[flang-commits] [clang] [flang] [llvm] [clang-tools-extra] [lldb] [IndVars] Add check of loop invariant for trunc instructions (PR #71072)

[Markos Horro via flang-commits]

================
@@ -0,0 +1,28 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=indvars -S | FileCheck %s
+
+declare void @foo(i16 noundef)
+
+; Function Attrs: mustprogress noreturn uwtable
+define void @bar(i64 noundef %ptr) {
+; CHECK-LABEL: @bar(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = trunc i64 [[PTR:%.*]] to i4
+; CHECK-NEXT:    [[TMP1:%.*]] = zext i4 [[TMP0]] to i16
+; CHECK-NEXT:    br label [[WHILE_BODY:%.*]]
+; CHECK:       while.body:
+; CHECK-NEXT:    tail call void @foo(i16 noundef signext [[TMP1]])
+; CHECK-NEXT:    br label [[WHILE_BODY]]
+;
+entry:
+  br label %while.body
+
+while.body:                                       ; preds = %entry, %while.body
+  %0 = phi i64 [ %ptr, %entry ], [ %add.ptr, %while.body ]
+  %1 = trunc i64 %0 to i16
+  %and = and i16 %1, 15                           ; loop invariant
+  tail call void @foo(i16 noundef signext %and)
----------------
markoshorro wrote:

What I've also observed from the regression is that we have one test failing: `test_11` in `Transforms/IndVarSimplify/X86/eliminate-trunc.ll`.

In concrete, in the function the statement failing is:

```ll
define void @test_11() {
...
bb5:                                              ; preds = %bb5, %bb5
  %_tmp24 = icmp slt i16 %_tmp15, 0
  br i1 %_tmp24, label %bb5, label %bb5
...
}
```

which instead of the expected (as it is currently in the test):

```ll
; CHECK:       bb5:
; CHECK-NEXT:    [[_TMP24:%.*]] = icmp slt i16 poison, 0
; CHECK-NEXT:    br i1 [[_TMP24]], label [[BB5:%.*]], label [[BB5]]
```

It gets simplified to:

```ll
bb5:                                              ; preds = %bb5, %bb5
  br i1 poison, label %bb5, label %bb5
```

I'm assuming this simplification is correct, but I don't understand why this is happening with this change. 


https://github.com/llvm/llvm-project/pull/71072