[llvm] [CVP] Infer nneg on existing zext (PR #72052)

[Nikita Popov via llvm-commits]

================
@@ -0,0 +1,166 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=correlated-propagation -S | FileCheck %s
+
+; Check that debug locations are preserved. For more info see:
+;   https://llvm.org/docs/SourceLevelDebugging.html#fixing-errors
+; RUN: opt < %s -enable-debugify -passes=correlated-propagation -S 2>&1 | \
+; RUN:   FileCheck %s -check-prefix=DEBUG
+; DEBUG: CheckModuleDebugify: PASS
+
+declare void @use64(i64)
+
+define void @test1(i32 %n) {
+; CHECK-LABEL: @test1(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[FOR_COND:%.*]]
+; CHECK:       for.cond:
+; CHECK-NEXT:    [[A:%.*]] = phi i32 [ [[N:%.*]], [[ENTRY:%.*]] ], [ [[EXT:%.*]], [[FOR_BODY:%.*]] ]
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt i32 [[A]], -1
+; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_BODY]], label [[FOR_END:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    [[EXT_WIDE:%.*]] = zext nneg i32 [[A]] to i64
+; CHECK-NEXT:    call void @use64(i64 [[EXT_WIDE]])
+; CHECK-NEXT:    [[EXT]] = trunc i64 [[EXT_WIDE]] to i32
+; CHECK-NEXT:    br label [[FOR_COND]]
+; CHECK:       for.end:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.body, %entry
+  %a = phi i32 [ %n, %entry ], [ %ext, %for.body ]
+  %cmp = icmp sgt i32 %a, -1
+  br i1 %cmp, label %for.body, label %for.end
+
+for.body:                                         ; preds = %for.cond
+  %ext.wide = zext i32 %a to i64
+  call void @use64(i64 %ext.wide)
+  %ext = trunc i64 %ext.wide to i32
+  br label %for.cond
+
+for.end:                                          ; preds = %for.cond
+  ret void
+}
----------------
nikic wrote:

What is the purpose of these loop test cases?

https://github.com/llvm/llvm-project/pull/72052