], 0.000000e+00
-; CHECK-NEXT:    ret i1 [[TMP2]]
+; CHECK-NEXT:    [[R:%.*]] = fcmp nsz arcp oeq float [[TMP1]], 0.000000e+00
+; CHECK-NEXT:    ret i1 [[R]]
 ;
   %cmp = fcmp nsz arcp oeq <4 x float> %x, zeroinitializer
   %r = extractelement <4 x i1> %cmp, i32 2