[llvm] [LLVM] BasicTTIImpl allow unknown type during legality checking (PR #89848)

[Billy Zhu via llvm-commits]

https://github.com/zyx-billy created https://github.com/llvm/llvm-project/pull/89848

Make BaseTTIImplBase's `isTypeLegal` check allow unknown types to go through. Current behavior is aborting.

Motivated by a use case in SimplifyCFG, where `isTypeLegal` is called on a struct type and dies, when it could be treated as illegal and skipped. In general it makes sense for unknown types to be allowed through, and by default is considered not legal, but the behavior can of course be overriden.

>From 0e766c461d1d8958dacc1793c07eb95fab698d8c Mon Sep 17 00:00:00 2001
From: Billy Zhu <billyzhu at modular.com>
Date: Mon, 22 Apr 2024 11:05:36 -0700
Subject: [PATCH] allow unknown

---
 llvm/include/llvm/CodeGen/BasicTTIImpl.h      |  2 +-
 .../SimplifyCFG/X86/switch_to_lookup_table.ll | 22 +++++++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/llvm/include/llvm/CodeGen/BasicTTIImpl.h b/llvm/include/llvm/CodeGen/BasicTTIImpl.h
index 06a19c75cf873a..ad7edcf7f9d6a7 100644
--- a/llvm/include/llvm/CodeGen/BasicTTIImpl.h
+++ b/llvm/include/llvm/CodeGen/BasicTTIImpl.h
@@ -426,7 +426,7 @@ class BasicTTIImplBase : public TargetTransformInfoImplCRTPBase<T> {
   bool useAA() const { return getST()->useAA(); }
 
   bool isTypeLegal(Type *Ty) {
-    EVT VT = getTLI()->getValueType(DL, Ty);
+    EVT VT = getTLI()->getValueType(DL, Ty, /*AllowUnknown=*/true);
     return getTLI()->isTypeLegal(VT);
   }
 
diff --git a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
index 3873f0c0ae0bbd..9e3bb2368e7a4d 100644
--- a/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
+++ b/llvm/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
@@ -2068,3 +2068,25 @@ cond.end:                                         ; preds = %entry, %cond.false
   %conv = sext i3 %cond to i8
   ret i8 %conv
 }
+
+; Don't create a table with an unknown type
+define { i8, i8 } @test_unknown_result_type(i8 %n) {
+; CHECK-LABEL: @test_unknown_result_type(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: switch
+entry:
+  switch i8 %n, label %sw.default [
+    i8 0, label %return
+    i8 1, label %return
+    i8 2, label %return
+  ]
+
+sw.default:                                       ; preds = %entry
+  %0 = insertvalue { i8, i8 } undef, i8 0, 0
+  %1 = insertvalue { i8, i8 } %0, i8 1, 1
+  br label %return
+
+return:                                           ; preds = %sw.default, %entry, %entry, %entry
+  %retval.0 = phi { i8, i8 } [ undef, %entry ], [ undef, %entry ], [ undef, %entry ], [ %1, %sw.default ]
+  ret { i8, i8 } %retval.0
+}